Results of Lamellar Crescentic Resection for Pellucid Marginal Corneal Degeneration James A. Cameron, M . D .
Five eyes in four patients with pellucid marginal corneal degeneration were treated by lamellar crescentic resection of the thinned area inferiorly. Normal-thickness stroma was then reapposed to normal-thickness stroma with multiple interrupted 10-0 polypropylene sutures. If excessive central corneal steepen ing along a vertical meridian was present three months after surgery, selected sutures were cut and removed depending on the slitlamp appearance, keratometry reading, and photokeratograph pattern. Improvement of visual acuity to 20/40 or better was obtained in four of the five eyes with a follow-up of 27 to 40 months (mean, 31.8 months). Early loos ening of sutures resulted in a recurrence of corneal thinning and astigmatism in one eye. Fannus developed inferiorly in all five eyes. 1 ELLUCID MARGINAL CORNEAL DEGENERATION i s a
noninflammatory, corneal thinning disorder characterized by a crescent-shaped area of cor neal thinning extending from the 4 o'clock to the 8 o'clock meridians. The area of thinning usually measures approximately 1 to 2 mm in width and is separated from the corneoscleral limbus by 1 to 2 mm of normal-thickness cor nea. 1 In advanced cases the cornea protrudes just above the area of corneal thinning, produc ing a characteristic configuration on profile ex amination. 2 Photokeratographs typically show marked central corneal flattening along a verti cal meridian with marked steepening inferior ly.3 Irregular astigmatism is common and hard contact lenses are not usually tolerated in mod erate or advanced cases because of inferior decentration of the contact lenses.
Accepted for publication Dec. 10, 1991. From the Anterior Segment/External Disease Divi sion, King Khaled Eye Specialist Hospital, Riyadh, Saudi Arabia. Reprint requests to James A. Cameron, M.D., c/o Medical Library, King Khaled Eye Specialist Hospital, P.O. Box 7191, Riyadh 11462, Saudi Arabia.
296
Reports describing surgical treatments for pellucid marginal corneal degeneration are un common 412 and have usually been limited to isolated case reports with short follow-up.
Patients and Methods Five eyes of four consecutive patients had crescentic lamellar resection for pellucid mar ginal corneal degeneration and were followed up for more than two years. All patients were male. The ages of the patients at the time of surgery ranged from 16 to 36 years (mean, 24 years). Coexisting ocular conditions included inactive vernal conjunctivitis in two patients. One patient had crescentic deep corneal scars bilaterally in the area of corneal thinning. The procedures were performed between March 1987 and March 1989. All four patients had moderate to advanced pellucid marginal degen eration. Uncorrected visual acuity preoperatively ranged between 20/200 and counting fingers. Contact lenses could not be fitted in any of the patients because of inferior decentration. Spectacle correction was unsatisfactory be cause of the high astigmatic error and the pres ence of irregular astigmatism. Corneal abnor malities in the five eyes were limited to the peripheral inferior cornea. Traction sutures were placed through the episcleral tissue at the corneoscleral limbus at the 9 o'clock and 3 o'clock meridians to rotate the eye superiorly. Irregular astigmatism with marked flattening of the central cornea along the vertical meridian was confirmed by observ ing the corneal reflection from a round Flieringa ring held perpendicular to the cornea. With the patient seated at the slit lamp, the margins of the crescent to be resected were mapped on the cornea preoperatively on the day of surgery by using a bent 27-gauge needle to produce superficial punctures. With a guard ed diamond knife blade, a crescent-shaped inci sion to midstroma was made from the 4 o'clock
©AMERICAN JOURNAL OF OPHTHALMOLOGY 113:296-302, MARCH, 1992
Vol. 113, No. 3
Lamellar Crescentic Resection Keratoplasty
to 8 o'clock meridians on the cornea. The inci sion was made through normal-thickness cor nea approximately 1 mm from the corneoscleral limbus. Deeper stromal dissection to the area above Descemet's membrane was then contin ued with a less sharp blade. After reaching the desired depth, dissection was directed superi orly until normal-thickness cornea was reached. Fine scissors were used to excise the wedge of thinned cornea completing the cres centic resection. Stromal tissue at the base of the wedge was then undermined both interiorly and superiorly in preparation for suturing. Four 10-0 polypropylene sutures were passed through normal-thickness stroma interiorly and then through normal-thickness stroma su periorly at the plane where the tissue was previously undermined (Fig. 1). A paracentesis was then performed either through the corneo scleral limbus or with a needle tip through Descemet's membrane in the area of the resec tion. The intraocular pressure was reduced to allow closure and reapposition of normalthickness cornea to normal-thickness cornea. The four preplaced sutures were then tied with a triple-throw followed by two single-throws to complete the knot. Additional 10-0 polypropyl ene sutures were added to reapproximate the tissue. The total number of sutures numbered between ten and 15. Suture knots were rotated and buried in the corneal stroma. The corneal reflex from a Flieringa ring was then observed to ensure a reversal of the preoperative pattern so that a moderate amount of steepening of the central cornea along a vertical meridian (that is, with-the-rule astigmatism) was present at the end of the procedure. Postoperatively, the patients were treated with topical corticosteroid eyedrops, antibiotic eyedrops, and mydriatic eyedrops for the first month. Photokeratography and keratometry were done at each postoperative visit. Sutures
Fig. 1 (Cameron). Sutures reappose normal-thick ness stroma to normal-thickness stroma after cres cent has been resected.
297
were removed if they became loose. No sutures were intentionally removed before three months. If excessive central steepening along a vertical meridian remained after three months, selected sutures were cut and removed depend ing on the slit-lamp observations of tight su tures, the photokeratographic appearance of excessive compression from a suture, or both. Sutures were no longer cut once the desired visual result and photokeratographic pattern had been obtained. Adjacent sutures were not cut on the same day, and no more than two sutures were removed at one visit.
Case Reports Case 1 This 24-year-old man was first examined in October 1987 because of gradual progressive decrease in visual acuity in both eyes. The patient had previously received treatment for many years for vernal keratoconjunctivitis. Uncorrected visual acuity was R.E.: 20/200 and L.E.: 20/60. Slit-lamp examination showed bi lateral inferior crescents of corneal thinning from the 4 o'clock to 8 o'clock meridians situat ed approximately 1 mm from the corneoscleral limbus. There was forward protrusion of the cornea above the zone of corneal thinning (Fig. 2). Photokeratographs showed marked central corneal flattening along the vertical meridian with marked steepening interiorly (Fig. 3, left). Central keratometry reading of the right eye was 53 at 175/36 at 85. Spectacle-lens correc tion was unsatisfactory because of the high
Fig. 2 (Cameron). Case 1. Right eye, preoperatively has a 1-mm zone of corneal thinning approximately 1 mm from the corneoscleral limbus. There is forward protrusion of the cornea above the zone of thinning.
