30OPTICS AND REFRACTION

79.What may cause monocular diplopia?

&Corneal or lenticular irregularity

&Decentered contact lens

&Inappropriate placement of reading add

&Transient sensory adaptations after strabismus surgery

&Distortion from retinal lesions (rare)

80.What conditions may give a false-positive reading with a potential acuity meter?

Macular scotomas in a patient with amblyopia or retinal disease, such as age-related macular degeneration. Acute macular edema also may elevate the reading, but the elevation disappears with chronic edema. An irregular corneal surface can falsely improve the potential acuity; however, wearing a contact lens may help.

81.What do you check when patients complain that their new glasses are not as good as their previous pair?

&Ask specifically what the complaint is. Distance reading? Near problems? Asthenopia? Diplopia? Pain behind the ears or at the nose bridge from ill-fitting glasses?

&Read the new and old glasses on the lensmeter and compare. Make sure that the old glasses did not have any prism. Check the patient for undetected strabismus with cover testing.

&Refract the patient again, possibly with a cycloplegic agent if the symptoms warrant.

&Check the optical centers in comparison with the pupillary centers.

&Check whether the reading segments are in the correct position-level with the lower lid.

&Make sure that the new glasses fit the patient correctly.

&Check whether the old glasses were made with plus cylinder by using the Geneva lens clock.

&Check whether the base curve has changed with the Geneva lens clock.

&Evaluate the patient for dry eye.

&If the patient has a high prescription, check the vertex distance. Often it is easier to refract such patients over their old pair of glasses to keep the same vertex distance.

&Check the pantoscopic tilt. Normally the tilt is 10–15 degrees so that when the patient reads, the eye is perpendicular to the lens. If the tilt is off, especially in relation to the old glasses, the patient may notice.

&With postoperative glasses, evaluate for diplopia in downgaze due to anisometropia.

&Perhaps the add is too strong or too weak. Check the patient using trial lenses and reading material.

&Sometimes if the diameter of the lens is much larger in the newer frames, the patient notices significant distortion in the peripheral lens. Encourage a small frame. However, too small a frame can make progressive bifocals very difficult. It is best to keep a frame size fairly consistent.

&Did the patient change bifocal types? Round top, flat top, executive style, and progressives all require different adaptations. Patients often have trouble when changing styles.

&Above all, try to test the new prescription in trial frames with a walk around the office. You do not want to go through this process again.

82.If after repeat refraction the patient suddenly develops more hyperopia than you previously noted, what do you look for?

A cause of acquired hyperopia, such as a retrobulbar tumor, central serous retinopathy, posterior lens dislocation, or a flattened cornea from a contact lens.