When prescribing SpecialEyes custom toric contact lenses it is important to achieve a repeatable over-refraction. Use the SpecialEyes over-refraction...
Toric Multifocal Contact Lenses and Importance of Accurate Pupil Size Measurement
When fitting SpecialEyes' custom toric multifocal contact lenses, it is imperative to provide SpecialEyes with an accurate pupil size measurement. See why!
Analysis of pupils in clinical practice is typically performed within entrance skills examination for afferent pupillary defect, pupil size, and regularity. Pupil size may be estimated or measured with a common PD ruler for both scotopic and photopic conditions. This is important in the evaluation for anisocoria and overall neurologic function.
From a contact lens standpoint pupil size can take on another meaning as the pupil is our way of measuring how light is capable of entering the eye. When dealing with traditional soft spherical and toric contact lenses optic zones remain relatively large, at 8mm for a -3.00 D lens, in comparison to the typical human pupil. Once sphere or toric multifocal contact lenses contact lenses are selected, the light is separated out into zones of distance, near and/or intermediate power. As the optics separate out into their respective zones, evaluation of pupil size becomes particularly important as zone sizes decrease relative to a single vision lens. The central near zone of an aspheric multifocal contact lens may be in the order of 2.3mm surrounded by distance power, thereby confirming the need to ensure the patient has a pupil large enough to support the distance power in the periphery.
This may explain why certain patients are not able to achieve better vision despite best attempts to over refract them in office.
In custom soft multifocal contact lenses, like those offerings from SpecialEyes, central zone size may be specified as fine as 0.1mm steps and made available in center distance or center near options. In SpecialEyes’ custom aspheric multifocal contact lens design, the 54 Multifocal, the rate of power progression and the distance at which full power is reached in the periphery are also customizable by 0.1mm increments.
It is the fine incremental adjustments to the custom multifocal optic zones that lead to the importance of accurate pupil size measurement in practice. The traditional methods of PD ruler or pupil gauge may assist as long as the practitioner takes special care in measurement. Other methods may include the ruler built within corneal topography systems or infrared pupilometry.
When fitting SpecialEyes’ custom sphere or toric multifocal contact lenses, an accurate pupil measurement provided to the SpecialEyes consultant is critical especially when a multifocal zone change is being considered as a means to address your patient’s chief visual complaint.
Please refer to the SpecialEyes fitting guide(s) for specific recommendations on where to begin with their custom sphere or toric multifocal contact lenses, and ask their consultation staff for further information on troubleshooting multifocal contact lenses as it relates to pupil size should the need arise.
Matthew Lampa, OD, FAAO
Dr. Lampa is an Associate Professor of Optometry at Pacific University and a consulting optometrist to SpecialEyes.