298
AMERICAN JOURNAL OF OPHTHALMOLOGY
March, 1992
Fig. 3 (Cameron). Case 1. Photokeratographs of the right eye. Preoperatively, irregular, against-the-rule astigmatism centrally with marked steepening inferiorly (left); 40 months after surgery marked reduction in central corneal astigmatism (right).
astigmatic error a n d i r r e g u l a r a s t i g m a t i s m . A h a r d contact lens i m p r o v e d visual acuity briefly to 2 0 / 3 0 in each eye; h o w e v e r , b e c a u s e of inferior d e c e n t r a t i o n in b o t h eyes, a c o n t a c t lens could not b e fitted. Lamellar crescentic resection was p e r f o r m e d on the r i g h t eye in April 1988. Fifteen 10-0 p o l y p r o p y l e n e s u t u r e s w e r e u s e d to r e a p p o s e n o r m a l - t h i c k n e s s c o r n e al s t r o m a to n o r m a l - t h i c k n e s s corneal s t r o m a (Fig. 4). Fifteen w e e k s after the o p e r a t i o n , two s u t u r e s were cut a n d r e m o v e d in an a t t e m p t to r e d u c e surgically i n d u c e d c e n t r a l corneal v e r t i cal s t e e p e n i n g (that is, w i t h - t h e - r u l e a s t i g m a tism). S u t u r e s w e r e t h e n u s u a l l y cut at m o n t h l y i n t e r v a l s in an a t t e m p t to r e d u c e a s t i g m a t i s m a n d p r o d u c e a spherical central p a t t e r n on the p h o t o k e r a t o g r a p h . K e r a t o m e t r y r e a d i n g s stabi lized n i n e m o n t h s after s u r g e r y , a n d visual acuity h a s b e e n m a i n t a i n e d at 2 0 / 2 5 w i t h a spectacle-lens correction of R.E.: + 0 . 7 5 —1.25 X 6 5 . The last k e r a t o m e t r y r e a d i n g was R.E.: 43 at 1 4 0 / 4 2 at 50. The p h o t o k e r a t o g r a p h at 40 m o n t h s after s u r g e r y s h o w e d a m a r k e d r e d u c tion in central corneal a s t i g m a t i s m (Fig. 3,
right). T h r e e p o l y p r o p y l e n e s u t u r e s r e m a i n in place a n d will r e m a i n indefinitely u n l e s s they loosen or b r e a k . Visual acuity in the left eye c o n t i n u e d to d e c r e a s e , a n d in March 1989 it was 2 0 / 2 0 0 . C e n t r a l k e r a t o m e t r y r e a d i n g was 49 at 1 8 0 / 4 0
Fig. 4 (Cameron). Case 1. Right eye one year after surgery. Most sutures have been removed. There is a more normal corneal configuration.
Vol. 113, No. 3
Lamellar Crescentic Resection Keratoplasty
at 90. A lamellar crescent resection was per formed on the left cornea in March 1989. A postoperative examination at eight weeks after surgery showed a marked superficial and midstromal pannus with mucus accumulation around loose sutures. A bandage contact lens was applied, and a short course of topical corticosteroids was tried in an attempt to reduce irritation and decrease stromal vascularization. Sutures were subsequently cut, and all sutures were removed by five months after surgery. Stromal blood vessels regressed after removal of the loose sutures. Uncorrected visual acuity was 20/50 seven months after the operation. Inferior corneal thinning and irregular againstthe-rule astigmatism gradually increased, and visual acuity gradually decreased to 20/200. The central keratometry reading 29 months after surgery was 50 at 180/36.5 at 90. The lamellar crescent procedure was repeated in this eye in August 1991. Case 2 This 16-year-old boy with inactive vernal keratoconjunctivitis had progressive decrease in visual acuity in both eyes. Uncorrected visu al acuity was R.E.: 20/100 and L.E.: counting fingers. Spectacle lenses did not significantly improve visual acuity, and hard contact lenses were unstable in both eyes. A crescent of inferi or corneal thinning concentric to the corneoscleral limbus was present bilaterally. Preoperative central keratometry of the left eye was 50.5 at 5/42 at 75. Lamellar crescentic resection was performed on the left cornea in September 1988. Six months after the resection visual acuity was 20/25 with a spectacle-lens correc tion of —5.25 —3.25 x 110. Twenty-seven months after the operation the patient was successfully wearing a hard contact lens and had a visual acuity of 2 0 / 2 5 . The last central keratometry reading was 49 at 10/46.5 at 105. Case 3 This 18-year-old man, first examined in Janu ary 1987, had bilateral progressive decrease in visual acuity. Visual acuity was counting fin gers in each eye. Spectacle lenses did not im prove his visual acuity because of irregular astigmatism, and contact lenses could not be fitted because of inferior decentration. Pellucid marginal corneal degeneration was present in both eyes. Central keratometry readings were R.E.: 53 at 175/39 at 85 and L.E.: 53 at 170/ 39.5 at 80. Lamellar crescentic resection was
299
performed on the left cornea in March 1987. Keratometry reading stabilized 5Vi months after surgery at 47.5 at 12/41 at 105 and remained unchanged for the next 31 months. Visual acu ity in the left eye 36 months after resection was 20/40 with a spectacle-lens correction of — 1.00 - 3 . 2 5 x 92. Case 4 This 36-year-old man had gradual, bilateral decrease in visual acuity in both eyes. Visual acuity was R.E.: 20/50 and L.E.: 20/200. Con tact lenses could not be fitted in either eye. A crescent of inferior corneal thinning extending from the 4 o'clock to 8 o'clock meridians was present in each eye. Crescent-shaped deep cor neal scars in the superior half of the zone of corneal thinning were present in both eyes. There was no history of hydrops, and there were no Descemet's membrane scrolls indica tive of hydrops. The preoperative central kera tometry reading of the left eye was 52 at 5/32.5 at 90. Lamellar crescentic resection was per formed on the left cornea in July 1988. Sutures were selectively cut beginning three months after surgery. Keratometry measurement stabi lized 11 months after resection at 44.5 at 70/44 at 150, and uncorrected visual acuity was 2 0 / 30, 27 months postoperatively.
