The Effect of Age and Refractive Error on Pupil Size

Purpose: The size of the pupil plays a critical part in controlling the performance of all vision correction modalities incorporating a presbyopic correction, including contact lenses, refractive surgery and intraocular lenses. While the effect of luminance, the dominant factor affecting pupil size, is well known, little information is available regarding other contributing factors such as aging and refractive status. Methods: Three hundred and four patients (127 Male, 177 Female) aged 18 to 78 year made up the cohort population in this study. The non-interventional investigation involved a single visit to the OTG-i clinic. The pupil size was measured at three controlled luminance levels 250cd/m2 (daytime), 50cd/m2 (indoor lighting) and 2.5cd/m2 (night driving). Results: The results obtained showed that: (i) Pupil size decreases with age, the effect being most marked at low luminance. At 250cd/m2 means: 18-39 yrs = 2.8mm, 40-54 yrs = 2.67mm, 55+yrs = 2.56mm (p=0.046). At 50cd/m2 means: 18-39 yrs = 3.68mm, 40-54 yrs = 3.37mm, 55+yrs = 3.21mm (p<0.001). At 2.5cd/m2 means: 18-39 yrs = 6.15mm, 40-54yrs = 5.49mm, 55+yrs = 4.99mm (p<0.001). (ii) Pupil size at low luminance is significantly greater for myopes (high myopes mean = 5.98mm; low myopes mean = 5.91mm) than hyperopes (mean = 5.15mm) (p =0.020). (iii) Pupil size changes modelled by multi linear regression (p<0.001) identified age (p<0.001) and refractive error (p=0.019) as significant factors at low luminance. Conclusions: The study demonstrates that both age and refractive status affect pupil size with larger pupils measured for younger patients and myopes. The implications for the design of multifocal corrections are that the design should take into consideration both the age (faster progression for higher near additions) and refractive power (faster progression for hyperopic corrections).