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StudyBMJ open ophthalmology · 2026

Visual acuity degradation under positive lens-induced myopic defocus at nominal chart contrast levels in young adults: a repeated-measures study.

Shivani Sah, Suraj Chettri, Pragati Gautam, Gauri Shankar Shrestha

OphthalmologyStudy

Optical blur from positive lenses significantly worsens visual acuity

Visual acuity degradation under positive lens-induced myopic defocus at nominal chart contrast levels in young adults: a repeated-measures study.

Shivani Sah … Gauri Shankar Shrestha

BMJ open ophthalmology · 2026

Purpose

To quantify visual acuity (visual acuity) degradation across nominal chart contrast levels under graded positive lens-induced myopic defocus and to determine whether corrected low myopes differ from emmetropes in their acute response to optical blur.

Methods

In this repeated-measures study, 300 adults aged 18-35 years (150 low myopes and 150 emmetropes) underwent monocular logMAR visual acuity assessment at 6 m.

n = 300 adults

Results

partial η²=0.471

blur from the added lenses strongly reduced how clearly people could see

n = 300 adults

More results

Progressively lower nominal chart contrast levels also significantly worsened visual acuity (p<0.001, partial η²=0.237).

A small but significant Defocus×Contrast interaction was observed (p<0.001, partial η²=0.015), indicating slightly greater blur-related degradation at lower nominal contrasts.

More results

No clinically meaningful interactions involving refractive group were observed.

Although myopes demonstrated slightly poorer overall visual acuity than emmetropes (mean difference 0.041 logMAR; p<0.001, partial η²=0.056), refractive status had little influence on the overall pattern of acuity decline across defocus or contrast levels.

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Conclusion · 1 of 2

Visual acuity degradation under positive lens-induced myopic defocus is primarily determined by the magnitude of optical blur, with reduced contrast exerting an additional but smaller effect.

Conclusion · 2 of 2

Corrected low myopes and emmetropes show broadly comparable functional responses to acute defocus under natural viewing conditions, although subtle subgroup differences cannot be excluded.

Post

Visual acuity degradation under positive lens-induced myopic defocus at nominal chart contrast levels in young adults: a repeated-measures study.

Optical blur from positive lenses significantly worsens visual acuity

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