CONSULTATION SECTION: REFRACTIVE
predictability, and stability than LASIK and PRK and to have less risk for retinal detachment than RLE.9 Alain Saad, MD Damien Gatinel, MD Paris, France
REFERENCES 1. Khachikian SS, Belin MW, Ciolino JB. Intrasubject corneal thickness asymmetry. J Refract Surg 2008; 24:606–609 2. Saad A, Guilbert E, Gatinel D. Corneal enantiomorphism in normal and keratoconic eyes. J Refract Surg 2014; 30:542–547 3. Saad A, Gatinel D. Bilateral corneal ectasia after laser in situ keratomileusis in patient with isolated difference in central corneal thickness between eyes. J Cataract Refract Surg 2010; 36:1033–1035 4. Reinstein DZ, Archer TJ, Gobbe M. Corneal epithelial thickness profile in the diagnosis of keratoconus. J Refract Surg 2009; 25:604–610 5. Randleman JB, Trattler WB, Stulting RD. Validation of the Ectasia Risk Score System for preoperative laser in situ keratomileusis screening. Am J Ophthalmol 2008; 145:813–818 6. Santhiago MR, Smadja D, Gomes BF, Mello GR, Monteiro ML, Wilson SE, Randleman BJ. Association between the percent tissue altered and post-laser in situ keratomileusis ectasia in eyes with normal preoperative topography. Am J Ophthalmol 2014; 158:87–95 7. Katz T, Wagenfeld L, Galambos P, Darrelmann BG, Richard G, Linke SJ. LASIK versus photorefractive keratectomy for high myopic (O 3 diopter) astigmatism. J Refract Surg 2013; 29:824–831 8. Guedj M, Saad A, Audureau E, Gatinel D. Photorefractive keratectomy in patients with suspected keratoconus: five-year follow-up. J Cataract Refract Surg 2013; 39:66–73 9. Huang D, Schallhorn SC, Sugar A, Farjo AA, Majmudar PA, Trattler WB, Tanzer DJ. Phakic intraocular lens implantation for the correction of myopia; a report by the American Academy of Ophthalmology (Ophthalmic Technology Assessment). Ophthalmology 2009; 116:2244–2258. Available at: http:// www.brightonvisioncenter.com/Research/Phakic_IOLs_for_ Correction_of_Myopia_2009.pdf. Accessed May 13, 2015
- This patient's cornea is neither ectatic nor preectatic. The patient presents with symmetric astigmatism with no signs of irregularity and without increased K values. The posterior corneal elevation maps of both eyes show a slight but not significant irregularity. The thinnest point of the cornea in both eyes is almost centered. Because of the thin cornea, I do not recommend LASIK or surface ablation. If we perform LASIK, we would not respect the proposed lower RSB thickness to maintain the biomechanical properties of the cornea. In our clinic, we prefer to leave at least 300 mm of RSB for LASIK and 400 to 420 mm of the total cornea after surface ablation. Because this patient has no marked contact lenses intolerance, my first advice would be to use the contact
1329
lenses more frequently. If she insists on having refractive surgery and understands the procedure's risks, the best option is implantation of a toric posterior chamber pIOL. The ACD in both eyes is within the recommended limits for implantation of pIOLs, which would preserve the eyes' accommodation. Using US biomicroscopy, I would study the anatomy of the sulcus and search for a correlation between the white-to-white and sulcus-to-sulcus distances to preclude postoperative surprises with vaulting. In summary, it is advisable to increase contact lens use as the first choice for this patient. If she still prefers to have refractive surgery, I would implant a toric pIOL to leave the cornea untouched and obtain the optimum correction of the ametropia. María Jose Cosentino, MD Buenos Aires, Argentina
- The treatment of thin corneas in refractive surgery has been the subject of debate, mainly because of the increased incidence of postoperative ectatic disorders in these corneas (eg, post-LASIK ectasia) and the possible conversion of a subclinical keratoconic state to a clinical keratoconic manifestation. The thin cornea is not apparently a weak cornea; however, there are limits to how much tissue we can ablate and how much biomechanically active corneal tissue we can leave intact after corneal refractive surgery. Even in patients over the age of 35 years (when natural corneal crosslinking occurs), post-LASIK ectasia cases have been reported in treatments of highly myopic, healthy, thin corneas.1,2 The minimum limit of 250 mm of RSB is under dispute, and many surgeons prefer to convert from LASIK to surface ablation procedures (eg, PRK) in such cases. On the other hand, there are also limitations to PRK in eyes with very thin corneas when leaving the post-PRK corneal stroma at approximately 300 mm. (The retreatment options are limited in cases of haze formation, overcorrection, or undercorrection.) In the current case, the eyes seem to have healthy corneas with normal corneal topography; however, the low preoperative corneal pachymetry and high refractive error are relevant contraindications to refractive surgery. My first approach would be to deemphasize the need for surgical intervention and to advise the patient to convert from spectacles to contact lenses. There is no need to treat every myopic patient with refractive surgery, especially a patient at the prepresbyopic age of 38 years. The theoretically predicted RSB thickness of 260 mm is critically low for a LASIK procedure, and I would not proceed directly to LASIK because my personal
