Accuracy and repeatability of autorefraction in young adults: a comparison of cycloplegic and non-cycloplegic methods

Clinical Relevance: Cycloplegic refraction remains crucial in young adults, where accommodative activity can obscure accurate refractive status. Autorefractor repeatability is essential for precise optical correction and refractive error categorisation in clinical and research settings. Background: Cycloplegic autorefraction is recommended for individuals up to 20 years to prevent hyperopia underestimation and myopia overestimation. This study evaluated differences between non-cycloplegic and cycloplegic spherical equivalent refraction following cyclopentolate hydrochloride (cycloplegic agent) administration in young adults. This study also explored whether this difference varied by refractive status (hyperopia (≥1.00D), emmetropia (>−0.50, <1.00D), myopia (≤-0.50D)) or pre-instillation of proxymetacaine hydrochloride and whether cycloplegia improved autorefractor repeatability. Methods: Participants were 182 young adults (17–30 years) (mean (standard deviation): 21.66 (2.86) years). The right eye received 0.5% proxymetacaine hydrochloride and one (blue/green irides) or two drops (brown/hazel irides) of 1.0% cyclopentolate hydrochloride. The left eye received cyclopentolate hydrochloride only. Autorefraction was performed before and after cycloplegia. Analysis included paired t-testing, Deming regression, Bland-Altman analysis and equivalence testing. Results: Cycloplegic autorefraction was significantly more hyperopic than non-cycloplegic autorefraction (mean difference: 0.68(0.71) D in right eyes, 0.53(0.53) D in left eyes; p < 0.001) with 48.4% of participants exhibiting clinically significant differences of ≥ 0.50D. Agreement between non-cycloplegic and cycloplegic measurements was poor (limits of agreement: −0.71 D to +2.07 D, right eye). Hyperopes showed the greatest shift (1.39(0.91) D), compared to emmetropes (0.66(0.47) D) and myopes (0.31 (0.34) D). Cycloplegia improved repeatability, narrowing limits of agreement (−0.16 D to +0.15 D vs −0.24 D to +0.21 D). Proxymetacaine hydrochloride pre-instillation enhanced cycloplegic effect (+0.15 (0.07) D), particularly in hyperopic participants. Conclusions: A clinically significant difference was observed between non-cycloplegic and cycloplegic autorefraction in young adult participants, particularly among hyperopes. Cycloplegic measurements showed better repeatability, supporting their use for accurate refraction. Further research is needed on potential enhancing effects of proxymetacaine hydrochloride, particularly in diverse populations.