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Study: More astigmatism produces no near vision benefit in distance-corrected eyes
No beneficial effects of increasing astigmatism were observed in a study investigating the influence of astigmatism on distance-corrected near visual acuity and reading performance.
In a consecutive case series evaluated by M. Casagrande and colleagues, 0 D, -0.75 D and -1.5 D of with-the-rule (WTR) and against-the-rule (ATR) astigmatism were simulated in 23 eyes of 23 participants. All subjects were cyclopleged and corrected for distance. Standardized sentences were used in the evaluation of reading acuity (RAc) and reading speed (RS). The Salzburg Reading Desk, which consists of a Snellen E chart on a thin film transistor display, was used to evaluate near visual acuity (NVA).
An increasing amount of astigmatism resulted in a decrease in NVA, particularly for -1.5 D subjects (P = .005), and a decrease in RAc (P = .002 for -0.75 D; P = .014 for -1.5 D).
WTR astigmatism reduced NVA and RAc and resulted in a lower RS compared with ATR astigmatism (P < .001). NVA was better than RAc when there was no astigmatism (P = .03), -0.75 D WTR (P = .001) and -1.5 D WTR (P = .03). No difference was seen in NVA and RAc for -0.75 D ATR and -1.5 D ATR.
The researchers concluded: “WTR astigmatism results in reduced reading parameters and NVA for -0.75 D and -1.5 D astigmatism compared with corresponding ATR astigmatism and no astigmatism added.”