A 44-YEAR-OLD FEMALE presented wearing soft spherical contact lenses and reporting difficulty seeing at night, particularly while driving. The problem had become so severe that she was forced to leave her job as a bus driver, which required early-morning driving during dark hours. The patient’s distance visual acuity was 20/30 under dim illumination. When a light was shone at the nontested eye, her acuity improved to 20/20.
The Optical Impact of Pupil Size: Pupil size has long been recognized as a significant factor influencing visual quality. Larger pupils, particularly under mesopic or scotopic conditions, allow peripheral optical aberrations to have a greater impact on retinal image quality (Wang et al, 2013). A dilated pupil exposes a wider optical zone of the cornea and crystalline lens, where optical imperfections tend to increase, and this results in decreased contrast sensitivity and increased glare or halo effects (Fan-Paul et al, 2002; Glasser and Campbell, 1998).
Testing for Pupil-Dependent Vision Changes: The clinical case presented here describes a simple test to discover pupil-related vision issues. Testing acuity in low illumination while shining a light in the nontested eye helps determine whether pupil size is influencing vision (Figure 1). Improvement in vision when the pupil constricts suggests that peripheral optical aberrations are contributing to reduced vision. Wavefront aberrometry coupled with pupillometry allows objective evaluation of aberrations at different pupil sizes (Wang et al, 2013).
Leveraging Small Pupils in Presbyopia: Pupil constriction can also enhance depth of focus, improving functional vision in presbyopes. This optical principle underlies several modern pharmacologic approaches to presbyopia correction. Pilocarpine at 0.4% and 1.25% and aceclidine at 1.44% are currently approved for presbyopia treatment (Orman and Benozzi, 2023; Grzybowski and Ruamviboonsuk, 2022). Investigational miotics, including a carbachol/brimonidine combination and phentolamine, are currently being studied (Orman and Benozzi, 2023; Grzybowski and Ruamviboonsuk, 2022).
Clinical Implications: Simple tests allow practitioners to identify patients whose visual complaints stem from mesopic pupil dilation rather than refractive error alone. They can exploit this to modulate pupil size therapeutically to enhance night vision or near focus.
The Verdict
Brimonidine prevents pupil dilation in low light (Gerente et al, 2007; Tuncer et al, 2020). We gave the patient eye drops containing 0.025% brimonidine, to be utilized 15 minutes prior to placing her contact lenses on. This reduced pupil dilation in low-light conditions, improving her night vision.
Pupil size may influence visual performance in both presbyopic and nonpresbyopic patients. As pharmacologic and optical strategies for dynamic pupil management continue to evolve, they provide us with tailored interventions for patients who have poor night vision.
If large pupils are the new norm, we don’t want to be normal.
References
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3. Glasser A, Campbell MCW. Presbyopia and the optical changes in the human crystalline lens with age. Vision Res. 1998;38(2):209-229. doi: 10.1016/s0042-6989(97)00102-8
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7. Tuncer I, Bilgin S, Özgür Zengin M, et al. Effect of brimonidine tartrate 0.15% on scotopic pupil size and upper eyelid position: controlled trial. Eye (Lond). 2020;35(2):672-675. doi: 10.1038/s41433-020-1007-9