Results Postoperative follow-up ranged from 27 to 40 months (mean, 31.8 months). A visual acuity of 20/40 or better was obtained in four of five eyes by using the patient's preferred method of correction. This consisted of spectacle lenses in two patients, a hard contact lens in one patient, and no correction in one patient. The time interval from the date of the resection until obtaining a stable visual acuity of 20/40 or better with consistent keratometry readings in the four successfully treated eyes ranged from 5.5 to 11 months (mean, 7.9 months). Average final keratometric astigmatism, excluding the one eye with treatment failure, was 2.62 diop ters (range, 0.5 to 6.5 diopters). Complications of the procedure were vascu larization of the inferior peripheral cornea in all patients and treatment failure with recurrence of corneal thinning and astigmatism in one patient. Superficial vascularization was most apparent in the area of the sutures extending 1 mm onto the cornea and occasionally centrally
300
AMERICAN JOURNAL OF OPHTHALMOLOGY
another 1 mm to the superior end of the suture tract. Mid-stroma vessels were seen in Case 1 (left eye) in combination with loose sutures. These vessels regressed after removal of the loose sutures. The one eye with treatment fail ure had the lamellar crescentic resection proce dure repeated in August 1991.
Discussion In 1957, Schlaeppi 13 used the term "pellu cid," meaning translucent, to describe the typi cal inferior corneal thinning pattern with ab sence of vascularization and lipid infiltration. Vascularization and scarring may develop, however, because of the sequelae from acute hydrops. 114 Corneal protrusion in this disorder occurs just above the area of corneal thinning. Deep, stromal, horizontal stress lines that dis appear with pressure on the cornea may also be present. Crescent-shaped, deep corneal scars in the area of corneal thinning may also be ob served in patients with no history of hydrops. 10 Histopathologic findings of the thinned cornea in this disorder have disclosed abnormalities in all layers of the cornea. 616 Pellucid marginal corneal degeneration has typically been de scribed as a condition affecting only the inferior corneal periphery. However, some patients may also have a separate zone of central corneal thinning 4,17 and, rarely, superior corneal thin ning18 in combination with inferior corneal thinning. Modern surgical procedures advocated for the treatment of pellucid marginal corneal de generation have included eccentric penetrating keratoplasty, 4 ' 616 crescentic lamellar keratoplasty,7,8 large-diameter epikeratoplasty, 9 fullthickness wedge resection, 1011 and lamellar crescentic resection. 1112 Surgical results have been reported with large-diameter eccentric corneal grafts for the treatment of pellucid marginal degeneration. 4 Other reports describ ing surgical results have either been isolated case reports 71012 with short follow-up or have been cases where the surgical technique, indi vidual results, and complications were not re ported. 11 Surgical treatment for pellucid marginal cor neal degeneration by a crescent-shaped keratectomy of the thinned cornea has been report ed. In 1962, Zucchini 19 reported full-thickness excision of the thinned area of one eye of one patient with pellucid marginal degeneration. In 1981, Francisco Barraquer 11 reported on lamel
March, 1992
lar crescentic resection performed on six eyes with resulting "satisfactory anatomical recon struction." Specific details regarding surgical technique, individual results, and complica tions were not reported in this preliminary report. In 1991, Duran, Rodriguez-Ares, and Torres12 reported the result of lamellar crescen tic resection performed on one eye with a fol low-up of seven months. The anatomic goal of the surgical procedure in the present series was to excise the abnormal crescent of thinned corneal stroma and then to reapproximate normal-thickness stroma to nor mal-thickness stroma. With a more normal cor neal configuration, visual improvement may then be possible with spectacle lenses or con tact lenses (Figs. 3 and 4). In the preoperative assessment of patients with pellucid marginal degeneration, the cen tral and superior cornea should be carefully observed to rule out a second zone of either central or superior corneal thinning. If this is present, consideration should be given to doing a large-diameter eccentric penetrating kerato plasty or large-diameter eccentric epikerato plasty as the preferred surgical procedure rath er than a crescent resection. The margins of the crescent to be excised are best marked preoperatively at the slit lamp because during the operation, without corneal markings, the limits of corneal thinning are not well visualized. Polypropylene sutures were used to reapproxi mate the corneal stroma. Monofilament nylon undergoes biodegradation after approximately one year, which results in loss of tensile strength and breakage. Because there have been no long-term results published for lamellar crescentic resection, polypropylene suture was chosen in the hope of preventing this reduction in tensile strength at one year with possible recurrence of the condition. Four preplaced sutures were positioned equidistant along the resected crescent. Sutures are easier to pass through the cornea with less tissue distortion while the globe is firm. After the paracentesis was performed, these four sutures were tied, and remaining polypropylene sutures were placed to reapproximate the edges of normalthickness corneal stroma. As the sutures are tied and the adjacent edges of the crescent are approximated, the initial sutures frequently be come loose and must be replaced. If a small corneal perforation were to occur during the dissection, the procedure should be continued. If a large perforation through Descemet's mem brane and endothelium should occur, then a full-thickness wedge resection of the crescent
Vol. 113, No. 3
Lamellar Crescentic Resection Keratoplasty
301
should be performed. Overcorrection of the astigmatism at the time of the procedure is important if a good visual result is to be ob tained. Troutman 20 advised an approximate 50% overcorrection for wedge resections when treating postkeratoplasty astigmatism. Barraquer 11 observed some loss of effect during the first year after lamellar crescent resection. In this series some loss of effect was noted by observing photokeratographs during the first three months. After this period sutures were selectively cut in an attempt to gradually reduce with-the-rule astigmatism. Complications of the surgical procedure were peripheral corneal vascularization in all pa tients and loss of effect caused by early loosen ing of all sutures in one patient. Vascularization is inevitable because of the close proximity of the incision and sutures to the corneoscleral limbus. No vessels extended more centrally than the superior suture tract. Mid-stromal ves sels with loose sutures were observed in one patient (Case 1, left eye). Vessels regressed after a short course of topical corticosteroid eyedrops and removal of the loose sutures. The reason for loose sutures in this patient was not known. Possibly one or two loose sutures may have been the inciting agent for stromal vascu larization with contraction of the wound and loosening of all sutures. Caldwell and associ ates21 observed loosening of sutures, which re quired reoperation in one of four patients with superior Terrien's marginal degeneration treat ed by lamellar crescentic resection.
