2020–2021 BCSC Basic and Clinical Science Course™
3 Clinical Optics
Introduction: Quick-Start Guide to Optics and How to Refract
Part 2: How to Refract
Step 2: Occlude 1 Eye
Occlude the Left Eye, Refract the Right Eye First
The next step is to occlude 1 eye in order to refract the patient’s other eye.
Barring exceptional circumstances, begin by occluding the left eye, so as to do the initial refraction in the right eye.
If you are using a phoropter, you may dial an opaque occluder into place using the accessory wheel (Figure I-23A).
If the patient is cooperative and will not find it too distracting, it is often preferable to occlude the nonrefracting eye with a plus lens, such as the +1.50 D retinoscopy lens (marked “R”) in the accessory wheel of the phoropter (Figure I-23B). This practice often better relaxes the accommodation of the eye you are refracting than occlusion of the fellow eye with an opaque occluder. However, this method will not work well on patients with latent hyperopia—first verify that the +1.50 D lens really does reduce the visual acuity. Dial in extra plus lens power if needed. This process is known as fogging. If you suspect hyperopia, attempt to relax accommodation by gradually dialing in plus sphere power, 1 click (0.25 D) every 15–20 seconds while talking amiably with the patient, until the visual acuity is substantially reduced.
Figure I-23 Occluding the right side of the phoropter: A, opaque occluder. B, +1.50 D “R” accessory lens. Notice the settings of the accessory wheel for the right eye, at the top left of the photos.
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.