Veterinary Ophthalmology (2014) 17, Supplement 1, 69–75
DOI:10.1111/vop.12139
In vivo confocal microscopy of corneal microscopic foreign bodies in horses Eric C. Ledbetter,*,1 Nita L. Irby* and Deanna M. W. Schaefer† *Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA; and †Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
Address communications to: E. C. Ledbetter Tel.: (607) 253-3060 Fax: (607) 253-3534 e-mail: [email protected] 1
Hospital for Animals, College of Veterinary Medicine, Cornell University, VMC Box 34, Ithaca, NY, 14853-6401, USA
Abstract Objective To describe in vivo corneal confocal microscopy of horses with microscopic corneal foreign bodies and to correlate findings with clinical, cytological, and histopathologic evaluations of clinical cases and foreign body morphologies observed in vitro with the confocal microscope. Animal studied Five horses with microscopic corneal foreign bodies. Procedures Sedated and anesthetized horses were examined with a modified Heidelberg Retina Tomograph II and Rostock Cornea Module. Confocal microscopy images were compared with images from cytologic and histopathologic corneal samples. To establish microscopic morphologic features, confocal microscopy images of burdock pappus bristles and surgical glove powder were obtained by in vitro examination. Results Horses were examined by in vivo confocal microscopy to assist in identifying corneal opacities detected by slit-lamp biomicroscopy, to determine the etiology of clinically idiopathic keratitis, or to localize corneal opacities presumed to be foreign bodies for surgical planning. Corneal foreign bodies presumptively identified by confocal microscopy included burdock pappus bristles, other plant foreign materials, and surgical glove powder. The corneal foreign bodies appeared as moderately or hyper-reflective linear, circular, or oval structures by confocal microscopy and did not resemble any normal anatomic structures. The confocal microscopic identification of the foreign bodies was corroborated by cytologic and histopathologic findings in some horses. The in vivo confocal microscopic appearance of the foreign bodies was consistent with morphologies observed during examination of foreign bodies in vitro. Conclusions In vivo corneal confocal microscopy provides a noninvasive method for the detection, characterization, and localization of microscopic foreign bodies in the equine cornea. Key Words: cornea, foreign body, glove powder, horse, in vivo confocal microscopy, keratitis
INTRODUCTION
Corneal foreign bodies are a common clinical entity in the horse.1–3 The anatomic prominence of the equine globe coupled with frequent exposure to potential environmental hazards contributes to the high incidence of this visionthreatening condition in horses. Macroscopic visual examination and slit-lamp biomicroscopy are adequate to indentify and localize many larger corneal foreign bodies; however, limited magnification and light scattering render these techniques inadequate for some foreign bodies that are microscopic, transparent, or obscured by other corneal © 2014 American College of Veterinary Ophthalmologists
opacities.4 In vivo corneal confocal microscopes permit dramatically higher magnification and resolution imaging of the cornea than what can be achieved with slit-lamp biomicroscopy.5 Optical adjustment of the confocal microscope focal plane also permits imaging at different layers of the cornea and precise depth measurements.6 Morphological features of the normal equine cornea as observed by in vivo confocal microscopy are described, and the use of confocal microscopy to provide a rapid and noninvasive method of diagnosing fungal keratitis in the horse is reported.7,8 In vivo confocal microscopy has a variety of clinical uses in humans with corneal foreign
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bodies, but this application is not described in horses.9–16 The objectives of this study are to describe in vivo confocal microscopy of horses with microscopic corneal foreign bodies and to correlate these findings with clinical, cytological, and histopathologic evaluations of clinical cases. In addition, the appearance of the corneal foreign bodies observed with the confocal microscope in vivo was validated by comparisons to select representative foreign body morphologies observed with the confocal microscope in vitro. MATERIALS AND METHODS
In vivo corneal confocal microscopy of clinical cases Five horses presented to the Cornell University Hospital for Animals (Ithaca, NY, USA) with clinical findings consistent with corneal foreign bodies or with idiopathic keratitis were examined by in vivo corneal confocal microscopy. An etiologic diagnosis of corneal foreign body was confirmed in each horse by various combinations of clinical examination, cytology, and histopathology. Prior to in vivo corneal confocal microscopic examination, each horse received a complete ophthalmic examination, including slit-lamp biomicroscopy (Kowa SL-15; Kowa Co, Tokyo, Japan), indirect ophthalmoscopy (Heine Omegaâ 500; Heine Optotechnik, Herrsching, Germany), Schirmer I tear testing (Intervet Inc., Summit, NJ, USA), applanation tonometry (Tono-Penâ XL; Reichert Inc., Depew, NY, USA), and corneal application of fluorescein stain (Akorn Inc., Buffalo Grove, IL, USA). In vivo corneal confocal microscopic examinations were performed with a modified Heidelberg Retina Tomograph II and Rostock Cornea Module (Heidelberg Engineering, Dossenheim, Germany) using a 639 objective (Carl Zeiss Meditec AG, Jena, Germany) and 400 lm field lens. Examinations were performed with standing sedation in four horses and under general anesthesia in one horse. After the application of topical ophthalmic anesthetic, several drops of contact gel (GenTeal tear gel; Novartis Pharmaceuticals Corp, East Hanover, NJ, USA) were applied to the front of the microscope lens and ocular surface. A sterile, single-use polymethylmethacrylate cap (TomoCap; Heidelberg Engineering) mounted on the microscope lens was positioned perpendicular to, and in slight contact with, the corneal surface. Full-thickness images of corneal lesions were captured with a combination of manual and automated image acquisition modes. Multipoint imaging was performed over the center and around the periphery of each corneal lesion. Confocal microscopy of potential foreign materials in vitro Samples of common burdock (Arctium minus) were collected from pastures in the vicinity of Ithaca, NY. The identification of the plants was verified by evaluation of macroscopic plant features. The dried plants were dissected and the pappus bristles aseptically removed with forceps from the seeds at the base of the florets and placed
into sterile petri dishes. Samples of glove dusting powder were obtained from two brands of sterile surgical gloves (Micro-Touchâ latex surgical gloves; Ansell Healthcare, Dothan, AL, USA; O.R. Classicâ latex surgical gloves; Medline Industries, Mundelein, IL, USA). Sections (2.0 9 2.0 cm) of the gloves were aseptically removed with surgical scissors and placed in sterile petri dishes. The interior surface of the glove sections and burdock bristles was coated with a thin layer of confocal microscopy contact gel and examined with the confocal microscope by manually positioning the uncovered plate against the microscope lens polymethylmethacrylate cap.