abnormal area of the cornea, in contrast to large-diameter penetrating keratoplasty where most of the patient's cornea is replaced. The corneal incision with crescentic lamellar resec tion is smaller than with penetrating kerato plasty, and the anterior chamber is entered only by a small paracentesis. No donor tissue is used, thereby eliminating complications relat ed to donor material such as donor-to-host transmission of disease, 22,23 and graft rejection. Graft rejection is noticeably higher with largediameter penetrating keratoplasty because of close proximity to the limbal vasculature. Varley, Macsai, and Krachmer 4 reported allograft rejection in seven of 11 of their clear, largediameter grafts. Speaker, Arentsen, and Laibson 6 reported graft rejection episodes in eight of 15 eyes with large-diameter grafts. Potential complications of cataract and glaucoma associ ated with the long-term use of topical cortico steroid eyedrops to prevent graft rejection are avoided with crescentic lamellar resection. One possible disadvantage of crescentic lamellar resection is that visual acuity is usually poor for the first six months after surgery because of overcorrection and suture-induced irregular astigmatism. However, visual rehabilitation af ter penetrating keratoplasty is also frequently delayed until after the graft wound has healed and all sutures have been removed. 4
Long-term follow-up is necessary to assess the success of this surgical procedure. In an attempt to evaluate long-term success and sta bility, patients in the present series were only included if they had a follow-up of two or more years. Short-term follow-up may sometimes give misleading results. In Case 1 (left eye) with early loosening of sutures, the patient had an uncorrected visual acuity of 20/50 seven months after surgery. Twenty-nine months af ter surgery uncorrected visual acuity had dropped to 20/200, and inferior corneal thin ning with irregular against-the-rule astigma tism had returned. The other four patients maintained stable visual acuities and keratometry readings after an initial period of instability ranging from 5.5 to 11 months (mean, 7.9 months) postoperatively. Lamellar crescent resection has a number of advantages over large-diameter eccentric pene trating keratoplasty for the treatment of pellu cid marginal corneal degeneration. Treatment with crescentic resection is localized to the
1. Krachmer, J. H.: Pellucid marginal corneal de generation. Arch. Ophthalmol. 96:1217, 1978. 2. Maguire, L. J., and Meyer, R. F.: Ectatic corneal degenerations. In Kaufman, H. E., Barron, B. A., McDonald, M. B., and Waltman, S. R. (eds.): The Cornea. New York, Churchill Livingstone, 1988, pp. 498-499. 3. Maguire, L. J., Klyce, S. D., McDonald, M. B., and Kaufman, H. E.: Corneal topography of pellucid marginal degeneration. Ophthalmology 94:519, 1987. 4. Varley, G. A., Macsai, M. S., and Krachmer, J. H.: The results of penetrating keratoplasty for pellucid marginal corneal degeneration. Am. J. Oph thalmol. 110:149, 1990. 5. Pouliquen, Y., D'Hermies, F., Puech, M., Dhermy, P., Goichot-Bonnat, L., and Savoldelli, M.: Acute corneal edema in pellucid marginal degenera tion or acute marginal keratoconus. Cornea 6:169, 1987. 6. Speaker, M. G., Arentsen, J. J., and Laibson, P. R.: Long-term survival of large diameter penetrat ing keratoplasties for keratoconus and pellucid mar ginal degeneration. Acta Ophthalmol. (Copenh.) 192(suppl.):17, 1989.
References
302
AMERICAN JOURNAL OF OPHTHALMOLOGY
7. Hallerman, W.: Uber atypischen Keratokonus und andere konstitutionell-progressive Hornhautektasien. Klin. Monatsbl. Augenheilkd. 156:161, 1970. 8. Schanzlin, D. J., Sarno, E. M., and Robin, J. B.: Crescentic lamellar keratoplasty for pellucid margin al degeneration. Am. J. Ophthalmol. 96:253, 1983. 9. Fronterre, A., and Portesani, G. P.: Epikeratoplasty for pellucid marginal corneal degeneration. Cornea 10:450, 1991. 10. Dubroff, S.: Pellucid marginal corneal degen eration. Report on corrective surgery. J. Cataract Refract. Surg. 15:89, 1989. 11. Barraquer, F.: Results of the crescent resection in keratotorus. Dev. Ophthalmol. 5:49, 1981. 12. Duran, J. A., Rodriguez-Ares, M. T., and Tor res, D.: Crescentic resection for the treatment of pellucid corneal marginal degeneration. Ophthalmic Surg. 22:153, 1991. 13. Schlaeppi, V.: La dystrophie marginale inferieure pellucide de la cornee. Probl. Actuels Ophtalmol. 1:672, 1957. 14. Carter, J. B., Jones, D. B., and Wilhelmus, K. R.: Acute hydrops in pellucid marginal corneal degeneration. Am. J. Ophthalmol. 107:167, 1989. 15. Cameron, J. A.: Deep corneal scarring in pellu cid marginal corneal degeneration. Cornea, in press. 16. Parker, D. L., McDonnell, P. J., Barraquer, J.,
March, 1992
and Green, W. R.: Pellucid marginal corneal degen eration. Cornea 5:115, 1986. 17. Kayazawa, F., Nishimura, K., Kodama, Y., Tsuji, T., and Itoi, M.: Keratoconus with pellucid marginal corneal degeneration. Arch. Ophthalmol. 102:895, 1984. 18. Cameron, J. A., and Mahmood, M. A.: Superi or corneal thinning with pellucid marginal corneal degeneration. Am. J. Ophthalmol. 109:486, 1990. 19. Zucchini, G.: Su di un caso di degenerazione marginale della cornea-varieta' inferiore pellucidastudio clinico ed istologico. Ann. Ottalmol. Clin. Oculist. 88:47, 1962. 20. Troutman, R. C : Corneal wedge resections and relaxing incisions for postkeratoplasty astigma tism. Int. Ophthalmol. Clin. 23:161, 1983. 21. Caldwell, D. R., Insler, M. S., Boutros, G., and Hawk, T.: Primary surgical repair of severe peripher al marginal ectasia in Terrien's marginal degenera tion. Am. J. Ophthalmol. 97:332, 1984. 22. O'Day, D. M.: Diseases potentially transmitted through corneal transplantation. Ophthalmology 96:1133, 1989. 23. Cameron, J. A., Antonios, S. R., Cotter, J. B., and Habash, N. R.: Endophthalmitis from contami nated donor corneas following penetrating kerato plasty. Arch. Ophthalmol. 109:54, 1991.
