LAG and LEAD of adaptation and their clinical significance

Accommodative lag refers to a reduced accommodative response relative to the required visual stimulus and is considered a normal finding during near vision, contributing to visual comfort. Lag values of up to +0.75 D at near viewing distances (33–40 cm) are generally regarded as within normal limits, whereas higher values are often associated with accommodative and/or vergence dysfunctions, inaccurate refractive correction, and symptoms of visual fatigue. Accommodative lag is influenced by age, cognitive load, and increased near visual demands, with higher values typically observed during demanding near tasks and in older individuals, particularly with the onset of presbyopia. Measurement of accommodative lag is primarily performed using objective dynamic retinoscopy techniques.

Monocular Estimated Method (MEM) retinoscopy is conducted at a fixed working distance with the brief introduction of spherical lenses until neutrality is achieved and is the most widely used technique in clinical practice. Nott retinoscopy relies on moving the retinoscope rather than introducing lenses and is considered less disruptive to the natural accommodative response. The Cross technique involves binocular insertion of spherical lenses to achieve neutrality, while open-field autorefractors provide an objective and reliable assessment of accommodative response by allowing natural viewing of the target. Although these techniques may yield slightly different values, the literature demonstrates good agreement among them, supporting their clinical usefulness in the evaluation of accommodation