Image analysis Following examination, digitized corneal images were analyzed for pathology (Rostock Cornea Module Software Version 1.3.3; Heidelberg Engineering). Measurements were taken with a digital image processing program (IMAGEJ; National Institutes of Health, Bethesda, MD, USA). Only clear images free of motion artifact were used for analyses and measurements. RESULTS
In vivo corneal confocal microscopy of clinical cases Clinical case 1 A 1-year-old Haflinger filly was presented for a 2-week history of uveitis oculus dextra (OD). A large (12 mm) full-thickness corneal foreign body was identified in the superior limbus and penetrating into the peripheral iris. Numerous white and yellow, slightly refractile, microscopic corneal opacities were present in the anterior stroma of the superior cornea surrounding the perforating foreign body (Fig. 1). The horse was anesthetized for foreign body removal and corneal repair. In vivo confocal microscopy was performed under anesthesia to further characterize the microscopic corneal opacities surrounding the larger foreign body. Marked corneal leukocyte, Langerhans cell, and anterior stromal dendritic cell infiltrates were present in the superior cornea in association with extensive corneal vascularization. The large perforating foreign body was highly reflective, with alternating linear bands of relatively dark and relatively light regions, and was too large to fit into a single field of view. Surrounding the large foreign body were approximately 50 hyper-reflective, linear foreign bodies that measured 135–300 lm in length and 7–15 lm in width at the widest point (Fig. 1). Many of the foreign bodies tapered to a fine point. The corneal depth range of the microscopic foreign bodies was recorded (they were restricted to the anterior 300 lm of the corneal stroma), and the distribution of the foreign material within the cornea was established using anatomic landmarks and a surgical marker. The penetrating foreign body was surgically removed and the corneal defect repaired. An anterior lamellar
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(b)
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Figure 1. Corneal plant foreign bodies in a horse: (a) clinical photograph of a large full-thickness corneal foreign body in the superior limbus that is surrounded by numerous white and yellow, slightly refractile, microscopic corneal foreign bodies in the anterior stroma. (b) in vivo corneal confocal photomicrograph displaying a hyper-reflective, tapered, linear foreign body surrounded by leukocytes and corneal vessels, Bar: 50 lm. (c) histopathologic photomicrograph of an anterior lamellar keratectomy specimen stained with H&E, clear refractile angular crystalloid foreign bodies (arrows) surrounded by clear areas and with adjacent neutrophils are present in the anterior stroma.
keratectomy was performed to remove the entire region of cornea containing the microscopic foreign bodies. Histopathologic evaluation of the keratectomy sample revealed neutrophilic inflammation and clear refractile angular crystalloid plant foreign bodies with surrounding clear areas considered consistent with segments of burdock pappus bristles (Fig. 1). Fungal and anaerobic bacterial cultures of corneal specimens were negative, and Enterobacter cloacae was isolated from aerobic culture. The horse’s recovery from surgery was unremarkable and the corneal condition resolved.
Clinical case 2 A 7-year-old Andalusian stallion was presented for a 1-month history of intermittent periocular swelling and ocular discomfort oculus sinistra (OS). Superior eyelid blepharedema was present OS associated with mild palpebral conjunctival hyperemia and chemosis. A small cluster of linear plant foreign bodies, consistent with burdock pappus bristles, was present in the palpebral conjunctiva adjacent to the superior eyelid margin. Multifocal subepithelial linear, yellow, slightly refractile opacities were present in the superonasal cornea (Fig. 2). The cornea was fluorescein negative and otherwise appeared clear during biomicroscopic examination. In vivo confocal microscopy was performed with standing sedation to further characterize the corneal opacities. Approximately 20 hyper-reflective, linear, relatively uniform sized, tapered foreign bodies that measured 150– 200 lm in length and 7–18 lm in width (at the widest point) were identified (Fig. 2). The foreign material was restricted to the anterior 200 lm of the corneal stroma. Rare stromal leukocytes were identified in the region of the foreign bodies, but the cornea was otherwise morphologically normal. The conjunctival foreign bodies were manually removed with forceps. Anterior lamellar keratectomy to remove the
region of the cornea containing foreign material was discussed with the client, but postponed pending assessment of clinical response to conjunctival foreign body removal. The client reported no further episodes of ocular discomfort or eyelid abnormalities. The horse was periodically rechecked during the subsequent 18 months, and the corneal foreign bodies persisted unchanged as observed with slit-lamp biomicroscopy.
Clinical case 3 An 18-year-old Thoroughbred mare was presented for evaluation of a corneal ulcer OS that had been present for 1 month. Blepharospasm and mucopurulent discharge were present OS. There was a 1.0-cm region of subepithelial corneal leukocyte infiltration in the temporal cornea surrounding a punctate brown foreign body consistent with plant material. The cornea was fluorescein negative and otherwise appeared clear during biomicroscopic examination. In vivo confocal microscopy was performed with standing sedation, and a single linear, hyper-reflective foreign body that measured 400–450 lm in length and 40 lm in width was identified immediately posterior to the corneal epithelium. Marked corneal epithelial and stromal leukocyte infiltrates were present in the region of the foreign body. The foreign material was manually removed using a combination of Kimura spatula scraping and Alger brush burr polishing. Aerobic bacterial, anaerobic bacterial, and fungal cultures of corneal specimens were negative. The horse had an unremarkable recovery, and the corneal condition resolved. Clinical case 4 A 20-year-old Percheron mare was presented for evaluation of a 2-week history of idiopathic keratitis OD. Marked blepharospasm was present OD. In the axial cornea were regions of anterior stromal fibrosis and superficial corneal vascularization (Fig. 3). A partially
© 2014 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 17, 69–75
72 ledbetter, irby, and schaefer (a)
(b)
Figure 2. Corneal plant foreign bodies in a horse: (a) clinical photograph of numerous subepithelial linear, yellow, slightly refractile foreign bodies (arrows) in the superonasal cornea. (b) in vivo corneal confocal photomicrograph displaying hyper-reflective, tapered, linear foreign bodies. Bars: 50 lm.
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(b)
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Figure 3. Corneal plant foreign body in a horse: (a) clinical photograph of axial anterior stromal fibrosis, superficial corneal vascularization, stromal leukocyte infiltrates, epithelial mineralization, and a superficial stromal corneal ulcer surrounding a punctate anterior stromal accumulation of yellow foreign material (arrow). (b) in vivo corneal confocal photomicrograph displaying the border of the basal epithelium and a sharply defined region of noncellular, moderately reflective, amorphous foreign material in the anterior stroma. (c) histopathologic photomicrograph of an anterior lamellar keratectomy specimen stained with H&E, an aggregate of partially mineralized foreign material (deeply basophilic granular material) is present and surrounded by hyperplastic corneal epithelium and lymphoplasmacytic inflammation. Bars: 50 lm.
