Corneal Transplantation in Disease Affecting Only One Eye: Does It Make a Difference to Habitual Binocular Viewing?

Abstract

BackgroundClarity of the transplanted tissue and restoration of visual acuity are the two primary metrics for evaluating the success of corneal transplantation. Participation of the transplanted eye in habitual binocular viewing is seldom evaluated post-operatively. In unilateral corneal disease, the transplanted eye may remain functionally inactive during binocular viewing due to its suboptimal visual acuity and poor image quality, vis-à-vis the healthy fellow eye.Methods and FindingsThis study prospectively quantified the contribution of the transplanted eye towards habitual binocular viewing in 25 cases with unilateral transplants [40yrs (IQR: 32–42yrs) and 25 age-matched controls [30yrs (25–37yrs)]. Binocular functions including visual field extent, high-contrast logMAR acuity, suppression threshold and stereoacuity were assessed using standard psychophysical paradigms. Optical quality of all eyes was determined from wavefront aberrometry measurements.Binocular visual field expanded by a median 21% (IQR: 18–29%) compared to the monocular field of cases and controls (p = 0.63). Binocular logMAR acuity [0.0 (0.0–0.0)] almost always followed the fellow eye’s acuity [0.00 (0.00 –-0.02)] (r = 0.82), independent of the transplanted eye’s acuity [0.34 (0.2–0.5)] (r = 0.04). Suppression threshold and stereoacuity were poorer in cases [30.1% (13.5–44.3%); 620.8arc sec (370.3–988.2arc sec)] than in controls [79% (63.5–100%); 16.3arc sec (10.6–25.5arc sec)] (p<0.001). Higher-order wavefront aberrations of the transplanted eye [0.34μ (0.21–0.51μ)] were higher than the fellow eye [0.07μ (0.05–0.11μ)] (p<0.001) and their reduction with RGP contact lenses [0.09μ (0.08–0.12μ)] significantly improved the suppression threshold [65% (50–72%)] and stereoacuity [56.6arc sec (47.7–181.6arc sec)] (p<0.001).ConclusionsIn unilateral corneal disease, the transplanted eye does participate in gross binocular viewing but offers limited support to fine levels of binocularity. Improvement in the transplanted eye’s optics enhances its participation in binocular viewing. Current metrics of this treatment success can expand to include measures of binocularity to assess the functional benefit of the transplantation process in unilateral corneal disease.

A computational analysis of retinal image quality in eyes with keratoconus

“…The results of this study are in agreement with the previous literature on how increases in HOA's influence IQ in otherwise normal eyes 17,18,20,21 or in subjects who undergo LASER refractive surgery 16 or corneal transplants 29 . The latter two patient-based cohorts more closely resemble the present keratoconus cohort in that the increased HOA's and the associated reduction of IQ amplitude is rather long-standing and relatively more permanent than in normal eyes with induced HOA's.…”

“…It is therefore possible that these three patient cohorts may experience some form of neural recalibration to the altered retinal IQ that may enhance or negatively impact their visual performance 12,13 . Furthermore, unlike the refractive surgery and corneal transplant cohorts where the IQ deterioration may be relatively stable post-operatively 29,30 , the keratoconus cohort may experience a progressive deterioration of IQ with worsening of the disease. It would therefore be of interest for a future study to longitudinally track changes in IQ of eyes with progressing keratoconus and to compare them to changes in psychophysical visual performance.…”

Binocular cross-correlation analyses of the effects of high-order aberrations on the stereoacuity of eyes with keratoconus

“…Stereoacuity (i.e., the smallest disparity that stimulates stereo depth) and the upper disparity limit (i.e., the largest disparity that stimulates stereo depth) are correlated with the overall magnitude and interocular differences in HOAs. More specifically, stereoacuity is worse in subjects with keratoconus and with surgical interventions like penetrating keratoplasty for corneal transplantation and LASIK refractive surgery, where HOAs are increased and mismatched between eyes (Bandela, Satgunam, Garg, & Bharadwaj, 2016; Nilagiri, Metlapally, Kalaiselvan, Schor, & Bharadwaj, 2018). On the other hand, the upper disparity limit that goes beyond the limit of binocular fusion (Duwaer, 1983; Howard & Rogers, 2012) is lowered with increasing interocular differences of HOAs (Jimenez, Castro, Hita, & Anera, 2008).…”

“…On the other hand, the upper disparity limit that goes beyond the limit of binocular fusion (Duwaer, 1983; Howard & Rogers, 2012) is lowered with increasing interocular differences of HOAs (Jimenez, Castro, Hita, & Anera, 2008). Also, stereoacuity losses are partially recovered when subjects switch from sphero-cylindrical spectacles to rigid gas-permeable contact lenses (RGP CLs) that minimize HOAs (Bandela et al, 2016; Nilagiri et al, 2018).…”

A new technique for fitting of tricurve rigid gas-permeable contact lens in penetrating keratoplasty eyes using Scheimpflug imaging

“…reported that RGP contact lenses improve the suppression threshold and stereoacuity in patients who have undergone PK in one eye. [ 21 ] RGP contact lens use after PK is considered to be safe if an acceptable fitting is achieved. In addition, RGP contact lenses do not affect endothelial cell density in eyes with corneal transplants even if the lenses are worn on a daily basis.…”