Visual Interaction of Zernike Aberration Terms from 2nd to 5th Radial Orders with Vertical Coma

Purpose: Eyes with keratoconus suffer from an increased level of higher-order aberrations and decreased visual performance, even when corrected by conventional rigid contact lenses. This study aimed to characterize the visual interactions between the dominant residual aberration seen in this population (positive vertical coma: C7) and 2nd to 5th radial order Zernike aberration terms. Methods: The experiment proceeded in two parts. In part 1, individual Zernike aberration terms from the 2nd to 5th radial orders were combined in 0.05 μm steps from -2.00 to +2.00 μm with +1.00 μm of C7. The resulting combinations were used to calculate the visual Strehl ratio (VSX), which was used as a surrogate for the relative beneficial/deleterious impact of the combined condition, compared to C7 alone. For conditions where an interaction was predicted to provide the largest improvement (C6 and C17), high-contrast logMAR acuity charts were constructed to simulate the manner in which the combined condition defines the retinal image of the blurred chart. These charts were then read by three well-corrected, typically-sighted individuals through a 3.0-mm artificial pupil. In part 2, the interactions that were predicted to have a deleterious (rather than beneficial) visual interaction with C7 were characterized in greater detail. Results: In part 1, all aberration-containing conditions led to a reduction in visual image quality compared to the aberration-free condition. Levels of C6, C10, C15, C16, and C17 were identified that resulted in higher visual image quality than was observed with +1.00 μm of C7 alone. The acuities of subjects reading convolved charts had a strong correlation with the predicted performance from simulation (C6: r2 = 0.80, and C17: r2 = 0.76). In part 2, all combinations with C4, C5, C11, C12, C13, C18, and C19 were predicted to have worse logVSX than C7 alone. Conclusion: While most interactions reduced visual image quality, limited combinations provided a clinically relevant beneficial effect in the presence of C7. Future work will examine whether these effects persist as the aberration structure of the eye is made increasingly complex, up to the point it mimics an individual with keratoconus.