OPHTHALMIC MINIATURE
He was a vigorous, ruddy, maxssive man with iron-gray hair, an iron-gray moustache, and hard, black eyes that must have seriously dented all the objects at which they aimed. The outside world was protected from these dangerous rays by u n r i m m e d bifocal glasses, doubtless crash-proof, since he levelled his glance straight at people as if he neither knew nor cared that it was loaded. Dawn Powell, A Time to be Born New York, Yarrow Press, 1991, pp. 207-208
Five eyes in four patients with pellucid marginal corneal degeneration were treated by lamellar crescentic resection of the thinned area inferiorly. Normal-thickness stroma was then reapposed to normal-thickness stroma with multiple interrupted 10-0 polypropylene sutures. If excessive central corneal steepen ing along a vertical meridian was present three months after surgery, selected sutures were cut and removed depending on the slitlamp appearance, keratometry reading, and photokeratograph pattern. Improvement of visual acuity to 20/40 or better was obtained in four of the five eyes with a follow-up of 27 to 40 months (mean, 31.8 months). Early loos ening of sutures resulted in a recurrence of corneal thinning and astigmatism in one eye. Fannus developed inferiorly in all five eyes. 1 ELLUCID MARGINAL CORNEAL DEGENERATION i s a
noninflammatory, corneal thinning disorder characterized by a crescent-shaped area of cor neal thinning extending from the 4 o'clock to the 8 o'clock meridians. The area of thinning usually measures approximately 1 to 2 mm in width and is separated from the corneoscleral limbus by 1 to 2 mm of normal-thickness cor nea. 1 In advanced cases the cornea protrudes just above the area of corneal thinning, produc ing a characteristic configuration on profile ex amination. 2 Photokeratographs typically show marked central corneal flattening along a verti cal meridian with marked steepening inferior ly.3 Irregular astigmatism is common and hard contact lenses are not usually tolerated in mod erate or advanced cases because of inferior decentration of the contact lenses.
Accepted for publication Dec. 10, 1991. From the Anterior Segment/External Disease Divi sion, King Khaled Eye Specialist Hospital, Riyadh, Saudi Arabia. Reprint requests to James A. Cameron, M.D., c/o Medical Library, King Khaled Eye Specialist Hospital, P.O. Box 7191, Riyadh 11462, Saudi Arabia.
296
Reports describing surgical treatments for pellucid marginal corneal degeneration are un common 412 and have usually been limited to isolated case reports with short follow-up.
Patients and Methods Five eyes of four consecutive patients had crescentic lamellar resection for pellucid mar ginal corneal degeneration and were followed up for more than two years. All patients were male. The ages of the patients at the time of surgery ranged from 16 to 36 years (mean, 24 years). Coexisting ocular conditions included inactive vernal conjunctivitis in two patients. One patient had crescentic deep corneal scars bilaterally in the area of corneal thinning. The procedures were performed between March 1987 and March 1989. All four patients had moderate to advanced pellucid marginal degen eration. Uncorrected visual acuity preoperatively ranged between 20/200 and counting fingers. Contact lenses could not be fitted in any of the patients because of inferior decentration. Spectacle correction was unsatisfactory be cause of the high astigmatic error and the pres ence of irregular astigmatism. Corneal abnor malities in the five eyes were limited to the peripheral inferior cornea. Traction sutures were placed through the episcleral tissue at the corneoscleral limbus at the 9 o'clock and 3 o'clock meridians to rotate the eye superiorly. Irregular astigmatism with marked flattening of the central cornea along the vertical meridian was confirmed by observ ing the corneal reflection from a round Flieringa ring held perpendicular to the cornea. With the patient seated at the slit lamp, the margins of the crescent to be resected were mapped on the cornea preoperatively on the day of surgery by using a bent 27-gauge needle to produce superficial punctures. With a guard ed diamond knife blade, a crescent-shaped inci sion to midstroma was made from the 4 o'clock
©AMERICAN JOURNAL OF OPHTHALMOLOGY 113:296-302, MARCH, 1992
Vol. 113, No. 3
Lamellar Crescentic Resection Keratoplasty
to 8 o'clock meridians on the cornea. The inci sion was made through normal-thickness cor nea approximately 1 mm from the corneoscleral limbus. Deeper stromal dissection to the area above Descemet's membrane was then contin ued with a less sharp blade. After reaching the desired depth, dissection was directed superi orly until normal-thickness cornea was reached. Fine scissors were used to excise the wedge of thinned cornea completing the cres centic resection. Stromal tissue at the base of the wedge was then undermined both interiorly and superiorly in preparation for suturing. Four 10-0 polypropylene sutures were passed through normal-thickness stroma interiorly and then through normal-thickness stroma su periorly at the plane where the tissue was previously undermined (Fig. 1). A paracentesis was then performed either through the corneo scleral limbus or with a needle tip through Descemet's membrane in the area of the resec tion. The intraocular pressure was reduced to allow closure and reapposition of normalthickness cornea to normal-thickness cornea. The four preplaced sutures were then tied with a triple-throw followed by two single-throws to complete the knot. Additional 10-0 polypropyl ene sutures were added to reapproximate the tissue. The total number of sutures numbered between ten and 15. Suture knots were rotated and buried in the corneal stroma. The corneal reflex from a Flieringa ring was then observed to ensure a reversal of the preoperative pattern so that a moderate amount of steepening of the central cornea along a vertical meridian (that is, with-the-rule astigmatism) was present at the end of the procedure. Postoperatively, the patients were treated with topical corticosteroid eyedrops, antibiotic eyedrops, and mydriatic eyedrops for the first month. Photokeratography and keratometry were done at each postoperative visit. Sutures
Fig. 1 (Cameron). Sutures reappose normal-thick ness stroma to normal-thickness stroma after cres cent has been resected.
297
were removed if they became loose. No sutures were intentionally removed before three months. If excessive central steepening along a vertical meridian remained after three months, selected sutures were cut and removed depend ing on the slit-lamp observations of tight su tures, the photokeratographic appearance of excessive compression from a suture, or both. Sutures were no longer cut once the desired visual result and photokeratographic pattern had been obtained. Adjacent sutures were not cut on the same day, and no more than two sutures were removed at one visit.
Case Reports Case 1 This 24-year-old man was first examined in October 1987 because of gradual progressive decrease in visual acuity in both eyes. The patient had previously received treatment for many years for vernal keratoconjunctivitis. Uncorrected visual acuity was R.E.: 20/200 and L.E.: 20/60. Slit-lamp examination showed bi lateral inferior crescents of corneal thinning from the 4 o'clock to 8 o'clock meridians situat ed approximately 1 mm from the corneoscleral limbus. There was forward protrusion of the cornea above the zone of corneal thinning (Fig. 2). Photokeratographs showed marked central corneal flattening along the vertical meridian with marked steepening interiorly (Fig. 3, left). Central keratometry reading of the right eye was 53 at 175/36 at 85. Spectacle-lens correc tion was unsatisfactory because of the high
Fig. 2 (Cameron). Case 1. Right eye, preoperatively has a 1-mm zone of corneal thinning approximately 1 mm from the corneoscleral limbus. There is forward protrusion of the cornea above the zone of thinning.