J CATARACT REFRACT SURG - VOL 41, JUNE 2015
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CONSULTATION SECTION: REFRACTIVE
RSB thickness safety limit is 300 mm. Female patients should be carefully selected for refractive surgery because should they become pregnant in the future, it could trigger post-LASIK corneal ectasia. The corneal refraction procedure that seems more suitable for the current refractive case is PRK. The high manifest refraction of the patient could contribute to intraoperative and postoperative complications (eg, myopic regression, corneal haze, overtreatment, and undertreatment). These are difficult to address in cases involving a very thin post-PRK cornea; the post-PRK residual stromal thickness should be at least 300 mm because if it were thinner, the options for retreatment would be limited. Alternatively, with this type of case I might take an intraocular treatment approach. Refractive lens exchange (using a toric IOL) could not be a solution for a myopic patient of this age because the risk for retinal detachment is high. Another possible solution is implantation of a pIOL in the posterior chamber, which has the advantage of maintaining accommodation. In the current case, the patient is not tolerating spectacles and the ACD measurements indicate that a posterior chamber pIOL (correcting myopia and astigmatism) could be implanted safely. However, the possibility of early cataract formation and the need for repeating surgery for pIOL extraction and cataract in the near future (in a 38-year-old patient) should be considered. In conclusion, in the current case I would prefer not to perform refractive surgery. The proper contact lens use seems the most preferable decision for this patient because of her age, the thin corneas, and the high attempted correction. If the patient remained highly motivated for refractive surgery, I would probably refer her to another refractive surgeon. George D. Kymionis, MD, PhD Heraklion, Crete, Greece
REFERENCES 1. Elsheikh A, Wang D, Brown M, Rama P, Campanelli M, Pye D. Assessment of corneal biomechanical properties and their variation with age. Curr Eye Res 2007; 32:11–19 JL, Vega-Estrada A, Baviera J, Beltra n J, Cobo2. Brenner LF, Alio Soriano R. Clinical grading of post-LASIK ectasia related to visual limitation and predictive factors for vision loss. J Cataract Refract Surg 2012; 38:1817–1826
- In my opinion, the best option in this case is implantation of a toric pIOL. The cornea is thin and has no existing or suspected keratoconus or other corneal ectasia, as supported by the topography, tomography, and OCT examinations. When the CCT is less than 500 mm, I
always perform PRK instead of LASIK, even when using a femtosecond laser to create a predictably thin flap. Moreover, I do not perform laser treatment if the CCT is less than 450 mm. To keep the post-LASIK risk low, I require an RSB of at least 300 mm (not 250 mm) and a total corneal thickness of at least 400 mm. I would not perform laser treatment in this case because the measurements are outside those requirements. For patients 21 to 50 years old, my inclination is to use pIOLs instead of RLE because of the increased risk for retinal damage or retinal detachment. For patients older than 50 years, I am inclined to replace the lens, and in some cases involving high myopia, monovision is a good alternative to multifocal IOLs. In this case, the ACD in the right eye is 3.38 mm and in the left eye is 3.41 mm. Both eyes are over the 3.0 mm requirement to implant safely an iris-fixated or posterior chamber pIOL. Another important condition for pIOL implantation is an endothelial cell count (ECC) of over 2000 cells/mm2; thus, an ECC should be performed before making the final decision in this case. Miguel Srur, MD Santiago, Chile EDITOR’S COMMENT This is an interesting, well-documented case that presents a thin cornea but normal results from other examinations performed using different technologies, including symmetric bow-tie pattern WTR Placido topography with normal regional relative thickness profiles obtained with tomography.1 Based on the data, some surgeons consider that this could be a normal thin cornea or a sign of pre-topographic ectatic disease. Many also consider that even if it is normal, a cornea this thin is very close to a higher risk level for the percentage of tissue altered, which has been shown to be a robust risk factor for post-LASIK ectasia.2–4 All respondents note that the risk factorsda potentially high percentage of tissue altered and a cornea more than 3 standard deviations thinner the normaldare enough to preclude LASIK, even with the more predictable flaps with modern microkeratomes and femtosecond lasers. Some respondents consider surface ablation a reasonable option, especially considering the patient's age. If the patient were younger than 30 years, even surface ablation might not be an option because this patient could still present some topographic signs of an ectatic disease.1 Other approaches discussed include small-incision lenticule extraction,5 which theoretically has less biomechanical impact, and a toric posterior
