Lens-Induced Astigmatism Worsens Photopic Distance Vision

Lens-induced astigmatism is well-tolerated at near distances, but not for far distances in photopic conditions, according to a study published in Clinical Optometry. This may be due to a long-term neural adaptation in the visual pathway that creates a tendency for the eye to toward an inherent astigmatism at near viewing, the report suggests.

Investigators examined lens-induced astigmatism at multiple cylindrical powers (−0.25, −0.50, −0.75, −1.00, −1.50, and −2.00 diopters [D]) among individuals with myopia and presbyopia using both with-the-rule and against-the-rule axis orientations. The team performed assessments in photopic and mesopic conditions using both low contrast (LC) and high contrast (HC) stimuli and evaluated visual acuity changes with each condition.

Visual acuity in photopic conditions deteriorated significantly at far distance in both with-the-rule and against-the rule conditions compared with near (P =.0061 and P =.0017, respectively), the report shows. When no lens-induced astigmatism was introduced, best-corrected visual acuity was similar at near and far distances with HC stimuli in both photopic (mean -0.14 logarithm of the minimum angle of resolution [logMAR] for both; P =.824) and mesopic (0.09 vs 0.05 logMAR; P =.123) conditions. With LC stimuli, visual acuity differed significantly in photopic (P =.001) and mesopic (P =.027) conditions.

Myopia level did not significantly affect visual acuity deterioration, according to the report.

Visual acuity deterioration at near and far distances differed significantly with HC (mean slope, 0.15 vs 0.22 D^-1; P =.0061) and LC (mean slope, 0.13 vs 0.22 D^-1; P =.0001) stimuli in with-the-rule lens-induced astigmatism and with HC (mean slope, 0.12 vs 0.18 D^-1; P =.0017) and LC (mean slope, 0.10 vs 0.20 D^-1; P =.0001) against-the-rule lens-induced astigmatism, both in photopic conditions, respectively. Similarly, visual acuity deterioration depended on photopic and mesopic conditions at far distances with LC stimuli in lens-induced with-the-rule (mean slope, 0.22 vs 0.12 D^-1; P =.0006) and against-the-rule (mean slope, 0.20 vs 0.14 D^-1; P =.0023) scenarios, respectively.

“In photopic conditions with HC stimuli, the tolerance to astigmatism blur was found better at near than at far distance,” according to the study authors. “This is here tentatively attributed to a possible long-term experience-mediated neural compensation associated to the tendency of the eye toward an inherent astigmatism at near, similarly as found in the literature in case of spherical defocus blur for subjects with relatively high myopia.”

Study limitations include a small sample size and the inclusion of participants with natural astigmatism, which may have affected differences between with-the-rule and against-the-rule lens-induced astigmatism.

Disclosure: This research was supported by Hoya Vision Care. Please see the original reference for a full list of disclosures.