Abstract
Purpose :
Rigid contact lenses are the method of choice to optically correct advanced keratoconus. Such lenses may translate and rotate on-eye, changing the resulting Wavefront Error (WFE). This work assesses how this motion affects acuity in normal and keratoconic eyes.
Methods :
Previous SyntEyes models were expanded by adding the ability to shift and rotate a sphero-cylindrical rigid contact lens correction with respect to the center of a 5 mm pupil. More specifically, a simulated through-focus experiment of 20 normal and 20 keratoconic SyntEyes first objectively determined the centered sphero-cylindrical correction which optimized the visual Strehl (VSX). The optimal correction was then allowed to misalign ±1 mm in 0.1 mm steps and rotate ±15° in 1° steps, defining an ‘alignment space’. This provided 52 111 resultant WFE for each eye, which were used to calculate VSX, changes in which may be used to predict changes in logMAR acuity.
Results :
Keratoconic SyntEyes were significantly less tolerant to lens rotation than normal SyntEyes before potentially noticeable changes of more than 2 logMAR letters occur (t-test, p < 0.01), which varied considerably between individual eyes. These variations were not correlated with the amount of uncorrected astigmatism (p > 0.05) as the contact lenses dampened the corneal astigmatism. Normal SyntEyes had a significantly larger average tolerance to rotation than keratoconic cases (respectively, -14.1° to +13.4° and -10.5° to 10.6°; p < 0.01). Similarly, normal SyntEyes were also significantly more tolerant to decentration than keratoconus (0.39 ± 0.15 mm and 0.27 ± 0.13 mm, respectively).
Perfect alignment did not always provide the best possible optical correction, as in 9/20 keratoconic SyntEyes a gain of 1 or more letters was seen for a shifted or decentered lens position (Figure 1). This was also seen in 2/20 normal SyntEyes.
Conclusions :
Keratoconic eyes are more sensitive to smaller amounts of misalignment than normal eyes. In many cases, the best possible visual image quality may be obtained with a certain combination of decentration and rotation, rather than with perfect alignment.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.