epithelialized, 3.0 mm diameter, superficial stromal corneal ulcer was detected surrounding a punctate anterior stromal accumulation of yellow material. The yellow material was surrounded by a thin ring of fluorescein retention. Adjacent to the corneal ulcer were stromal leukocyte infiltrates and epithelial foci of mineralization. In vivo confocal microscopy was performed with standing sedation. The yellow material in the corneal ulcer appeared as a sharply defined 300-lm-diameter region of noncellular, moderately reflective, amorphous material (Fig. 3). Corneal epithelial cells partially encircled the amorphous material. Surrounding the amorphous material were marked numbers of leukocytes, Langerhans cells, anterior stromal dendritic cells, and highly reflective granular structures considered consistent with corneal mineralization. Standing anterior lamellar keratectomy was performed to remove the entire region of abnormal axial cornea. Histopathologic evaluation of the keratectomy sample revealed mild lymphoplasmacytic keratitis, multifocal stromal fibrosis, epithelial mineralization, and partially miner-
alized plant foreign material (Fig. 3). Aerobic bacterial, anaerobic bacterial, and fungal cultures of corneal specimens were negative. The horse had an unremarkable recovery, and the corneal condition resolved
Clinical case 5 A 13-year-old Oldenburg gelding was presented for evaluation of a 3-week history of corneal ulceration and progressive keratitis OD. The horse had two superficial keratectomies performed by the referring veterinarian during this period for suspected fungal keratitis. A central and temporal superficial stromal ulcer covered approximately 50% of the corneal surface. The exposed corneal surface was irregular with extensive edema, vascularization, and leukocyte infiltrates. An epithelial and subepithelial accumulation of numerous punctate, slightly irregular, spherical, faint white opacities was detected by slit-lamp biomicroscopy in an approximately 2.0 by 1.0-cm region of the inferonasal cornea (Fig. 4). In vivo confocal microscopy was performed with standing sedation. The faint white opacities appeared as innu-
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(b)
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Figure 4. Corneal glove starch foreign bodies in a horse: (a) clinical photograph of numerous epithelial and subepithelial punctate, irregular, spherical, faint white foreign bodies (arrows) adjacent to a region of corneal ulceration, edema, vascularization, and leukocyte infiltrates. (b) in vivo corneal confocal photomicrograph displaying aggregates of 10–35-lm-diameter round and oval structures, with mixed nonhomogenous reflectivity, within the corneal epithelium. (c) cytological photomicrograph of a corneal scraping specimen stained with Wright’s stain, showing neutrophilic inflammation, corneal epithelial cells, and extracellular refractile crystalline structures typical of starch granules. Bars: 50 lm.
merable 10–35-lm-diameter round and oval structures, frequently present in large aggregates of several structures, within all layers of the corneal epithelium and the subepithelial stroma (Fig. 4). The structures were of mixed, nonhomogenous reflectivity and most possessed predominantly moderate or marked reflectivity. Many of the opacities appeared granular or displayed a distinct pattern of concentric rings of varying degrees of reflectivity. Diffuse corneal vascularization and leukocyte infiltrates were also detected. No fungal elements were observed. A corneal scraping was collected for cytologic and microbiologic evaluation. Cytology revealed neutrophilic inflammation and moderate numbers of extracellular crystalline granules typical of surgical glove starch granules (Fig. 4). The granules were often present in aggregates associated with epithelial cells and were 10–25 lm diameter, refractile, and irregularly polygonal. The granules were clear to light blue in color and often had a visible small central Y-shaped fissure. No infectious organisms or other abnormalities were noted. An alpha-hemolytic Streptococcus sp. was recovered on aerobic bacterial culture; anaerobic bacterial and fungal cultures of corneal specimens were negative. The horse was hospitalized for 2 weeks for medical therapy (i.e., topical ciprofloxacin, topical natamycin, topical atropine, and systemic flunixin meglumine) and continued monitoring. During this period, the corneal ulcer rapidly epithelialized, corneal vessels migrated axially, and the inflammatory infiltrate resolved. The region of white corneal opacities gradually decreased in area during the period of hospitalization. After 14 days, the horse was comfortable and the region of faint white opacities had decreased in size to an approximately 1.0 9 1.0 cm region of the inferonasal cornea. The horse was discharged without medications, and the client reported no further episodes of discomfort prior to recheck examination.
During a recheck examination, 8 weeks later, a large region of axial corneal fibrosis was present OD that corresponded to the area of the previous corneal ulcer. The faint white corneal foreign body opacities were no longer visible by slit-lamp biomicroscopy. Repeat in vivo confocal microscopy examination was performed, and no corneal foreign material or leukocytes were detected. The horse received period rechecks for the subsequent 3 years with no further clinical corneal problems.
Confocal microscopy of potential foreign materials in vitro Burdock pappus bristles appeared as highly reflective, linear, banded structures (Fig. 5). Although too large to fit into a single field of view, entire bristles were estimated to be 1500–3000 lm in length. The bristles were 90–110 lm in width at the base and slowly tapered to fine multibarbed points. Barbules emerged from the bristles at regular intervals. The spike-like barbules were 65–150 lm in length 5–20 lm in width at the base and tapered to fine points. Glove dusting powder appeared as 8–25-lm-diameter round and oval structures (Fig. 5). The structures were of non-homogenous reflectivity and varied from moderate to marked reflectivity. Many of the opacities appeared granular or displayed a distinct pattern of concentric rings of varying degrees of reflectivity. The appearance of the glove powder was similar between both glove brands. DISCUSSION
The use of in vivo confocal microscopy to assist in the clinical management of humans with microscopic corneal foreign bodies is described.9–16 Included in the reports of human corneal foreign bodies imaged with confocal microscopy are cotton fibers, pieces of metal, microkeratome plastic particles, pharmaceutical deposits, contact
© 2014 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 17, 69–75
74 ledbetter, irby, and schaefer
Figure 5. Confocal microscopy images of a burdock pappus bristle (a) with prominent barbules (arrow) emerging at regular intervals and surgical glove dusting powder. (b) obtained from in vitro specimens immersed in confocal microscopy contact gel. Bars: 50 lm.
