The change of corneal shape in keratoconus subjects can impact the optical quality of the eye on the retina and it reduces the contrast sensitivity by light scattering. The aim of our study was to estimate the keratoconus subjects’ contrast sensitivity and visual acuity depending on keratoconus apex position. We included 45 keratoconus subjects (77 eyes), which have keratoconus in the first to the third stage, in our study. There were 33 eyes with keratoconus apex in the central part of the cornea and 46 eyes with keratoconus apex in the periphery of the cornea. Contrast sensitivity and visual acuity were measured at 3 m with and without the best possible spectacle correction using the FrACT program 3.9.3. The contrast sensitivity was measured at following frequencies – 1, 3, 5, 7, 9, 11, 13, and 15 cpd. The results showed that keratoconus subjects have lower contrast sensitivity in all spatial frequencies than subjects without pathological changes. The lowest contrast sensitivity was in keratoconus subjects with a central apex position compared to contrast sensitivity with peripheral apex position. The difference of contrast sensitivity between subjects with and without pathology increased up to 11 cpd but remained rather constant at the highest spatial frequencies – 11, 13, and 15 cpd. There was statistically significant difference between the median of visual acuity in subjects with central apex (0.42 decimal system) and subjects with peripheral apex (0.60 decimal system).
Contrast sensitivity decreases in keratoconus subjects even before the decrease is presented at high contrast visual acuity. The aim of our study was to estimate the subject’s contrast sensitivity and visual acuity in different keratoconus stages. In our study, there were included 45 keratoconus subjects (77 eyes) with the first, second and third keratoconus stages. Visual acuity and contrast sensitivity were measured at 3 m with the best possible spectacle correction and without vision correction using FrACT program 3.9.3. In the study, contrast sensitivity was measured at following spatial frequencies – 1, 3, 5, 7, 9, 11, 13 and 15 cpd. Contrast sensitivity analyse showed that there was a statistically significant difference among the contrast sensitivity of the first, second and third keratoconus stages in all spatial frequencies. If the keratoconus stage increased, the contrast sensitivity decreased more. The median visual acuity of first stage keratoconus subjects with spectacle correction was 0.56 (0.36, 0.65) decimal units, second stage keratoconus – 0.38 (0.21; 0.47) and third stage – 0.13 (0.08, 0.22).
The aberrations demonstrate the changes in light direction when it passes through the eye’s optical system. Our study goal was to evaluate the impact of keratoconus apex’s localization on eye aberration. 79 eyes were analysed in our study by keratoconus stage and by apex localization. Vertical coma had a statistically significant difference p=0.03 (Mann-Whitney test) between first (1.4 μm) and third (3.9 μm) keratoconus stage. The mean spherical aberration in case of central apex was 0.6 μm and in case of peripheral apex was 1.0 μm (p=0.01). The keratoconic eyes have increased corneal aberrations comparing to normal eyes.