298
AMERICAN JOURNAL OF OPHTHALMOLOGY
March, 1992
Fig. 3 (Cameron). Case 1. Photokeratographs of the right eye. Preoperatively, irregular, against-the-rule astigmatism centrally with marked steepening inferiorly (left); 40 months after surgery marked reduction in central corneal astigmatism (right).
astigmatic error a n d i r r e g u l a r a s t i g m a t i s m . A h a r d contact lens i m p r o v e d visual acuity briefly to 2 0 / 3 0 in each eye; h o w e v e r , b e c a u s e of inferior d e c e n t r a t i o n in b o t h eyes, a c o n t a c t lens could not b e fitted. Lamellar crescentic resection was p e r f o r m e d on the r i g h t eye in April 1988. Fifteen 10-0 p o l y p r o p y l e n e s u t u r e s w e r e u s e d to r e a p p o s e n o r m a l - t h i c k n e s s c o r n e al s t r o m a to n o r m a l - t h i c k n e s s corneal s t r o m a (Fig. 4). Fifteen w e e k s after the o p e r a t i o n , two s u t u r e s were cut a n d r e m o v e d in an a t t e m p t to r e d u c e surgically i n d u c e d c e n t r a l corneal v e r t i cal s t e e p e n i n g (that is, w i t h - t h e - r u l e a s t i g m a tism). S u t u r e s w e r e t h e n u s u a l l y cut at m o n t h l y i n t e r v a l s in an a t t e m p t to r e d u c e a s t i g m a t i s m a n d p r o d u c e a spherical central p a t t e r n on the p h o t o k e r a t o g r a p h . K e r a t o m e t r y r e a d i n g s stabi lized n i n e m o n t h s after s u r g e r y , a n d visual acuity h a s b e e n m a i n t a i n e d at 2 0 / 2 5 w i t h a spectacle-lens correction of R.E.: + 0 . 7 5 —1.25 X 6 5 . The last k e r a t o m e t r y r e a d i n g was R.E.: 43 at 1 4 0 / 4 2 at 50. The p h o t o k e r a t o g r a p h at 40 m o n t h s after s u r g e r y s h o w e d a m a r k e d r e d u c tion in central corneal a s t i g m a t i s m (Fig. 3,
right). T h r e e p o l y p r o p y l e n e s u t u r e s r e m a i n in place a n d will r e m a i n indefinitely u n l e s s they loosen or b r e a k . Visual acuity in the left eye c o n t i n u e d to d e c r e a s e , a n d in March 1989 it was 2 0 / 2 0 0 . C e n t r a l k e r a t o m e t r y r e a d i n g was 49 at 1 8 0 / 4 0
Fig. 4 (Cameron). Case 1. Right eye one year after surgery. Most sutures have been removed. There is a more normal corneal configuration.
Vol. 113, No. 3
Lamellar Crescentic Resection Keratoplasty
at 90. A lamellar crescent resection was per formed on the left cornea in March 1989. A postoperative examination at eight weeks after surgery showed a marked superficial and midstromal pannus with mucus accumulation around loose sutures. A bandage contact lens was applied, and a short course of topical corticosteroids was tried in an attempt to reduce irritation and decrease stromal vascularization. Sutures were subsequently cut, and all sutures were removed by five months after surgery. Stromal blood vessels regressed after removal of the loose sutures. Uncorrected visual acuity was 20/50 seven months after the operation. Inferior corneal thinning and irregular againstthe-rule astigmatism gradually increased, and visual acuity gradually decreased to 20/200. The central keratometry reading 29 months after surgery was 50 at 180/36.5 at 90. The lamellar crescent procedure was repeated in this eye in August 1991. Case 2 This 16-year-old boy with inactive vernal keratoconjunctivitis had progressive decrease in visual acuity in both eyes. Uncorrected visu al acuity was R.E.: 20/100 and L.E.: counting fingers. Spectacle lenses did not significantly improve visual acuity, and hard contact lenses were unstable in both eyes. A crescent of inferi or corneal thinning concentric to the corneoscleral limbus was present bilaterally. Preoperative central keratometry of the left eye was 50.5 at 5/42 at 75. Lamellar crescentic resection was performed on the left cornea in September 1988. Six months after the resection visual acuity was 20/25 with a spectacle-lens correc tion of —5.25 —3.25 x 110. Twenty-seven months after the operation the patient was successfully wearing a hard contact lens and had a visual acuity of 2 0 / 2 5 . The last central keratometry reading was 49 at 10/46.5 at 105. Case 3 This 18-year-old man, first examined in Janu ary 1987, had bilateral progressive decrease in visual acuity. Visual acuity was counting fin gers in each eye. Spectacle lenses did not im prove his visual acuity because of irregular astigmatism, and contact lenses could not be fitted because of inferior decentration. Pellucid marginal corneal degeneration was present in both eyes. Central keratometry readings were R.E.: 53 at 175/39 at 85 and L.E.: 53 at 170/ 39.5 at 80. Lamellar crescentic resection was
299
performed on the left cornea in March 1987. Keratometry reading stabilized 5Vi months after surgery at 47.5 at 12/41 at 105 and remained unchanged for the next 31 months. Visual acu ity in the left eye 36 months after resection was 20/40 with a spectacle-lens correction of — 1.00 - 3 . 2 5 x 92. Case 4 This 36-year-old man had gradual, bilateral decrease in visual acuity in both eyes. Visual acuity was R.E.: 20/50 and L.E.: 20/200. Con tact lenses could not be fitted in either eye. A crescent of inferior corneal thinning extending from the 4 o'clock to 8 o'clock meridians was present in each eye. Crescent-shaped deep cor neal scars in the superior half of the zone of corneal thinning were present in both eyes. There was no history of hydrops, and there were no Descemet's membrane scrolls indica tive of hydrops. The preoperative central kera tometry reading of the left eye was 52 at 5/32.5 at 90. Lamellar crescentic resection was per formed on the left cornea in July 1988. Sutures were selectively cut beginning three months after surgery. Keratometry measurement stabi lized 11 months after resection at 44.5 at 70/44 at 150, and uncorrected visual acuity was 2 0 / 30, 27 months postoperatively.
