Evaluating the visual benefits of toric soft contact lenses using a novel pupil-controlled vision testing system

This study investigated the clinical astigmatism threshold at which toric soft contact lenses (CLs) provide superior visual acuity (VA) compared with spherical CLs, and how pupil size affects this. A novel pupil-controlled vision testing system (PUCS) was developed to assess VA across different pupil sizes by dynamically adjusting lighting conditions.

A randomised, crossover, partially participant-masked clinical study was conducted with 53 habitual soft CL wearers (84 eyes; ages 20-40). Eyes were categorised into seven astigmatism groups (0.00 to -1.50 DC in 0.25 DC steps). Each eye was tested with three corrections: spherical soft CLs, custom toric soft CLs, and full-correction spectacles. VA was assessed using PUCS at five pupil diameters (2.5 mm, 4.0 mm, 5.5 mm, maximum, and minimum). The primary outcome was the between-correction difference in PUCS logMAR visual acuity, assessed at each pupil diameter. Secondary measures included conventional VA, subjective ratings, and lens preference.

PUCS VA decreased significantly with increasing pupil diameter across all corrections (p< 0.0001). Toric CLs provided significantly better PUCS VA than spherical CLs for astigmatism of -0.75 DC and greater, regardless of pupil diameter (p< 0.001). The mean toric-spherical difference was approximately 0.06 logMAR (≈3 letters) at -0.75 DC and 0.12 logMAR (≈6 letters) at -1.50 DC. Toric CL performance was comparable to spectacle correction across all cylinder groups. Participants favoured toric CLs over spherical lenses from -0.75 DC upwards, with no participants preferring spherical CLs at -1.25 DC or greater (p< 0.001). Toric CLs demonstrated excellent rotational stability.

The PUCS system provided robust evidence that toric CLs offer significant visual benefits at -0.75 DC or greater (within the tested range up to -1.50 DC), irrespective of pupil diameter. These findings support routine soft toric CL prescribing for astigmatism correction at or above this threshold to optimise visual performance and patient satisfaction.

This study was registered at ClinicalTrials.gov (Identifier: NCT04613882).