lens fragments, jellyfish tentacle threads, bee stinger fragments, tarantula hairs, and other insect fragments.9–16 In many of the published descriptions, the foreign bodies were not visible with slit-lamp biomicroscopy and were only detected during in vivo confocal microscopic examination of the cornea. The capability to optically section the cornea in vivo in real time, with high magnification and resolution, renders the corneal confocal microscope a valuable clinical tool for the detection, characterization, identification, and localization of corneal foreign bodies. Some of the plant corneal foreign bodies detected in this report were believed to be segments of burdock pappus bristles.17,18 The common burdock (A. minus) is widespread in the Northeast United States, and some of the foreign bodies were morphologically similar to the tapered barbules of burdock pappus bristles when examined with the confocal microscope in vitro. In addition, one horse had concurrent conjunctival foreign bodies that were also consistent with burdock pappus bristles. Burdock pappus bristles are relatively common conjunctival foreign bodies in horses that lead to secondary frictional ulcerative and nonulcerative keratitis.17,18 Whole bristles associated with clinical signs are most frequently embedded in the palpebral or nictitans membrane conjunctiva.17,18 Prior to this series of horses, the authors had noted a clinical association between conjunctival burdock pappus bristles and corneal foreign bodies. This clinical observation, and the results of the present report, suggests that the barbules of burdock pappus bristles should be considered potentially invasive foreign bodies of the cornea as well. Barbules that penetrate the cornea may separate from the pappus bristles at the time of initial ocular exposure or be deposited from bristles that are embedded in the conjunctiva. Presumed surgical glove powder was identified within the corneal epithelium and anterior stroma by both in vivo confocal microscopy and cytology in a horse described in this report. In this horse, it was speculated that the powder was deposited during one of the two keratectomies performed prior to referral. The contribution of the glove powder to the progressive keratitis in the horse is uncertain, but resolution of corneal inflammation following dissipation of the visible intracorneal powder suggests a
potential role. Surgical glove powder lubricants, which included talcum historically and the modern cornstarchbased USP absorbable dusting powder, are widely speculated to induce keratitis in humans following various surgical procedures.19,20 Starch powder contamination of human corneal incisions is reported and implicated in various postoperative corneal complications.21–23 Manufacturers frequently recommend washing of the gloves to remove starch powder prior to surgery; however, glove rinsing is demonstrated to be ineffective in entirely removing powders from surgical gloves and rinsing does not prevent powder implantation in the cornea during ophthalmic surgery.24,25 The frequency of glove powder deposition in surgical wounds of the equine cornea and the potential pathophysiologic ramifications of this powder warrant additional research. As observed in the horses of the present report, the inflammatory response of the cornea to foreign material can vary dramatically between cases. Differences in material composition and antigenicity, biochemical reactions occurring within the tissue, microbial contamination, and the presence of venom or other noxious substances may all contribute to the variable biological reactions observed with corneal foreign bodies.26–29 Due to the unpredictable response of the cornea to foreign materials, removal is advised when clinically feasible. In general, corneal foreign bodies composed of inorganic materials are more likely to be tolerated than organic materials; however, there are rare reports of humans with intracorneal vegetative materials that persisted without recognizable adverse effects for years.30,31 This is similar to one of the horses in the present report, where plant foreign bodies persisted in the corneal stroma without apparent inflammatory reaction or negative sequelae for several months. This suggests that, in horses without clinically detectable inflammatory reaction, corneal foreign body removal may not be an absolute necessity. This manuscript demonstrates the unique ability of in vivo corneal confocal microscopy to provide a rapid, noninvasive method for the detection, characterization, and identification of microscopic foreign bodies in the equine cornea. This imaging technique is useful for
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confocal microscopy of corneal foreign bodies 75
superficial and deep corneal foreign bodies and can be applied to both ulcerative and nonulcerative corneal lesions. Confocal microscopy also permits the detection of infectious agents and leukocytes in the cornea, which can contribute to the selection of a treatment plan.8 The precise anatomic localization and depth measurements supplied by in vivo confocal microscopy can also assist in the selection of therapies and generation of surgical plans. REFERENCES 1. Rebhun WC, Cho JO, Gaarder JE et al. Presumed clostridial and aerobic bacterial infections of the cornea in two horses. Journal of the American Veterinary Medical Association 1999; 214: 1519–1522, 1496. 2. Busse C, Hartley C. Corneal foreign body in a pony. Companion Animal 2010; 15: 4–7. 3. Peiffer RL. Corneoconjunctival foreign body in a horse. Veterinary Medicine, Small Animal Clinician: VM, SAC 1977; 72: 1870–1871. 4. Jalbert I, Stapleton F, Papas E et al. In vivo confocal microscopy of the human cornea. The British Journal of Ophthalmology 2003; 87: 225–236. 5. Patel DV, McGhee CN. Contemporary in vivo confocal microscopy of the living human cornea using white light and laser scanning techniques: a major review. Clinical & Experimental Ophthalmology 2007; 35: 71–88. 6. Bohnke M, Masters BR. Confocal microscopy of the cornea. Progress in Retinal and Eye Research 1999; 18: 553–628. 7. Ledbetter EC, Scarlett JM. In vivo confocal microscopy of the normal equine cornea and limbus. Veterinary Ophthalmology 2009; 12(Suppl 1): 57–64. 8. Ledbetter EC, Irby NL, Kim SG. In vivo confocal microscopy of equine fungal keratitis. Veterinary Ophthalmology 2011; 14: 1–9. 9. Yuen KS, Lai JS, Law RW et al. Confocal microscopy in bee sting corneal injury. Eye (London, England) 2003; 17: 845–847. 10. Kaufman SC, Chew SJ, Capps SC et al. Confocal microscopy of corneal penetration by tarantula hairs. Scanning 1994; 16: 312–315. 11. Awwad ST, Haddad W, Wang MX et al. Corneal intrastromal gatifloxacin crystal deposits after penetrating keratoplasty. Eye & Contact Lens 2004; 30: 169–172. 12. Wong BW, Lai JS, Law RW et al. In vivo confocal microscopy of corneal insect foreign body. Cornea 2003; 22: 56–58. 13. Toshida H, Nakayasu K, Murakami A. In vivo observation of rigid gas-permeable contact lens fragments embedded in cornea. Eye & Contact Lens 2009; 35: 105–107. 14. Sonmez B, Beden U, Yeter V et al. Jellyfish sting injury to the cornea. Ophthalmic Surgery, Lasers & Imaging: The Official Journal of the International Society for Imaging in the Eye 2008; 39: 415–417.