J CATARACT REFRACT SURG - VOL 41, JUNE 2015
predictability, and stability than LASIK and PRK and to have less risk for retinal detachment than RLE.9 Alain Saad, MD Damien Gatinel, MD Paris, France
REFERENCES 1. Khachikian SS, Belin MW, Ciolino JB. Intrasubject corneal thickness asymmetry. J Refract Surg 2008; 24:606–609 2. Saad A, Guilbert E, Gatinel D. Corneal enantiomorphism in normal and keratoconic eyes. J Refract Surg 2014; 30:542–547 3. Saad A, Gatinel D. Bilateral corneal ectasia after laser in situ keratomileusis in patient with isolated difference in central corneal thickness between eyes. J Cataract Refract Surg 2010; 36:1033–1035 4. Reinstein DZ, Archer TJ, Gobbe M. Corneal epithelial thickness profile in the diagnosis of keratoconus. J Refract Surg 2009; 25:604–610 5. Randleman JB, Trattler WB, Stulting RD. Validation of the Ectasia Risk Score System for preoperative laser in situ keratomileusis screening. Am J Ophthalmol 2008; 145:813–818 6. Santhiago MR, Smadja D, Gomes BF, Mello GR, Monteiro ML, Wilson SE, Randleman BJ. Association between the percent tissue altered and post-laser in situ keratomileusis ectasia in eyes with normal preoperative topography. Am J Ophthalmol 2014; 158:87–95 7. Katz T, Wagenfeld L, Galambos P, Darrelmann BG, Richard G, Linke SJ. LASIK versus photorefractive keratectomy for high myopic (O 3 diopter) astigmatism. J Refract Surg 2013; 29:824–831 8. Guedj M, Saad A, Audureau E, Gatinel D. Photorefractive keratectomy in patients with suspected keratoconus: five-year follow-up. J Cataract Refract Surg 2013; 39:66–73 9. Huang D, Schallhorn SC, Sugar A, Farjo AA, Majmudar PA, Trattler WB, Tanzer DJ. Phakic intraocular lens implantation for the correction of myopia; a report by the American Academy of Ophthalmology (Ophthalmic Technology Assessment). Ophthalmology 2009; 116:2244–2258. Available at: http:// www.brightonvisioncenter.com/Research/Phakic_IOLs_for_ Correction_of_Myopia_2009.pdf. Accessed May 13, 2015
- This patient's cornea is neither ectatic nor preectatic. The patient presents with symmetric astigmatism with no signs of irregularity and without increased K values. The posterior corneal elevation maps of both eyes show a slight but not significant irregularity. The thinnest point of the cornea in both eyes is almost centered. Because of the thin cornea, I do not recommend LASIK or surface ablation. If we perform LASIK, we would not respect the proposed lower RSB thickness to maintain the biomechanical properties of the cornea. In our clinic, we prefer to leave at least 300 mm of RSB for LASIK and 400 to 420 mm of the total cornea after surface ablation. Because this patient has no marked contact lenses intolerance, my first advice would be to use the contact
1329
lenses more frequently. If she insists on having refractive surgery and understands the procedure's risks, the best option is implantation of a toric posterior chamber pIOL. The ACD in both eyes is within the recommended limits for implantation of pIOLs, which would preserve the eyes' accommodation. Using US biomicroscopy, I would study the anatomy of the sulcus and search for a correlation between the white-to-white and sulcus-to-sulcus distances to preclude postoperative surprises with vaulting. In summary, it is advisable to increase contact lens use as the first choice for this patient. If she still prefers to have refractive surgery, I would implant a toric pIOL to leave the cornea untouched and obtain the optimum correction of the ametropia. María Jose Cosentino, MD Buenos Aires, Argentina
- The treatment of thin corneas in refractive surgery has been the subject of debate, mainly because of the increased incidence of postoperative ectatic disorders in these corneas (eg, post-LASIK ectasia) and the possible conversion of a subclinical keratoconic state to a clinical keratoconic manifestation. The thin cornea is not apparently a weak cornea; however, there are limits to how much tissue we can ablate and how much biomechanically active corneal tissue we can leave intact after corneal refractive surgery. Even in patients over the age of 35 years (when natural corneal crosslinking occurs), post-LASIK ectasia cases have been reported in treatments of highly myopic, healthy, thin corneas.1,2 The minimum limit of 250 mm of RSB is under dispute, and many surgeons prefer to convert from LASIK to surface ablation procedures (eg, PRK) in such cases. On the other hand, there are also limitations to PRK in eyes with very thin corneas when leaving the post-PRK corneal stroma at approximately 300 mm. (The retreatment options are limited in cases of haze formation, overcorrection, or undercorrection.) In the current case, the eyes seem to have healthy corneas with normal corneal topography; however, the low preoperative corneal pachymetry and high refractive error are relevant contraindications to refractive surgery. My first approach would be to deemphasize the need for surgical intervention and to advise the patient to convert from spectacles to contact lenses. There is no need to treat every myopic patient with refractive surgery, especially a patient at the prepresbyopic age of 38 years. The theoretically predicted RSB thickness of 260 mm is critically low for a LASIK procedure, and I would not proceed directly to LASIK because my personal
