Accurate Pupil Size Measurement

For Fitting SpecialEyes’ Multifocal Toric Contact Lenses .

Before fitting the 54 Multifocal contact lens, SpecialEyes strongly advises eye-care professionals to accurately measure the patient’s pupil size. The SpecialEyes Multifocal Simulator uses this measurement to ensure appropriate distribution of the custom multifocal optics over the pupil. The multifocal optic zones are designed to provide a good balance of vision within the setting the patient would most frequently wear the lenses. SpecialEyes recommends designing the multifocal optic zone sizes based on a patient’s effective pupil size measurement in regular room illumination, unless the patient’s work or preferences call for optimal vision in a different lighting condition. Providing an accurate pupil size measurement (within .1mm–.5mm) for the initial lens design greatly increases your patient’s chance of success, so we have listed some tools and tips below to help you achieve the best possible results.
 

image of Medmont topographer
Topography results from a Medmont Topographer.
The pupil measurement is listed under “Attributes”
and outlined in red.

Topographer

Most corneal topographers will automatically capture the patient’s pupil size. Please refer to your topographer’s user manual for specific details and instructions. SpecialEyes designs the 54 Multifocal optic zones based on the patient’s pupil size in regular room illumination. When using measurements obtained with a corneal topographer, it is crucial to account for the lighting of the room during the capture as well as the type of topographer, since some topographers use a light source that impacts the pupil size.

As an example, the Oculus Keratograph 5M Topographer emits a bright white light that will cause the pupil to constrict. The resulting pupil measurement will be smaller than it would be in regular room illumination. Therefore, when designing the multifocal optic zones based on this device’s measurements, we would need to assume a certain amount of dilation for an effective pupil size in regular room illumination.

On the other hand, the Medmont Topographer uses an infrared light source that should not influence pupil size; so in this case, the room lighting during the capture will be the primary variable. For example, when using the Medmont device in a brightly lit setting, the patient’s pupil will be more constricted and result in a smaller reading. Conversely, if the same patient were measured in a dimly lit setting, the pupils will dilate and produce a larger measurement. If you have any questions about designing a custom multifocal contact lens using a pupil size measurement from a corneal topographer, please contact our consultation department.

image of pupil gageRuler or Pupil Gauge

A ruler or pupil gauge offers an inexpensive and simple method to obtain pupil size measurements. However, using these tools requires special care to ensure the measurement is accurate. Begin by placing the ruler as close as possible alongside the eye, making certain not to tilt or bend the device. Have the patient focus straight ahead at an intermediate range spot to avoid accommodation. For optimal accuracy, take the measurement at the patient’s eye level and repeat each measurement two or three times to ensure the result is consistent.

If you are interested in receiving a SpecialEyes Pupil Diameter Ruler, please email your request to the SpecialEyes Team.

image of Volk eye check, ocular measurement deviceVolk Eye Check

The Volk Eye Check is an ocular measurement device that allows eye-care professionals to obtain repeatable and reliable pupil size measurements. When using the Volk Eye Check, try to avoid bright light from windows or mirror reflections that could influence the pupil size. The practitioner or technician should be at eye level and about arm’s length away from the patient. To ensure the most non-accommodative environment, the Volk device will direct the user to adjust the lighting or positioning if needed. In addition, the Volk Eye Check is an excellent device for measurement of HVID, lid positioning and sagittal height. To learn more about the device, visit the Volk Eye Check website.

image of infrared pupillometerInfrared Pupillometer

This handheld device takes very accurate and efficient monocular pupil size measurements. While most pupillometers instruct the user to dark-adapt the patient first, we recommend using regular room lighting. This is done by switching to a mode that uses no internal light source, often referred to as “dark” or “lights-off” mode. One of the most popular infrared pupillometers is the NeurOptics VIP-200.

When using this device, instruct the patient to look straight ahead with both eyes open. Then place the pupillometer over one eye at a right angle to the patient’s visual axis, making sure the other eye is exposed to the regular room lighting. To minimize tilting of the device, it is helpful to remain at the patient’s eye level. Press and hold the OD or OS button and wait for the video to be displayed on the LCD screen. While continuing to hold the OD or OS button, position the pupillometer so that the patient’s pupil is centered on the screen. The pupillometer will automatically detect and mark the pupil perimeter with a green circle. Once the green circle appears, the user may release the OD or OS button to begin the measurement. During the measurement, a bracket will appear. The pupillometer should be held firmly in position until the bracket disappears, signaling the measurement is complete. (NeurOptics Inc., 2015)