15. Ivarsen A, Thogersen J, Keiding SR et al. Plastic particles at the LASIK interface. Ophthalmology 2004; 111: 18–23. 16. Yuen HK, Lam RF, Kwong YY et al. Retained presumed intraocular cotton fiber after cataract operation: long-term follow-up with in vivo confocal microscopy. Journal of Cataract and Refractive Surgery 2005; 31: 1582–1587. 17. Rebhun WC, Georgi M, Georgi JR. Persistent corneal ulcers in horses caused by embedded burdock pappus bristles. Veterinary Medicine 1991; 86: 930–935. 18. Pickett JP, Crisman MV, Furr MO. Conjunctival foreign body (burdock pappus) induced keratitis in horses: 10 cases. Journal of Equine Veterinary Science 1993; 13: 88–91. 19. Kaufman SC, Maitchouk DY, Chiou AG et al. Interface inflammation after laser in situ keratomileusis. Sands of the Sahara syndrome. Journal of Cataract and Refractive Surgery 1998; 24: 1589–1593. 20. McLeod SD, Tham VM, Phan ST et al. Bilateral diffuse lamellar keratitis following bilateral simultaneous versus sequential laser in situ keratomileusis. The British Journal of Ophthalmology 2003; 87: 1086–1087. 21. Mittelviefhaus H. Corneal infiltrates after keratoplasty caused by tissue inclusions of corn starch glove powder. An intraoperative complication. Der Ophthalmologe : Zeitschrift Der Deutschen Ophthalmologischen Gesellschaft 1993; 90: 720–722. 22. Sellar PW, Sparrow RA. Are ophthalmic surgeons aware that starch powdered surgical gloves are a risk factor in ocular surgery? International Ophthalmology 1998; 22: 247–251. 23. Cox MJ, Woods JA, Newman S et al. Toxic effects of surgical glove powders on the eye. Journal of Long-Term Effects of Medical Implants 1996; 6: 219–226. 24. Stein HA. Powder-free gloves for ophthalmic surgery. Journal of Cataract and Refractive Surgery 1997; 23: 714–717. 25. Hunt TK, Slavin JP, Goodson WH. Starch powder contamination of surgical wounds. Archives of Surgery (Chicago, Ill.: 1960) 1994; 129: 825–827; discussion 828. 26. Portero A, Carreno E, Galarreta D et al. Corneal inflammation from pine processionary caterpillar hairs. Cornea 2013; 32: 161– 164. 27. Macedo Filho ET, Lago A, Duarte K et al. Superficial corneal foreign body: laboratory and epidemiologic aspects. Arquivos Brasileiros de Oftalmologia 2005; 68: 821–823. 28. Cai R, Zhang C, Ding W et al. Corneal melting induced by a presumed copper-containing foreign body. Clinical & Experimental Ophthalmology 2009; 37: 328–330. 29. Smith DG, Roberge RJ. Corneal bee sting with retained stinger. The Journal of Emergency Medicine 2001; 20: 125–128. 30. Covert DJ, Henry CR, Sheth BP. Well-tolerated intracorneal wood foreign body of 40-year duration. Cornea 2009; 28: 597– 598. 31. Dahlan F, Milam DF Jr, Bunt-Milam AH. Long-term corneal retention of a plant foreign body. Cornea 1989; 8: 72–74.
© 2014 American College of Veterinary Ophthalmologists, Veterinary Ophthalmology, 17, 69–75
DOI:10.1111/vop.12139
In vivo confocal microscopy of corneal microscopic foreign bodies in horses Eric C. Ledbetter,*,1 Nita L. Irby* and Deanna M. W. Schaefer† *Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA; and †Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
Address communications to: E. C. Ledbetter Tel.: (607) 253-3060 Fax: (607) 253-3534 e-mail: [email protected] 1
Hospital for Animals, College of Veterinary Medicine, Cornell University, VMC Box 34, Ithaca, NY, 14853-6401, USA
Abstract Objective To describe in vivo corneal confocal microscopy of horses with microscopic corneal foreign bodies and to correlate findings with clinical, cytological, and histopathologic evaluations of clinical cases and foreign body morphologies observed in vitro with the confocal microscope. Animal studied Five horses with microscopic corneal foreign bodies. Procedures Sedated and anesthetized horses were examined with a modified Heidelberg Retina Tomograph II and Rostock Cornea Module. Confocal microscopy images were compared with images from cytologic and histopathologic corneal samples. To establish microscopic morphologic features, confocal microscopy images of burdock pappus bristles and surgical glove powder were obtained by in vitro examination. Results Horses were examined by in vivo confocal microscopy to assist in identifying corneal opacities detected by slit-lamp biomicroscopy, to determine the etiology of clinically idiopathic keratitis, or to localize corneal opacities presumed to be foreign bodies for surgical planning. Corneal foreign bodies presumptively identified by confocal microscopy included burdock pappus bristles, other plant foreign materials, and surgical glove powder. The corneal foreign bodies appeared as moderately or hyper-reflective linear, circular, or oval structures by confocal microscopy and did not resemble any normal anatomic structures. The confocal microscopic identification of the foreign bodies was corroborated by cytologic and histopathologic findings in some horses. The in vivo confocal microscopic appearance of the foreign bodies was consistent with morphologies observed during examination of foreign bodies in vitro. Conclusions In vivo corneal confocal microscopy provides a noninvasive method for the detection, characterization, and localization of microscopic foreign bodies in the equine cornea. Key Words: cornea, foreign body, glove powder, horse, in vivo confocal microscopy, keratitis
INTRODUCTION
Corneal foreign bodies are a common clinical entity in the horse.1–3 The anatomic prominence of the equine globe coupled with frequent exposure to potential environmental hazards contributes to the high incidence of this visionthreatening condition in horses. Macroscopic visual examination and slit-lamp biomicroscopy are adequate to indentify and localize many larger corneal foreign bodies; however, limited magnification and light scattering render these techniques inadequate for some foreign bodies that are microscopic, transparent, or obscured by other corneal © 2014 American College of Veterinary Ophthalmologists
opacities.4 In vivo corneal confocal microscopes permit dramatically higher magnification and resolution imaging of the cornea than what can be achieved with slit-lamp biomicroscopy.5 Optical adjustment of the confocal microscope focal plane also permits imaging at different layers of the cornea and precise depth measurements.6 Morphological features of the normal equine cornea as observed by in vivo confocal microscopy are described, and the use of confocal microscopy to provide a rapid and noninvasive method of diagnosing fungal keratitis in the horse is reported.7,8 In vivo confocal microscopy has a variety of clinical uses in humans with corneal foreign
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bodies, but this application is not described in horses.9–16 The objectives of this study are to describe in vivo confocal microscopy of horses with microscopic corneal foreign bodies and to correlate these findings with clinical, cytological, and histopathologic evaluations of clinical cases. In addition, the appearance of the corneal foreign bodies observed with the confocal microscope in vivo was validated by comparisons to select representative foreign body morphologies observed with the confocal microscope in vitro. MATERIALS AND METHODS
In vivo corneal confocal microscopy of clinical cases Five horses presented to the Cornell University Hospital for Animals (Ithaca, NY, USA) with clinical findings consistent with corneal foreign bodies or with idiopathic keratitis were examined by in vivo corneal confocal microscopy. An etiologic diagnosis of corneal foreign body was confirmed in each horse by various combinations of clinical examination, cytology, and histopathology. Prior to in vivo corneal confocal microscopic examination, each horse received a complete ophthalmic examination, including slit-lamp biomicroscopy (Kowa SL-15; Kowa Co, Tokyo, Japan), indirect ophthalmoscopy (Heine Omegaâ 500; Heine Optotechnik, Herrsching, Germany), Schirmer I tear testing (Intervet Inc., Summit, NJ, USA), applanation tonometry (Tono-Penâ XL; Reichert Inc., Depew, NY, USA), and corneal application of fluorescein stain (Akorn Inc., Buffalo Grove, IL, USA). In vivo corneal confocal microscopic examinations were performed with a modified Heidelberg Retina Tomograph II and Rostock Cornea Module (Heidelberg Engineering, Dossenheim, Germany) using a 639 objective (Carl Zeiss Meditec AG, Jena, Germany) and 400 lm field lens. Examinations were performed with standing sedation in four horses and under general anesthesia in one horse. After the application of topical ophthalmic anesthetic, several drops of contact gel (GenTeal tear gel; Novartis Pharmaceuticals Corp, East Hanover, NJ, USA) were applied to the front of the microscope lens and ocular surface. A sterile, single-use polymethylmethacrylate cap (TomoCap; Heidelberg Engineering) mounted on the microscope lens was positioned perpendicular to, and in slight contact with, the corneal surface. Full-thickness images of corneal lesions were captured with a combination of manual and automated image acquisition modes. Multipoint imaging was performed over the center and around the periphery of each corneal lesion. Confocal microscopy of potential foreign materials in vitro Samples of common burdock (Arctium minus) were collected from pastures in the vicinity of Ithaca, NY. The identification of the plants was verified by evaluation of macroscopic plant features. The dried plants were dissected and the pappus bristles aseptically removed with forceps from the seeds at the base of the florets and placed
into sterile petri dishes. Samples of glove dusting powder were obtained from two brands of sterile surgical gloves (Micro-Touchâ latex surgical gloves; Ansell Healthcare, Dothan, AL, USA; O.R. Classicâ latex surgical gloves; Medline Industries, Mundelein, IL, USA). Sections (2.0 9 2.0 cm) of the gloves were aseptically removed with surgical scissors and placed in sterile petri dishes. The interior surface of the glove sections and burdock bristles was coated with a thin layer of confocal microscopy contact gel and examined with the confocal microscope by manually positioning the uncovered plate against the microscope lens polymethylmethacrylate cap.
