contact lens practice pearls
The Phoropter: Friend or
BY THOMAS G. QUINN, OD, MS, FAAO
We generally view the phoropter as a device of convenience. But sitting behind this mainstay of the ophthalmic examining lane may seem dark and intimidating for patients. What role does
this instrument play when fitting specialty-design contact lenses?
The phoropter can prove immensely helpful when fitting an astigmatic patient with contact lenses. The instrument can contribute even before you apply the first lens. When completing the subjective refraction, tell the patient, "I'm finding that you have astigmatism. We'll talk more about what that is, but first, as you watch the chart at the end of the room, I'm going to take the astigmatism correction out of this instrument so you can see how it affects your vision."
After you remove the cylinder lenses, the patient will invariably report, "My vision is blurry." Reinsert the lenses into the
phoropter. The patient will report, "My vision is clear again." You have convincingly demonstrated why it's important to correct the astigmatism. The patient will now understand why he needs a GP or toric soft contact lens and he will prove more willing to work with you and pay the additional fees associated with fitting a more specialized contact lens design.
Assessing Subjective Response
The final refraction can help you assess the patient's visual sensitivity in two ways:
1. Rotate the cylinder in the phoropter and ask the patient to report when the letters on the chart begin to blur. If he reports blur after only a few degrees of rotation, then realize that he may not tolerate the small amounts of axis mislocation that commonly occur with toric soft contact lenses. A GP contact lens may provide a better choice.
2. After returning the axis to its proper orientation, reduce the cylinder lens power and ask the patient to report when he first notices blur. (The goal here is to identify the lowest cylinder power that will still provide clear vision. Specify this power when designing a toric soft contact lens.) Rotational instability of low cylinder power lenses is less disturbing to vision than rotation of higher toric powers.
The phoropter can provide great assistance when the toric contact lens wearer complains of consistently blurred vision. Fluctuating vision is a signal that the contact lens isn't stable, so be cautious if this is the case. Attempting an over-refraction over an unstable contact lens is an exercise in frustration.
If the fit is stable, then the over-refraction should prove fairly straightforward and provide a clear endpoint. You can then combine it with the on-eye contact lens power and observed rotation of the lens to calculate a new toric lens power (see "Turn Tedious Over-Refraction Into a Focusing Friend" in the April 2003 issue of Contact Lens Spectrum).
Avoid using a phoropter to refract over a simultaneous vision multifocal contact lens. Doing so may alter pupil size and accommodative response in an unnatural way, misleading you as you attempt to determine the optimal lens power. Grab the loose lenses instead -- they're easy, effective and allow you to bring the patient out from behind the shadowy confines of the
phoropter. You and your patients will enjoy seeing the light!
Dr. Quinn is in group practice in Athens, Ohio, and has served as a faculty member at The Ohio State University College of
Contact Lens Spectrum, Issue: March 2005