Article

PRESCRIBING FOR PRESBYOPIA

PUPIL MEASUREMENT: HITTING A MOVING TARGET

The impact of pupil size and dynamics on multifocal contact lens wear has often been a topic in this column. Whether for center-near or center-distance soft multifocal lenses, GP multifocal or bifocal lenses, or hybrid and scleral multifocal lenses, the size, dynamics, and position of the pupil and the accompanying line of sight are ultimately responsible for patient success.

There are several rules of thumb regarding pupil size. One is related to age; the older you are, the smaller your pupil becomes. Another is related to spectacle Rx; myopes tend to have larger pupils, while hyperopes’ are generally smaller. The lighting environment also plays a significant role; pupil size can change dramatically under scotopic versus photopic conditions. Finally, patients’ habitual environments, including lighting and working distance, can affect patient acceptance.

Determining Pupil Size

How pupils are measured in-office can be a variable, both within one examination lane or across multiple exam rooms. For instance, how often are illumination levels verified in your office?

Measuring illumination at the point of pupil documentation is also critical. At our Vision Research Institute in the Michigan College of Optometry, we recently tried a more novel approach to document pupil size with optical coherence tomography (Figure 1). We captured images at three different illuminations (0 lux, 238 lux ± 4 lux, and 605 lux ± 3 lux), then measured pupil size in this 62-year-old female using the instrument’s built-in calipers. Testing was done at 15-minute intervals, with the subject leaving the examination room, then returning just before testing to mimic light changes typically introduced in everyday practice. The pupil sizes were 3.44mm, 2.99mm and 2.74mm, respectively. While these differences may appear to be minimal, they are significant when compared to, for example, a 2.0mm bifocal optic zone.

Figure 1. Optical coherence tomography images comparing pupil size in the same patient under three different testing illuminations: A) 0 lux = 3.44mm, B) 238 lux = 2.99mm, C) 605 lux = 2.74mm.

Cardona and López (2016) attempted to determine working distance, pupil diameter, and illumination in real-life conditions in presbyopic patients performing different tasks. An investigator visited each study subject at work and home, making various measurements while they were performing their habitual tasks.

The goal was to increase practitioner awareness of the need to assess ocular parameters in conditions that are as similar as possible to those encountered by individual patients while performing their daily activities.

Respect Pupil Dynamics

Hopefully, someone will soon develop a mobile device app that can take all of the pertinent pupil measurements in a patient’s home and working environment, providing the most accurate information of all.

Recently, one of the major manufacturers made an effort to address pupil issues by offering an aspheric center-near design with optimized optics that addresses the variations in pupil size according to age and refractive power. The available parameters include 61 distance powers and three add powers, resulting in 183 unique designs. Possibly a strategy like this along with other creative approaches that take pupil size variations into account will help increase patient success with multifocal lens wear. CLS

For references, please visit www.clspectrum.com/references and click on document #262.