Image analysis Following examination, digitized corneal images were analyzed for pathology (Rostock Cornea Module Software Version 1.3.3; Heidelberg Engineering). Measurements were taken with a digital image processing program (IMAGEJ; National Institutes of Health, Bethesda, MD, USA). Only clear images free of motion artifact were used for analyses and measurements. RESULTS
In vivo corneal confocal microscopy of clinical cases Clinical case 1 A 1-year-old Haflinger filly was presented for a 2-week history of uveitis oculus dextra (OD). A large (12 mm) full-thickness corneal foreign body was identified in the superior limbus and penetrating into the peripheral iris. Numerous white and yellow, slightly refractile, microscopic corneal opacities were present in the anterior stroma of the superior cornea surrounding the perforating foreign body (Fig. 1). The horse was anesthetized for foreign body removal and corneal repair. In vivo confocal microscopy was performed under anesthesia to further characterize the microscopic corneal opacities surrounding the larger foreign body. Marked corneal leukocyte, Langerhans cell, and anterior stromal dendritic cell infiltrates were present in the superior cornea in association with extensive corneal vascularization. The large perforating foreign body was highly reflective, with alternating linear bands of relatively dark and relatively light regions, and was too large to fit into a single field of view. Surrounding the large foreign body were approximately 50 hyper-reflective, linear foreign bodies that measured 135–300 lm in length and 7–15 lm in width at the widest point (Fig. 1). Many of the foreign bodies tapered to a fine point. The corneal depth range of the microscopic foreign bodies was recorded (they were restricted to the anterior 300 lm of the corneal stroma), and the distribution of the foreign material within the cornea was established using anatomic landmarks and a surgical marker. The penetrating foreign body was surgically removed and the corneal defect repaired. An anterior lamellar
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(a)
(b)
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Figure 1. Corneal plant foreign bodies in a horse: (a) clinical photograph of a large full-thickness corneal foreign body in the superior limbus that is surrounded by numerous white and yellow, slightly refractile, microscopic corneal foreign bodies in the anterior stroma. (b) in vivo corneal confocal photomicrograph displaying a hyper-reflective, tapered, linear foreign body surrounded by leukocytes and corneal vessels, Bar: 50 lm. (c) histopathologic photomicrograph of an anterior lamellar keratectomy specimen stained with H&E, clear refractile angular crystalloid foreign bodies (arrows) surrounded by clear areas and with adjacent neutrophils are present in the anterior stroma.
keratectomy was performed to remove the entire region of cornea containing the microscopic foreign bodies. Histopathologic evaluation of the keratectomy sample revealed neutrophilic inflammation and clear refractile angular crystalloid plant foreign bodies with surrounding clear areas considered consistent with segments of burdock pappus bristles (Fig. 1). Fungal and anaerobic bacterial cultures of corneal specimens were negative, and Enterobacter cloacae was isolated from aerobic culture. The horse’s recovery from surgery was unremarkable and the corneal condition resolved.
Clinical case 2 A 7-year-old Andalusian stallion was presented for a 1-month history of intermittent periocular swelling and ocular discomfort oculus sinistra (OS). Superior eyelid blepharedema was present OS associated with mild palpebral conjunctival hyperemia and chemosis. A small cluster of linear plant foreign bodies, consistent with burdock pappus bristles, was present in the palpebral conjunctiva adjacent to the superior eyelid margin. Multifocal subepithelial linear, yellow, slightly refractile opacities were present in the superonasal cornea (Fig. 2). The cornea was fluorescein negative and otherwise appeared clear during biomicroscopic examination. In vivo confocal microscopy was performed with standing sedation to further characterize the corneal opacities. Approximately 20 hyper-reflective, linear, relatively uniform sized, tapered foreign bodies that measured 150– 200 lm in length and 7–18 lm in width (at the widest point) were identified (Fig. 2). The foreign material was restricted to the anterior 200 lm of the corneal stroma. Rare stromal leukocytes were identified in the region of the foreign bodies, but the cornea was otherwise morphologically normal. The conjunctival foreign bodies were manually removed with forceps. Anterior lamellar keratectomy to remove the
region of the cornea containing foreign material was discussed with the client, but postponed pending assessment of clinical response to conjunctival foreign body removal. The client reported no further episodes of ocular discomfort or eyelid abnormalities. The horse was periodically rechecked during the subsequent 18 months, and the corneal foreign bodies persisted unchanged as observed with slit-lamp biomicroscopy.
Clinical case 3 An 18-year-old Thoroughbred mare was presented for evaluation of a corneal ulcer OS that had been present for 1 month. Blepharospasm and mucopurulent discharge were present OS. There was a 1.0-cm region of subepithelial corneal leukocyte infiltration in the temporal cornea surrounding a punctate brown foreign body consistent with plant material. The cornea was fluorescein negative and otherwise appeared clear during biomicroscopic examination. In vivo confocal microscopy was performed with standing sedation, and a single linear, hyper-reflective foreign body that measured 400–450 lm in length and 40 lm in width was identified immediately posterior to the corneal epithelium. Marked corneal epithelial and stromal leukocyte infiltrates were present in the region of the foreign body. The foreign material was manually removed using a combination of Kimura spatula scraping and Alger brush burr polishing. Aerobic bacterial, anaerobic bacterial, and fungal cultures of corneal specimens were negative. The horse had an unremarkable recovery, and the corneal condition resolved. Clinical case 4 A 20-year-old Percheron mare was presented for evaluation of a 2-week history of idiopathic keratitis OD. Marked blepharospasm was present OD. In the axial cornea were regions of anterior stromal fibrosis and superficial corneal vascularization (Fig. 3). A partially
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72 ledbetter, irby, and schaefer (a)
(b)
Figure 2. Corneal plant foreign bodies in a horse: (a) clinical photograph of numerous subepithelial linear, yellow, slightly refractile foreign bodies (arrows) in the superonasal cornea. (b) in vivo corneal confocal photomicrograph displaying hyper-reflective, tapered, linear foreign bodies. Bars: 50 lm.
