THE FITTING STABILITY of scleral contact lenses makes them ideal for adding prism to aid patients who have binocular vision dysfunctions.

CASE #1

A 63-year-old female patient was referred for a contact lens fitting. She presented with a history of laser-assisted in situ keratomileusis (LASIK) 20 years prior, dry eye, anterior basement membrane dystrophy, and esotropia.

Her manifest refraction was +1.25 –1.25 x 136 20/20 OD and +1.00 –1.75 x 076 20/20 OS. Testing revealed a mild alternating esotropia. She was able to fuse with two prism diopters (PD) base out (BO). Scleral lenses were recommended to manage her residual ametropia, dry eye, and diplopia.

The patient was fit with 16.5mm scleral lenses (hexafocon A). The right and left lenses had 179 microns and 118 microns back-surface landing zone toricity, respectively, and each lens had 1PD BO. At dispense, the patient’s visual acuity measured 20/20 in the right and left eyes with single binocular vision.

At follow-up, she reported mild diplopia with the lenses. Testing revealed that the right lens had minimal central clearance and an over-refraction that measured +0.50. An additional 1PD BO prism held over the right eye improved fusion and binocular comfort. A replacement exchange lens was ordered with an updated power, an increase in sagittal depth of 200 microns, and 2PD BO prism. The lens adjustments gave the patient successful 20/20 visual acuity in both eyes with binocular fusion.

CASE #2

A 56-year-old keratoconus patient, post-corneal transplant OS, was referred for scleral lens fitting. He had a history of binocular vision dysfunction, and his manifest refraction was –7.00 –4.50 x 050 20/70 OD and –7.00 –4.50 x 070 OS. The patient was fit with 17mm free-form scleral lenses, which improved his vision to 20/40 OD and 20/25 OS. With the rotational stable lens in place the patient was able to fuse 4PD base up (BU) OS. An exchange pair of lenses was ordered with the prism that was split incorporating 2PD BD OD and 2PD BU OS (Figure 1).

Unfortunately, the patient had persistent diplopia with the prismatic scleral lenses. Prism trial lens testing over his scleral lenses showed that an additional 6D of BU prism in front of his left eye was necessary for fusion. Although more vertical prism could be added to his scleral lenses, instead the patient was prescribed a pair of progressive addition spectacles with a +2.50 add and a split amount of additional 3PD BD right and 3PD BU left to wear over his prismatic scleral lenses. Even though he wasn’t successful with prism-only correction in his scleral lenses, the 4D of scleral lens prism did allow for less prism for his over-spectacle that additionally gave him power for reading.

DISCUSSION

Scleral lenses can incorporate 4PD to 5PD amounts in each eye for either vertical or horizontal prism correction (Vincent and Fadel, 2019). Additionally, custom landing zone designs are necessary to match the scleral profile to achieve rotational stability.

REFERENCE

1. Vincent SJ, Fadel D. Optical considerations for scleral contact lenses: A review. Cont Lens Anterior Eye. 2019 Dec;42:598-613.