Results Postoperative follow-up ranged from 27 to 40 months (mean, 31.8 months). A visual acuity of 20/40 or better was obtained in four of five eyes by using the patient's preferred method of correction. This consisted of spectacle lenses in two patients, a hard contact lens in one patient, and no correction in one patient. The time interval from the date of the resection until obtaining a stable visual acuity of 20/40 or better with consistent keratometry readings in the four successfully treated eyes ranged from 5.5 to 11 months (mean, 7.9 months). Average final keratometric astigmatism, excluding the one eye with treatment failure, was 2.62 diop ters (range, 0.5 to 6.5 diopters). Complications of the procedure were vascu larization of the inferior peripheral cornea in all patients and treatment failure with recurrence of corneal thinning and astigmatism in one patient. Superficial vascularization was most apparent in the area of the sutures extending 1 mm onto the cornea and occasionally centrally
300
AMERICAN JOURNAL OF OPHTHALMOLOGY
another 1 mm to the superior end of the suture tract. Mid-stroma vessels were seen in Case 1 (left eye) in combination with loose sutures. These vessels regressed after removal of the loose sutures. The one eye with treatment fail ure had the lamellar crescentic resection proce dure repeated in August 1991.
Discussion In 1957, Schlaeppi 13 used the term "pellu cid," meaning translucent, to describe the typi cal inferior corneal thinning pattern with ab sence of vascularization and lipid infiltration. Vascularization and scarring may develop, however, because of the sequelae from acute hydrops. 114 Corneal protrusion in this disorder occurs just above the area of corneal thinning. Deep, stromal, horizontal stress lines that dis appear with pressure on the cornea may also be present. Crescent-shaped, deep corneal scars in the area of corneal thinning may also be ob served in patients with no history of hydrops. 10 Histopathologic findings of the thinned cornea in this disorder have disclosed abnormalities in all layers of the cornea. 616 Pellucid marginal corneal degeneration has typically been de scribed as a condition affecting only the inferior corneal periphery. However, some patients may also have a separate zone of central corneal thinning 4,17 and, rarely, superior corneal thin ning18 in combination with inferior corneal thinning. Modern surgical procedures advocated for the treatment of pellucid marginal corneal de generation have included eccentric penetrating keratoplasty, 4 ' 616 crescentic lamellar keratoplasty,7,8 large-diameter epikeratoplasty, 9 fullthickness wedge resection, 1011 and lamellar crescentic resection. 1112 Surgical results have been reported with large-diameter eccentric corneal grafts for the treatment of pellucid marginal degeneration. 4 Other reports describ ing surgical results have either been isolated case reports 71012 with short follow-up or have been cases where the surgical technique, indi vidual results, and complications were not re ported. 11 Surgical treatment for pellucid marginal cor neal degeneration by a crescent-shaped keratectomy of the thinned cornea has been report ed. In 1962, Zucchini 19 reported full-thickness excision of the thinned area of one eye of one patient with pellucid marginal degeneration. In 1981, Francisco Barraquer 11 reported on lamel
March, 1992
lar crescentic resection performed on six eyes with resulting "satisfactory anatomical recon struction." Specific details regarding surgical technique, individual results, and complica tions were not reported in this preliminary report. In 1991, Duran, Rodriguez-Ares, and Torres12 reported the result of lamellar crescen tic resection performed on one eye with a fol low-up of seven months. The anatomic goal of the surgical procedure in the present series was to excise the abnormal crescent of thinned corneal stroma and then to reapproximate normal-thickness stroma to nor mal-thickness stroma. With a more normal cor neal configuration, visual improvement may then be possible with spectacle lenses or con tact lenses (Figs. 3 and 4). In the preoperative assessment of patients with pellucid marginal degeneration, the cen tral and superior cornea should be carefully observed to rule out a second zone of either central or superior corneal thinning. If this is present, consideration should be given to doing a large-diameter eccentric penetrating kerato plasty or large-diameter eccentric epikerato plasty as the preferred surgical procedure rath er than a crescent resection. The margins of the crescent to be excised are best marked preoperatively at the slit lamp because during the operation, without corneal markings, the limits of corneal thinning are not well visualized. Polypropylene sutures were used to reapproxi mate the corneal stroma. Monofilament nylon undergoes biodegradation after approximately one year, which results in loss of tensile strength and breakage. Because there have been no long-term results published for lamellar crescentic resection, polypropylene suture was chosen in the hope of preventing this reduction in tensile strength at one year with possible recurrence of the condition. Four preplaced sutures were positioned equidistant along the resected crescent. Sutures are easier to pass through the cornea with less tissue distortion while the globe is firm. After the paracentesis was performed, these four sutures were tied, and remaining polypropylene sutures were placed to reapproximate the edges of normalthickness corneal stroma. As the sutures are tied and the adjacent edges of the crescent are approximated, the initial sutures frequently be come loose and must be replaced. If a small corneal perforation were to occur during the dissection, the procedure should be continued. If a large perforation through Descemet's mem brane and endothelium should occur, then a full-thickness wedge resection of the crescent
Vol. 113, No. 3
Lamellar Crescentic Resection Keratoplasty
301
should be performed. Overcorrection of the astigmatism at the time of the procedure is important if a good visual result is to be ob tained. Troutman 20 advised an approximate 50% overcorrection for wedge resections when treating postkeratoplasty astigmatism. Barraquer 11 observed some loss of effect during the first year after lamellar crescent resection. In this series some loss of effect was noted by observing photokeratographs during the first three months. After this period sutures were selectively cut in an attempt to gradually reduce with-the-rule astigmatism. Complications of the surgical procedure were peripheral corneal vascularization in all pa tients and loss of effect caused by early loosen ing of all sutures in one patient. Vascularization is inevitable because of the close proximity of the incision and sutures to the corneoscleral limbus. No vessels extended more centrally than the superior suture tract. Mid-stromal ves sels with loose sutures were observed in one patient (Case 1, left eye). Vessels regressed after a short course of topical corticosteroid eyedrops and removal of the loose sutures. The reason for loose sutures in this patient was not known. Possibly one or two loose sutures may have been the inciting agent for stromal vascu larization with contraction of the wound and loosening of all sutures. Caldwell and associ ates21 observed loosening of sutures, which re quired reoperation in one of four patients with superior Terrien's marginal degeneration treat ed by lamellar crescentic resection.