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Figure 3. Corneal plant foreign body in a horse: (a) clinical photograph of axial anterior stromal fibrosis, superficial corneal vascularization, stromal leukocyte infiltrates, epithelial mineralization, and a superficial stromal corneal ulcer surrounding a punctate anterior stromal accumulation of yellow foreign material (arrow). (b) in vivo corneal confocal photomicrograph displaying the border of the basal epithelium and a sharply defined region of noncellular, moderately reflective, amorphous foreign material in the anterior stroma. (c) histopathologic photomicrograph of an anterior lamellar keratectomy specimen stained with H&E, an aggregate of partially mineralized foreign material (deeply basophilic granular material) is present and surrounded by hyperplastic corneal epithelium and lymphoplasmacytic inflammation. Bars: 50 lm.
epithelialized, 3.0 mm diameter, superficial stromal corneal ulcer was detected surrounding a punctate anterior stromal accumulation of yellow material. The yellow material was surrounded by a thin ring of fluorescein retention. Adjacent to the corneal ulcer were stromal leukocyte infiltrates and epithelial foci of mineralization. In vivo confocal microscopy was performed with standing sedation. The yellow material in the corneal ulcer appeared as a sharply defined 300-lm-diameter region of noncellular, moderately reflective, amorphous material (Fig. 3). Corneal epithelial cells partially encircled the amorphous material. Surrounding the amorphous material were marked numbers of leukocytes, Langerhans cells, anterior stromal dendritic cells, and highly reflective granular structures considered consistent with corneal mineralization. Standing anterior lamellar keratectomy was performed to remove the entire region of abnormal axial cornea. Histopathologic evaluation of the keratectomy sample revealed mild lymphoplasmacytic keratitis, multifocal stromal fibrosis, epithelial mineralization, and partially miner-
alized plant foreign material (Fig. 3). Aerobic bacterial, anaerobic bacterial, and fungal cultures of corneal specimens were negative. The horse had an unremarkable recovery, and the corneal condition resolved
Clinical case 5 A 13-year-old Oldenburg gelding was presented for evaluation of a 3-week history of corneal ulceration and progressive keratitis OD. The horse had two superficial keratectomies performed by the referring veterinarian during this period for suspected fungal keratitis. A central and temporal superficial stromal ulcer covered approximately 50% of the corneal surface. The exposed corneal surface was irregular with extensive edema, vascularization, and leukocyte infiltrates. An epithelial and subepithelial accumulation of numerous punctate, slightly irregular, spherical, faint white opacities was detected by slit-lamp biomicroscopy in an approximately 2.0 by 1.0-cm region of the inferonasal cornea (Fig. 4). In vivo confocal microscopy was performed with standing sedation. The faint white opacities appeared as innu-
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Figure 4. Corneal glove starch foreign bodies in a horse: (a) clinical photograph of numerous epithelial and subepithelial punctate, irregular, spherical, faint white foreign bodies (arrows) adjacent to a region of corneal ulceration, edema, vascularization, and leukocyte infiltrates. (b) in vivo corneal confocal photomicrograph displaying aggregates of 10–35-lm-diameter round and oval structures, with mixed nonhomogenous reflectivity, within the corneal epithelium. (c) cytological photomicrograph of a corneal scraping specimen stained with Wright’s stain, showing neutrophilic inflammation, corneal epithelial cells, and extracellular refractile crystalline structures typical of starch granules. Bars: 50 lm.
merable 10–35-lm-diameter round and oval structures, frequently present in large aggregates of several structures, within all layers of the corneal epithelium and the subepithelial stroma (Fig. 4). The structures were of mixed, nonhomogenous reflectivity and most possessed predominantly moderate or marked reflectivity. Many of the opacities appeared granular or displayed a distinct pattern of concentric rings of varying degrees of reflectivity. Diffuse corneal vascularization and leukocyte infiltrates were also detected. No fungal elements were observed. A corneal scraping was collected for cytologic and microbiologic evaluation. Cytology revealed neutrophilic inflammation and moderate numbers of extracellular crystalline granules typical of surgical glove starch granules (Fig. 4). The granules were often present in aggregates associated with epithelial cells and were 10–25 lm diameter, refractile, and irregularly polygonal. The granules were clear to light blue in color and often had a visible small central Y-shaped fissure. No infectious organisms or other abnormalities were noted. An alpha-hemolytic Streptococcus sp. was recovered on aerobic bacterial culture; anaerobic bacterial and fungal cultures of corneal specimens were negative. The horse was hospitalized for 2 weeks for medical therapy (i.e., topical ciprofloxacin, topical natamycin, topical atropine, and systemic flunixin meglumine) and continued monitoring. During this period, the corneal ulcer rapidly epithelialized, corneal vessels migrated axially, and the inflammatory infiltrate resolved. The region of white corneal opacities gradually decreased in area during the period of hospitalization. After 14 days, the horse was comfortable and the region of faint white opacities had decreased in size to an approximately 1.0 9 1.0 cm region of the inferonasal cornea. The horse was discharged without medications, and the client reported no further episodes of discomfort prior to recheck examination.
During a recheck examination, 8 weeks later, a large region of axial corneal fibrosis was present OD that corresponded to the area of the previous corneal ulcer. The faint white corneal foreign body opacities were no longer visible by slit-lamp biomicroscopy. Repeat in vivo confocal microscopy examination was performed, and no corneal foreign material or leukocytes were detected. The horse received period rechecks for the subsequent 3 years with no further clinical corneal problems.
