Visual Acuity and Contrast Sensitivity Depending from Keratoconus Apex Position

Various studies have demonstrated that patients with keratoconus have significant loss of contrast sensitivity while its value varies in different studies. None of these studies has analysed reduced contrast sensitivity depending on the position of apex of corneal conus. Visual acuity and contrast sensitivity were evaluated for patients with keratoconus using the FrACT software. Contrast sensitivity was assessed at the following frequencies: 1, 3, 5, 7, 9, 11, 13, and 15 cycles per degree (cpd). Twenty-four eyes with keratoconus were analysed. Contrast sensitivity was significantly lower for patients with the apex at the centre compared with apex on the periphery both with (p = 0.0078) and without (p = 0.0078) spectacle correction. For patients with the apex at the centre, contrast sensitivity was significantly different with and without correction (0.02); however, there was no difference for patients with apex on the periphery (p = 0.06). The results showed that if the keratoconus apex is at the centre, then spectacle correction improves contrast sensitivity at lower spatial frequencies (1, 3, and 5 cpd), while it remains unchanged at medium and high spatial frequencies. If the keratoconus apex is on the periphery, spectacle correction does not improve contrast sensitivity.