Impact of the Reference Point for Epithelial Thickness Measurements

Therapeutic visual rehabilitation in a patient with high hyperopia and flat cornea years after radial keratotomy

A 51-year-old man was referred for refractive surgery evaluation. Spectacle dependence and poor visual quality in both eyes was his chief complaint. He cannot tolerate contact lenses. Corrected distance visual acuity (CDVA) was 20/40 in both eyes. Manifest refraction was +5.25 -2.25 @ 90 (20/40) in the right eye and +6.25 -2.25 @ 105 (20/40) in the left eye. The patient had a history of radial keratotomy (RK) almost 30 years ago in both eyes and at the slitlamp presented 8 RK incisions, proportionally spaced between one another. All incisions were closed, and there were no relevant signs of scarring. The patient denied any history of ocular trauma, systemic disease, or medications. Corneal topography with different technologies revealed an irregular pattern with marked central flattening in both eyes, with some points below 30 diopters (D) (Supplemental Figures 1 and 2, available at http://links.lww.com/JRS/A862 and http://links.lww.com/JRS/A863, respectively). There were no signs of cataract, and fundus examination was normal. Optical coherence tomography (OCT) of the right eye revealed a more homogeneous thickness pattern, little variation between the thinnest and thickest areas, and adequate transparency (Figure 1JOURNAL/jcrs/04.03/02158034-202306000-00018/figure1/v/2023-05-31T172126Z/r/image-tiff). In the left eye, there is wide variability between the thinnest and thickest stromal points, with annular thinning and central thickening (Figure 2JOURNAL/jcrs/04.03/02158034-202306000-00018/figure2/v/2023-05-31T172126Z/r/image-tiff). Both eyes show marked epithelial irregularity. Considering this patient's current ocular status, how would you reach visual rehabilitation? Because he is contact lens intolerant, would you consider surface ablation, for example, photorefractive keratectomy (PRK) with mitomycin-C (MMC)? If that were the case, would you think of an optimized or a topography-guided (TG) treatment? Would you immediately consider a corneal transplant option? Would you instead consider a more conservative approach? Which one and why?

Early Corneal and Epithelial Remodeling Differences Identified by OCT Imaging and Artificial Intelligence Between Two Transepithelial PRK Platforms

PURPOSE

To analyze corneal and epithelial remodeling differences between SmartSurfACE reverse transepithelial PRK (SCHWIND eye-tech-solutions) and Streamlight (Alcon Laboratories, Inc) transepithelial PRK procedure using optical coherence tomography (OCT) and artificial intelligence (AI).

METHODS

This was a prospective, interventional, and longitudinal study. A contralateral eye study was conducted in which one eye was assigned to the SmartSurfACE group and the fellow eye was assigned to the Streamlight group. OCT was performed preoperatively and 1, 3, and 6 months after surgery. Uncorrected (UDVA) and corrected (CDVA) distance visual acuity and residual refractive error was measured only preoperatively and at 3 and 6 months. From OCT, curvature and aberrations of the air-epithelium (A-E) interface, epithelium-Bowman's layer (E-B) interface, and epithelium Zernike indices (EZI) were derived. Pain was evaluated at 1 day postoperatively using the Wong-Baker scale.

RESULTS

Both groups had similar UDVA, CDVA, residual refractive error, and changes in A-E and E-B curvatures at 3 and 6 months postoperatively (P > .05). However, many parameters indicated that the Streamlight group underwent a greater change in A-E aberrations, E-B aberrations, and EZI than the SmartSurfACE group postoperatively (P < .05). The EZI indicated a greater level of epithelial thickness distortion in the Streamlight group than in the SmartSurfACE group (P < .05). Using AI, the EZI were most indicative of remodeling differences between the two groups. Further, the pain was significantly greater at 1 day in the Streamlight group (P < .05).

CONCLUSIONS

Early remodeling differences existed because the Streamlight procedure removed a greater amount of epithelium than the SmartSurfACE procedure. However, the visual and refractive outcomes were comparable. [J Refract Surg. 2020;36(10):678-686.].

Thermal Load During Corneal Excimer Laser Ablation: Impact of Different Ablation Parameters

PURPOSE

To characterize the impact of different ablation parameters on the change in peak corneal temperature during corneal excimer laser ablation.

METHODS

Forty-two ablations were performed (21 on polymethylmethacrylate [PMMA] and 21 on porcine eyes) simulating photorefractive keratectomy (PRK), transepithelial PRK, and laser in situ keratomileusis (LASIK) treatments. Each ablation was recorded using infrared thermography. The change in peak corneal temperature was analyzed with respect to varying ablation parameters.

RESULTS

Excellent correlation between the temperature rise in PMMA and porcine eyes was found. The change in peak corneal temperature was significantly higher in myopic than in hyperopic corrections, ranging from 6 °C for hyperopic corrections to 16 °C for a -18.00 diopters (D) correction. The change decreased with larger optical zones. Of all analyzed metrics, the refractive correction together with the maximum slope of the treatment showed the best coefficient of determination. Transepithelial ablations led to a higher change in peak corneal temperature than pure stromal ablations. Isothermal lines as a function of the refractive correction and optical zone diameter were calculated with a hypersurface model. If keeping the change in peak corneal temperature below 8 °C is the limit, only 3.00 to 4.00 D can be treated (6.5 mm or larger optical zone); for 10 °C, a maximum of 7.00 D (7 mm or larger optical zone) can be treated and for 12 °C, 10.00 D can be treated (6 mm or larger optical zone).

CONCLUSIONS

The effect of different parameters on change in peak corneal temperature during corneal laser ablation could be quantitatively evaluated. Cooling the cornea may aid in avoiding thermal denaturation. This is particularly important for transepithelial ablations, which further increase the thermal load due to the extra ablation of the epithelium. [J Refract Surg. 2020;36(10):667-676.].