
09/09/2025
“Reading in dim light causes permanent eye damage” — a pervasive clinical myth worth correcting.
Physiologically, low ambient luminance reduces retinal illuminance and contrast sensitivity, which increases accommodative and vergence effort during near tasks. Patients respond with increased squinting and altered eyelid posture, producing symptoms of asthenopia (ocular discomfort), transient blur and headache. These symptoms reflect functional, muscle-mediated fatigue and reduced visual performance under suboptimal lighting — not irreversible structural injury to ocular tissues.
Key points for clinicians and educators:
Mechanism: decreased luminance → lower retinal signal-to-noise ratio → greater accommodative/convergence demand and compensatory squinting → symptomatic asthenopia.
Clinical implication: symptomatic relief is achieved by optimizing task luminance/contrast, ensuring an up-to-date refractive correction, and addressing binocular vision anomalies or accommodative dysfunction where present.
Differential & assessment: when patients report persistent symptoms despite adequate lighting and refractive correction, evaluate for uncorrected refractive error, accommodative/vergence disorders (near point of accommodation/convergence, accommodative facility), contrast sensitivity deficits, dry eye, and neurologic causes as indicated.
Teaching tip: transform the myth into a short, evidence-based lab exercise — compare visual acuity/contrast sensitivity/accommodative facility under controlled luminance conditions and have students document symptom changes and management decisions.
While environmental lighting influences visual comfort and performance, current clinical evidence does not support the assertion that routine near work in dim illumination produces permanent structural damage to the eye