Patel, Sanjay V.

AbstractUnraveling the genetic mechanisms of Fuchs endothelial corneal dystrophy has opened new possibilities for future targeted medical therapy of the disease. Until these possibilities mature, regenerative semi-surgical approaches by cell injection or cell sheet transfer could help expand the donor pool, and possibly enable autologous transplantation. Descemet membrane stripping alone and acellular Descemet membrane transfer are more immediate surgical approaches that could be temporary treatments in some patients, though there is a lack of understanding of the factors that predict success for these procedures. Regardless of approach, clinical trials will be necessary, and clinicians should therefore try to standardize their methods of assessing disease severity and the outcomes of intervention.

Purpose: Patients with Fuchs endothelial corneal dystrophy (FECD) often notice poor vision in the morning that improves as the day progresses. In this study, we determined changes in corneal optical properties associated with induced corneal edema. Methods: Twenty-three phakic eyes (23 participants) with FECD (grades 1–6, modified Krachmer scale) and 8 normal eyes (8 participants) were examined by Scheimpflug photography. Central corneal thickness, high-order aberrations from anterior and posterior corneal surfaces, and backscatter from the anterior, mid-, and posterior cornea were determined from the Scheimpflug images. A low-oxygen permeable contact lens was placed on the eye, and eyes were closed for 2 hours, after which the lens was removed and Scheimpflug photography was repeated for up to 5 hours to determine changes in backscatter and high-order aberrations. Results: Corneas swelled by 10% [95% confidence interval (CI), 9–10]. Backscatter from the anterior cornea increased by 416 scatter units (SU, 95% CI, 344–488; P < 0.001), independent of the presence and severity of FECD. Recovery of anterior backscatter was slower in advanced FECD (81 SU/h, 95% CI, 60–120) compared with normal (123 SU/h, 95% CI, 95–150; P = 0.019). Anterior and posterior corneal high-order aberrations, and mid and posterior backscatter, did not increase with induced swelling. Conclusions: Inducing corneal edema increases anterior corneal backscatter but not high-order aberrations. Subjective poor vision in the morning in FECD is probably caused by scattered light rather than by high-order aberrations, suggesting that these patients experience more disability glare than decreased visual acuity.

PurposeIn normal eyes, a fixed relationship between anterior and posterior corneal astigmatism is assumed, especially for lens power calculations. This study assessed the association between anterior and posterior corneal astigmatism and thickness.MethodsNormal corneas were examined by slit‐lamp microscopy and Scheimpflug imaging. The differences between vertical and horizontal thicknesses at 4‐mm and 6‐mm‐diameters were calculated. Anterior and posterior astigmatism were calculated as the difference between steep and flat powers based on the corresponding radii of curvature and refractive indices. Comparisons and significances of correlations were assessed by using generalized estimating equation models.ResultsFifty‐four subjects (101 corneas) aged 18–80 years were included. Peripheral corneas were thicker vertically than horizontally (p < 0.001) at 4 mm by 13.4 ± 9.4 µm (mean ± standard deviation) and at 6 mm by 8.6 ± 4.8 µm. Anterior corneal astigmatism was 1.08 ± 0.57 D and was aligned vertically (73%), horizontally (6%), or obliquely (21%). Posterior corneal astigmatism was −0.31 ± 0.13 D and was aligned vertically (94%) or obliquely (6%). Anterior and posterior astigmatism were correlated in eyes with vertical anterior astigmatism (r = 0.65; p < 0.001), but not in eyes with oblique or horizontal anterior astigmatism. The difference between vertical and horizontal corneal thickness correlated with posterior astigmatism at 4 mm (r = −0.58; p < 0.001) and at 6 mm (r = −0.61; p < 0.001).ConclusionsThe posterior cornea is normally ellipsoid in shape with a steep vertical meridian that corresponds to the cornea being thicker in the vertical paracentral region. Understanding the normal relationship between anterior and posterior corneal surfaces is important when assessing the same in corneal diseases.