abnormal area of the cornea, in contrast to large-diameter penetrating keratoplasty where most of the patient's cornea is replaced. The corneal incision with crescentic lamellar resec tion is smaller than with penetrating kerato plasty, and the anterior chamber is entered only by a small paracentesis. No donor tissue is used, thereby eliminating complications relat ed to donor material such as donor-to-host transmission of disease, 22,23 and graft rejection. Graft rejection is noticeably higher with largediameter penetrating keratoplasty because of close proximity to the limbal vasculature. Varley, Macsai, and Krachmer 4 reported allograft rejection in seven of 11 of their clear, largediameter grafts. Speaker, Arentsen, and Laibson 6 reported graft rejection episodes in eight of 15 eyes with large-diameter grafts. Potential complications of cataract and glaucoma associ ated with the long-term use of topical cortico steroid eyedrops to prevent graft rejection are avoided with crescentic lamellar resection. One possible disadvantage of crescentic lamellar resection is that visual acuity is usually poor for the first six months after surgery because of overcorrection and suture-induced irregular astigmatism. However, visual rehabilitation af ter penetrating keratoplasty is also frequently delayed until after the graft wound has healed and all sutures have been removed. 4
Long-term follow-up is necessary to assess the success of this surgical procedure. In an attempt to evaluate long-term success and sta bility, patients in the present series were only included if they had a follow-up of two or more years. Short-term follow-up may sometimes give misleading results. In Case 1 (left eye) with early loosening of sutures, the patient had an uncorrected visual acuity of 20/50 seven months after surgery. Twenty-nine months af ter surgery uncorrected visual acuity had dropped to 20/200, and inferior corneal thin ning with irregular against-the-rule astigma tism had returned. The other four patients maintained stable visual acuities and keratometry readings after an initial period of instability ranging from 5.5 to 11 months (mean, 7.9 months) postoperatively. Lamellar crescent resection has a number of advantages over large-diameter eccentric pene trating keratoplasty for the treatment of pellu cid marginal corneal degeneration. Treatment with crescentic resection is localized to the
1. Krachmer, J. H.: Pellucid marginal corneal de generation. Arch. Ophthalmol. 96:1217, 1978. 2. Maguire, L. J., and Meyer, R. F.: Ectatic corneal degenerations. In Kaufman, H. E., Barron, B. A., McDonald, M. B., and Waltman, S. R. (eds.): The Cornea. New York, Churchill Livingstone, 1988, pp. 498-499. 3. Maguire, L. J., Klyce, S. D., McDonald, M. B., and Kaufman, H. E.: Corneal topography of pellucid marginal degeneration. Ophthalmology 94:519, 1987. 4. Varley, G. A., Macsai, M. S., and Krachmer, J. H.: The results of penetrating keratoplasty for pellucid marginal corneal degeneration. Am. J. Oph thalmol. 110:149, 1990. 5. Pouliquen, Y., D'Hermies, F., Puech, M., Dhermy, P., Goichot-Bonnat, L., and Savoldelli, M.: Acute corneal edema in pellucid marginal degenera tion or acute marginal keratoconus. Cornea 6:169, 1987. 6. Speaker, M. G., Arentsen, J. J., and Laibson, P. R.: Long-term survival of large diameter penetrat ing keratoplasties for keratoconus and pellucid mar ginal degeneration. Acta Ophthalmol. (Copenh.) 192(suppl.):17, 1989.
References
302
AMERICAN JOURNAL OF OPHTHALMOLOGY
7. Hallerman, W.: Uber atypischen Keratokonus und andere konstitutionell-progressive Hornhautektasien. Klin. Monatsbl. Augenheilkd. 156:161, 1970. 8. Schanzlin, D. J., Sarno, E. M., and Robin, J. B.: Crescentic lamellar keratoplasty for pellucid margin al degeneration. Am. J. Ophthalmol. 96:253, 1983. 9. Fronterre, A., and Portesani, G. P.: Epikeratoplasty for pellucid marginal corneal degeneration. Cornea 10:450, 1991. 10. Dubroff, S.: Pellucid marginal corneal degen eration. Report on corrective surgery. J. Cataract Refract. Surg. 15:89, 1989. 11. Barraquer, F.: Results of the crescent resection in keratotorus. Dev. Ophthalmol. 5:49, 1981. 12. Duran, J. A., Rodriguez-Ares, M. T., and Tor res, D.: Crescentic resection for the treatment of pellucid corneal marginal degeneration. Ophthalmic Surg. 22:153, 1991. 13. Schlaeppi, V.: La dystrophie marginale inferieure pellucide de la cornee. Probl. Actuels Ophtalmol. 1:672, 1957. 14. Carter, J. B., Jones, D. B., and Wilhelmus, K. R.: Acute hydrops in pellucid marginal corneal degeneration. Am. J. Ophthalmol. 107:167, 1989. 15. Cameron, J. A.: Deep corneal scarring in pellu cid marginal corneal degeneration. Cornea, in press. 16. Parker, D. L., McDonnell, P. J., Barraquer, J.,
March, 1992
and Green, W. R.: Pellucid marginal corneal degen eration. Cornea 5:115, 1986. 17. Kayazawa, F., Nishimura, K., Kodama, Y., Tsuji, T., and Itoi, M.: Keratoconus with pellucid marginal corneal degeneration. Arch. Ophthalmol. 102:895, 1984. 18. Cameron, J. A., and Mahmood, M. A.: Superi or corneal thinning with pellucid marginal corneal degeneration. Am. J. Ophthalmol. 109:486, 1990. 19. Zucchini, G.: Su di un caso di degenerazione marginale della cornea-varieta' inferiore pellucidastudio clinico ed istologico. Ann. Ottalmol. Clin. Oculist. 88:47, 1962. 20. Troutman, R. C : Corneal wedge resections and relaxing incisions for postkeratoplasty astigma tism. Int. Ophthalmol. Clin. 23:161, 1983. 21. Caldwell, D. R., Insler, M. S., Boutros, G., and Hawk, T.: Primary surgical repair of severe peripher al marginal ectasia in Terrien's marginal degenera tion. Am. J. Ophthalmol. 97:332, 1984. 22. O'Day, D. M.: Diseases potentially transmitted through corneal transplantation. Ophthalmology 96:1133, 1989. 23. Cameron, J. A., Antonios, S. R., Cotter, J. B., and Habash, N. R.: Endophthalmitis from contami nated donor corneas following penetrating kerato plasty. Arch. Ophthalmol. 109:54, 1991.
OPHTHALMIC MINIATURE
He was a vigorous, ruddy, maxssive man with iron-gray hair, an iron-gray moustache, and hard, black eyes that must have seriously dented all the objects at which they aimed. The outside world was protected from these dangerous rays by u n r i m m e d bifocal glasses, doubtless crash-proof, since he levelled his glance straight at people as if he neither knew nor cared that it was loaded. Dawn Powell, A Time to be Born New York, Yarrow Press, 1991, pp. 207-208