J CATARACT REFRACT SURG - VOL 41, JUNE 2015
1330
CONSULTATION SECTION: REFRACTIVE
RSB thickness safety limit is 300 mm. Female patients should be carefully selected for refractive surgery because should they become pregnant in the future, it could trigger post-LASIK corneal ectasia. The corneal refraction procedure that seems more suitable for the current refractive case is PRK. The high manifest refraction of the patient could contribute to intraoperative and postoperative complications (eg, myopic regression, corneal haze, overtreatment, and undertreatment). These are difficult to address in cases involving a very thin post-PRK cornea; the post-PRK residual stromal thickness should be at least 300 mm because if it were thinner, the options for retreatment would be limited. Alternatively, with this type of case I might take an intraocular treatment approach. Refractive lens exchange (using a toric IOL) could not be a solution for a myopic patient of this age because the risk for retinal detachment is high. Another possible solution is implantation of a pIOL in the posterior chamber, which has the advantage of maintaining accommodation. In the current case, the patient is not tolerating spectacles and the ACD measurements indicate that a posterior chamber pIOL (correcting myopia and astigmatism) could be implanted safely. However, the possibility of early cataract formation and the need for repeating surgery for pIOL extraction and cataract in the near future (in a 38-year-old patient) should be considered. In conclusion, in the current case I would prefer not to perform refractive surgery. The proper contact lens use seems the most preferable decision for this patient because of her age, the thin corneas, and the high attempted correction. If the patient remained highly motivated for refractive surgery, I would probably refer her to another refractive surgeon. George D. Kymionis, MD, PhD Heraklion, Crete, Greece
REFERENCES 1. Elsheikh A, Wang D, Brown M, Rama P, Campanelli M, Pye D. Assessment of corneal biomechanical properties and their variation with age. Curr Eye Res 2007; 32:11–19 JL, Vega-Estrada A, Baviera J, Beltra n J, Cobo2. Brenner LF, Alio Soriano R. Clinical grading of post-LASIK ectasia related to visual limitation and predictive factors for vision loss. J Cataract Refract Surg 2012; 38:1817–1826
- In my opinion, the best option in this case is implantation of a toric pIOL. The cornea is thin and has no existing or suspected keratoconus or other corneal ectasia, as supported by the topography, tomography, and OCT examinations. When the CCT is less than 500 mm, I
always perform PRK instead of LASIK, even when using a femtosecond laser to create a predictably thin flap. Moreover, I do not perform laser treatment if the CCT is less than 450 mm. To keep the post-LASIK risk low, I require an RSB of at least 300 mm (not 250 mm) and a total corneal thickness of at least 400 mm. I would not perform laser treatment in this case because the measurements are outside those requirements. For patients 21 to 50 years old, my inclination is to use pIOLs instead of RLE because of the increased risk for retinal damage or retinal detachment. For patients older than 50 years, I am inclined to replace the lens, and in some cases involving high myopia, monovision is a good alternative to multifocal IOLs. In this case, the ACD in the right eye is 3.38 mm and in the left eye is 3.41 mm. Both eyes are over the 3.0 mm requirement to implant safely an iris-fixated or posterior chamber pIOL. Another important condition for pIOL implantation is an endothelial cell count (ECC) of over 2000 cells/mm2; thus, an ECC should be performed before making the final decision in this case. Miguel Srur, MD Santiago, Chile EDITOR’S COMMENT This is an interesting, well-documented case that presents a thin cornea but normal results from other examinations performed using different technologies, including symmetric bow-tie pattern WTR Placido topography with normal regional relative thickness profiles obtained with tomography.1 Based on the data, some surgeons consider that this could be a normal thin cornea or a sign of pre-topographic ectatic disease. Many also consider that even if it is normal, a cornea this thin is very close to a higher risk level for the percentage of tissue altered, which has been shown to be a robust risk factor for post-LASIK ectasia.2–4 All respondents note that the risk factorsda potentially high percentage of tissue altered and a cornea more than 3 standard deviations thinner the normaldare enough to preclude LASIK, even with the more predictable flaps with modern microkeratomes and femtosecond lasers. Some respondents consider surface ablation a reasonable option, especially considering the patient's age. If the patient were younger than 30 years, even surface ablation might not be an option because this patient could still present some topographic signs of an ectatic disease.1 Other approaches discussed include small-incision lenticule extraction,5 which theoretically has less biomechanical impact, and a toric posterior
J CATARACT REFRACT SURG - VOL 41, JUNE 2015
