The influence on unaided vision of age, pupil diameter and sphero‐cylindrical refractive error

Abstract

Background

The aim was to derive equations for the relationship between unaided vision and age, pupil diameter, iris colour and sphero‐cylindrical refractive error.

Methods

Data were collected from 663 healthy right eyes of white subjects aged 20 to 70-years. Subjective sphero‐cylindrical refractive errors ranged from ‐6.8 to +9.4 D (mean spherical equivalent), ‐1.5 to +1.9 D (orthogonal component, J₀) and ‐0.8 to 1.0 D (oblique component, J₄₅). Cylinder axis orientation was orthogonal in 46 per cent of the eyes and oblique in 18 per cent. Unaided vision (‐0.3 to +1.3 logMAR), pupil diameter (2.3 to 7.5-mm) and iris colour (67 per cent light/blue irides) was recorded. The sample included mostly females (60 per cent) and many contact lens wearers (42 per cent) and so the influences of these parameters were also investigated.

Results

Decision tree analysis showed that sex, iris colour, contact lens wear and cylinder axis orientation did not influence the relationship between unaided vision and refractive error. New equations for the dependence of the minimum angle of resolution on age and pupil diameter arose from step backwards multiple linear regressions carried out separately on the myopes (2.91.scalar vector +0.51.pupil diameter ‐3.14 ) and hyperopes (1.55.scalar vector + 0.06.age – 3.45 ).

Conclusion

The new equations may be useful in simulators designed for teaching purposes as they accounted for 81 per cent (for myopes) and 53 per cent (for hyperopes) of the variance in measured data. In comparison, previously published equations accounted for not more than 76 per cent (for myopes) and 24 per cent (for hyperopes) of the variance depending on whether they included pupil size. The new equations are, as far as is known to the authors, the first to include age. The age‐related decline in accommodation is reflected in the equation for hyperopes.

Key words:

• age
• ametropia
• pupil
• vision

Acknowledgements

The authors wish to acknowledge all of the staff at Specsavers in Salisbury, who assisted in data collection. They also wish to thank the reviewers of the original manuscript, whose suggestions greatly improved its clarity.