Confocal microscopy of potential foreign materials in vitro Burdock pappus bristles appeared as highly reflective, linear, banded structures (Fig. 5). Although too large to fit into a single field of view, entire bristles were estimated to be 1500–3000 lm in length. The bristles were 90–110 lm in width at the base and slowly tapered to fine multibarbed points. Barbules emerged from the bristles at regular intervals. The spike-like barbules were 65–150 lm in length 5–20 lm in width at the base and tapered to fine points. Glove dusting powder appeared as 8–25-lm-diameter round and oval structures (Fig. 5). The structures were of non-homogenous reflectivity and varied from moderate to marked reflectivity. Many of the opacities appeared granular or displayed a distinct pattern of concentric rings of varying degrees of reflectivity. The appearance of the glove powder was similar between both glove brands. DISCUSSION
The use of in vivo confocal microscopy to assist in the clinical management of humans with microscopic corneal foreign bodies is described.9–16 Included in the reports of human corneal foreign bodies imaged with confocal microscopy are cotton fibers, pieces of metal, microkeratome plastic particles, pharmaceutical deposits, contact
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Figure 5. Confocal microscopy images of a burdock pappus bristle (a) with prominent barbules (arrow) emerging at regular intervals and surgical glove dusting powder. (b) obtained from in vitro specimens immersed in confocal microscopy contact gel. Bars: 50 lm.
lens fragments, jellyfish tentacle threads, bee stinger fragments, tarantula hairs, and other insect fragments.9–16 In many of the published descriptions, the foreign bodies were not visible with slit-lamp biomicroscopy and were only detected during in vivo confocal microscopic examination of the cornea. The capability to optically section the cornea in vivo in real time, with high magnification and resolution, renders the corneal confocal microscope a valuable clinical tool for the detection, characterization, identification, and localization of corneal foreign bodies. Some of the plant corneal foreign bodies detected in this report were believed to be segments of burdock pappus bristles.17,18 The common burdock (A. minus) is widespread in the Northeast United States, and some of the foreign bodies were morphologically similar to the tapered barbules of burdock pappus bristles when examined with the confocal microscope in vitro. In addition, one horse had concurrent conjunctival foreign bodies that were also consistent with burdock pappus bristles. Burdock pappus bristles are relatively common conjunctival foreign bodies in horses that lead to secondary frictional ulcerative and nonulcerative keratitis.17,18 Whole bristles associated with clinical signs are most frequently embedded in the palpebral or nictitans membrane conjunctiva.17,18 Prior to this series of horses, the authors had noted a clinical association between conjunctival burdock pappus bristles and corneal foreign bodies. This clinical observation, and the results of the present report, suggests that the barbules of burdock pappus bristles should be considered potentially invasive foreign bodies of the cornea as well. Barbules that penetrate the cornea may separate from the pappus bristles at the time of initial ocular exposure or be deposited from bristles that are embedded in the conjunctiva. Presumed surgical glove powder was identified within the corneal epithelium and anterior stroma by both in vivo confocal microscopy and cytology in a horse described in this report. In this horse, it was speculated that the powder was deposited during one of the two keratectomies performed prior to referral. The contribution of the glove powder to the progressive keratitis in the horse is uncertain, but resolution of corneal inflammation following dissipation of the visible intracorneal powder suggests a
potential role. Surgical glove powder lubricants, which included talcum historically and the modern cornstarchbased USP absorbable dusting powder, are widely speculated to induce keratitis in humans following various surgical procedures.19,20 Starch powder contamination of human corneal incisions is reported and implicated in various postoperative corneal complications.21–23 Manufacturers frequently recommend washing of the gloves to remove starch powder prior to surgery; however, glove rinsing is demonstrated to be ineffective in entirely removing powders from surgical gloves and rinsing does not prevent powder implantation in the cornea during ophthalmic surgery.24,25 The frequency of glove powder deposition in surgical wounds of the equine cornea and the potential pathophysiologic ramifications of this powder warrant additional research. As observed in the horses of the present report, the inflammatory response of the cornea to foreign material can vary dramatically between cases. Differences in material composition and antigenicity, biochemical reactions occurring within the tissue, microbial contamination, and the presence of venom or other noxious substances may all contribute to the variable biological reactions observed with corneal foreign bodies.26–29 Due to the unpredictable response of the cornea to foreign materials, removal is advised when clinically feasible. In general, corneal foreign bodies composed of inorganic materials are more likely to be tolerated than organic materials; however, there are rare reports of humans with intracorneal vegetative materials that persisted without recognizable adverse effects for years.30,31 This is similar to one of the horses in the present report, where plant foreign bodies persisted in the corneal stroma without apparent inflammatory reaction or negative sequelae for several months. This suggests that, in horses without clinically detectable inflammatory reaction, corneal foreign body removal may not be an absolute necessity. This manuscript demonstrates the unique ability of in vivo corneal confocal microscopy to provide a rapid, noninvasive method for the detection, characterization, and identification of microscopic foreign bodies in the equine cornea. This imaging technique is useful for
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superficial and deep corneal foreign bodies and can be applied to both ulcerative and nonulcerative corneal lesions. Confocal microscopy also permits the detection of infectious agents and leukocytes in the cornea, which can contribute to the selection of a treatment plan.8 The precise anatomic localization and depth measurements supplied by in vivo confocal microscopy can also assist in the selection of therapies and generation of surgical plans. REFERENCES 1. Rebhun WC, Cho JO, Gaarder JE et al. Presumed clostridial and aerobic bacterial infections of the cornea in two horses. Journal of the American Veterinary Medical Association 1999; 214: 1519–1522, 1496. 2. Busse C, Hartley C. Corneal foreign body in a pony. Companion Animal 2010; 15: 4–7. 3. Peiffer RL. Corneoconjunctival foreign body in a horse. Veterinary Medicine, Small Animal Clinician: VM, SAC 1977; 72: 1870–1871. 4. Jalbert I, Stapleton F, Papas E et al. In vivo confocal microscopy of the human cornea. The British Journal of Ophthalmology 2003; 87: 225–236. 5. Patel DV, McGhee CN. Contemporary in vivo confocal microscopy of the living human cornea using white light and laser scanning techniques: a major review. Clinical & Experimental Ophthalmology 2007; 35: 71–88. 6. Bohnke M, Masters BR. Confocal microscopy of the cornea. Progress in Retinal and Eye Research 1999; 18: 553–628. 7. Ledbetter EC, Scarlett JM. In vivo confocal microscopy of the normal equine cornea and limbus. Veterinary Ophthalmology 2009; 12(Suppl 1): 57–64. 8. Ledbetter EC, Irby NL, Kim SG. In vivo confocal microscopy of equine fungal keratitis. Veterinary Ophthalmology 2011; 14: 1–9. 9. Yuen KS, Lai JS, Law RW et al. Confocal microscopy in bee sting corneal injury. Eye (London, England) 2003; 17: 845–847. 10. Kaufman SC, Chew SJ, Capps SC et al. Confocal microscopy of corneal penetration by tarantula hairs. Scanning 1994; 16: 312–315. 11. Awwad ST, Haddad W, Wang MX et al. Corneal intrastromal gatifloxacin crystal deposits after penetrating keratoplasty. Eye & Contact Lens 2004; 30: 169–172. 12. Wong BW, Lai JS, Law RW et al. In vivo confocal microscopy of corneal insect foreign body. Cornea 2003; 22: 56–58. 13. Toshida H, Nakayasu K, Murakami A. In vivo observation of rigid gas-permeable contact lens fragments embedded in cornea. Eye & Contact Lens 2009; 35: 105–107. 14. Sonmez B, Beden U, Yeter V et al. Jellyfish sting injury to the cornea. Ophthalmic Surgery, Lasers & Imaging: The Official Journal of the International Society for Imaging in the Eye 2008; 39: 415–417.
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