PUPIL SIZE IS in the news. The importance of pupil size is often included in discussions about myopia control, multifocal contact lens fitting, cataract and refractive surgery outcomes, and much more.

The pupil is a pretty amazing aperture. This remarkable gateway receives both parasympathetic and sympathetic innervation, regulates retinal illumination, and affects depth of focus and optical aberrations (Zele and Gamlin, 2020). The pupil dilates with increased attention and constricts with fatigue (Zele and Gamlin, 2020). The pupil is both complex and significant for optimal vision.

JUST AN AVERAGE PUPIL

Measuring pupil diameter is straightforward enough, but there are some important clinical considerations. Among the most important influences on pupil size is the luminance level (Guillon et al, 2016). Other factors affecting pupil size include the presence of accommodation, refractive error, and patient age (Guillon et al, 2016).

So, what is an average pupil size? Researchers have reported that when high, medium, and low luminance levels were averaged, the mean pupil size among all refractive errors was 4.21mm (ages 18 to 39 years), 3.84mm (ages 40 to 54 years), and 3.58mm (age 55-plus years) (Guillon et al, 2016).

PUPIL SIZE AND ASTIGMATISM?

Should clinicians consider pupil size when prescribing for astigmatism? In one study, uncorrected visual acuity was significantly worse in eyes with larger pupils (5mm) versus smaller pupils (2mm or 3mm) when against-the-rule or with-the-rule astigmatism was present (Kamiya et al, 2012).

In eyes with astigmatism, smaller pupil size has demonstrated an overall beneficial effect on distance and near visual acuity (Singh et al, 2013). Smaller pupil size is also beneficial to increasing depth of focus and decreasing higher-order aberrations and light scatter. A smaller pupil may also decrease the impact of astigmatic blur (Kamiya, 2012).

Factoring in pupil size may be helpful in determining a patient’s unique and optimal astigmatic correction (Figure 1). Pupil size continues to play a leading role when prescribing the best possible vision correction for patients. CLS

References

1. Zele AJ, Gamlin PD. Editorial: The Pupil: Behavior, Anatomy, Physiology and Clinical Biomarkers. Front Neurol. 2020 April Apr;11:1-5.
2. Guillon M, Dumbleton K, Theodoratos P, Gobbe M, Wooley CB, Moody K. The Effects of Age, Refractive Status, and Luminance on Pupil Size. Optom Vis Sci. 2016 Sep;93:1093-1100.
3. Kamiya K, Kobashi H, Shimizu K, Kawamorita T, Uozato H. Effect of pupil size on uncorrected visual acuity in astigmatic eyes. Br J Ophthalmol. 2012 Feb;96:267-270.
4. Singh A, Pesala V, Garg P, Bharadwaj SR. Relation between uncorrected astigmatism and visual acuity in pseudophakia. Optom Vis Sci. 2013 Apr;90:378-384.