Patients requiring horizontal prism correction in their spectacle lenses are often told that there are no available contact lens options that can correct for their ocular misalignment and liberate them from glasses wear. Examples of some conditions that may create horizontal binocular misalignment include decompensating phoria, small angle strabismus, and congenital fourth nerve palsy.

Contact Lens Options for Vertical Prism

Many commercially available soft toric lenses and rigid GP lenses utilize prism ballasting, a technique in which prism is added by thickening one edge of a contact lens, to achieve rotational stability. The thicker edge naturally rotates toward the 6 o’clock position due to gravity, and as a result, prism correction in soft lenses and corneal GPs is limited to a base down orientation.

Up to 4 prism diopters (PDs) of base down correction can be incorporated for patients who have vertical deviations alone. Patients who have horizontal deviations, however, still face the dilemma of inadequate lens stability necessary to incorporate base in or base out prism correction.

Scleral Lens Options for Horizontal Prism

With the wide landing zone and semi-seal of a scleral lens, it is much more feasible to achieve the lens stability sufficient for incorporating horizontal prism into a contact lens. For a patient who has scleral toricity, it is possible to adequately orient and stabilize a lens to include up to 4PD of horizontal prism.

Given that significant scleral toricity may not be guaranteed for every patient, the best way to achieve the most stable scleral lens fit is by utilizing impression molded scleral lenses. Because of the steady lock-and-key fit, these lenses can integrate up to 4PD to 5PD of prism correction in any meridian. Once the factor of stability is resolved, the limiting factors for the amount of prism correction that can be incorporated into a scleral lens then become patient discomfort and oxygen permeability concerns with a thicker lens.

Case Report

A 67-year-old Caucasian male presented with a chief complaint of constant diplopia and visual field deficits after a motor vehicle accident and subsequent stroke. He was evaluated by a binocular vision clinic, and new spectacles that had 2 base out prism in each lens helped the patient achieve single vision.

This patient has high myopia and was a long-time monovision GP lens wearer prior to his motor vehicle accident. Preferring the visual comfort of contact lenses over spectacles, he was highly motivated to return to contact lens wear and inquired about prism correction options. He was referred to our clinic for a prismatic contact lens fitting. Using impression-based scleral lenses, we incorporated 2 base out prism into each lens to match the patient’s spectacle correction (Figure 1).

Upon initial lens application, the patient appreciated comfortable single vision. The patient stated his vision felt more comfortable in the contact lenses and he was able to walk around more steadily despite his visual field defects. Given the patient’s high-minus prescription, the contact lenses helped remove the peripheral aberrations he had with glasses that contributed to his difficulties with mobility. After successfully resolving the diplopia with a prismatic scleral lens fitting, we referred the patient to the low vision clinic for Peli prism fitting to aid with overcoming the visual field deficits from homonymous hemianopsia. CLS