Eyeworld

46 | EYEWORLD | FALL 2024 R EFRACTIVE References 1. Prospero Ponce CM, et al. Central and peripheral corneal thickness measured with optical coherence tomography, Scheimpflug imaging, and ultrasound pachymetry in nor- mal, keratoconus-suspect, and post-laser in situ keratomileusis eyes. J Cataract Refract Surg. 2009;35:1055–1062. 2. Rocha KM, Krueger RR. Spec- tral-domain optical coherence tomography epithelial and flap thickness mapping in femto- second laser-assisted in situ keratomileusis. Am J Ophthal- mol. 2014;158:293–301. 3. Reinstein DZ, et al. High-fre- quency ultrasound measure- ment of the thickness of the corneal epithelium. Refract Corneal Surg. 1993;9:385–387. 4. Reinstein DZ, et al. Arc-scan- ning very high-frequency digital ultrasound for 3D pachymetric mapping of the corneal epithe- lium and stroma in laser in situ keratomileusis. J Refract Surg. 2000;16:414–430. 5. Reinstein DZ, et al. Epithelial thickness in the normal cornea: three-dimensional display with Artemis very high-frequency digital ultrasound. J Refract Surg. 2008;24:571–581. 6. Reinstein DZ, et al. Corneal pachymetric topography. Oph- thalmology. 1994;101:432–438. 7. Reinstein DZ, et al. Corneal epithelial thickness profile in the diagnosis of keratoconus. J Refract Surg. 2009;25:604–610. 8. Reinstein DZ, et al. Epithe- lial and corneal thickness measurements by high-fre- quency ultrasound digital signal processing. Ophthalmology. 1994;101:140–146. 9. Reinstein DZ, et al. Com- parison of corneal epithelial thickness measurement between Fourier-domain OCT and very high-frequency digital ultrasound. J Refract Surg. 2015;31:438–445. 10. Reinstein DZ, et al. Epithelial, stromal, and total corne- al thickness in keratoconus: three-dimensional display with Artemis very-high frequency digital ultrasound. J Refract Surg. 2010;26:259–271. distribution. There can be more exaggerated thinning superiorly due to the friction from the eyelid, and that can introduce coma, aberration, and apparent astigmatism. If that's the case, you can increase lubrication and allow time for the corneal epithelium to recover before doing any procedure to correct the astigmatism. In the case of residual refractive error following cataract surgery, Dr. Reinstein said it's important to identify whether the visual com- plaints from the patient are actually the result of residual refractive error or due to the poor contrast and/or dysphotopsia associated with trifocal or multifocal IOLs. "Our plan of action would be to identify the root cause of the visual complaint," he said. "In addition to the refrac- tion and ocular examination, we use a range of diagnostic tests measuring the epithelium, topography/tomography, and visual quality measurements such as ocular scatter index, contrast sensitivity, light disturbance analyzer, Osiris aberrometer [CSO], subjective and objec- tive point spread function, C-Quant [Oculus], and QoV questionnaire." Provided that the patient has good quality of vision following the premium implant and if the cornea appears normal, Dr. Reinstein said LASIK would be the first-choice method to treat the residual refractive error in the majority of cases. "When screening for refractive surgery, every patient will undergo full topography and tomography including epithelial thickness mapping," he said. "If indicated, the patient will also have an ultrasound measurement of the epithelium using Insight 100 very high frequen- cy digital ultrasound [ArcScan]. In cases where the patient has undergone lens surgery with a premium implant, using a repeatable and accu- rate refraction technique is key. It is important that the refraction is also repeated on a separate date to ensure consistency of the results." Dr. Reinstein stressed that it is important that refractive surgeons understand the im- portance of preoperative epithelial thickness and the changes that can occur after myopic or hyperopic refractive surgery. "In my opinion, surgeons should not be performing refractive surgery without accurate and repeatable epithe- lial mapping," he said. "Most of the newer OCT devices have epithelial mapping function, which has made epithelial mapping more accessible. In our clinic all patients have their epitheli- um measured as standard at every preop and postop appointment." He added that epithelial mapping is important following intraocular sur- gery, as epithelial sloughing during surgery can cause irregularities in the epithelial surface that manifest as increased refractive astigmatism. He also noted the other applications of epithelial mapping, which include keratoconus screening, continued from page 44 Two distinct categories of epithelial irregularities—primary epithelial deformation and secondary epithelial modulation—can be distinguished by comparing OCT epithelial thickness maps with OCT topography maps. Source: David Huang, MD, PhD, and Yan Li, PhD

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