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    Considering scleral lenses for astigmatic patients

     

    For many athletes, lens stability is essential, and scleral lenses are an excellent option. Unlike the majority of soft toric lenses or corneal GP lenses, scleral lenses tend to retain their physical and optical stability despite the rapidly changing ocular movements required while participating in athletic endeavors. Additionally, a large part of the ocular surface is shielded from foreign bodies during these demanding activities, such as dust or dirt exposure.

    Generally, a spherical scleral lens can easily compensate up to 3.50 D of regular corneal astigmatism.10 In this case, the coupling of a larger optical zone with a spherical optical surface offers the clear and stable world that are sought after by patients. If residual astigmatism is detected, front toric optics can be incorporated to further deliver improved visual performance. According to a study in a population of asymptomatic contact lens wearers, large diameter rigid gas permeable lenses can be a good alternative to soft toric lenses for the correction of refractive astigmatism.11

    In addition to athletes and patients with high amounts of corneal astigmatism, another prime scleral lens candidate can be a patient who is intolerant of corneal GP lenses despite the absence of an irregular cornea. Patients who experience dry eyes, fluctuating vision, GP lens dislocation, or GP lens nonadaptation appreciate the comfort afforded by scleral lenses.

    Whether the inability to adapt to GP lens wear is due to 3 o’clock and 9 o’clock staining secondary to lens rocking or simply corneal hypersensitivity, these fitting challenges are largely eliminated with scleral lenses. Moreover, the lid-lens edge interaction is drastically diminished after a scleral lens settles into conjunctival plane, which is one of the many reasons scleral lenses offer a more comfortable wearing experience.11

    With proper patient motivation and good lens handling techniques, it can be easy to transition patients to scleral lenses to improve lens comfort, maintain crisp and clear vision, and avoid spontaneous lens dislodgement.

    Fitting considerations

    A regular cornea patient with relatively large mesopic pupils and/or corneal-based higher order aberrations that exceeds population average may be more likely to complain of glare and haloes with her conventional contact lenses. Such patients may include those who have occupations that require night driving such as truck drivers and healthcare workers with night shifts. Scleral lenses offer more flexible customization in their optical zone widths as compared to conventional frequent-replacement soft lens designs. Consequently, symptoms of haloes and glare are reduced, along with a corresponding improvement in night vision.

    Allergies are increasingly prevalent and affect as many as 30 percent of adults and 40 percent of children.12 They are the fifth leading chronic condition in industrialized countries for all ages, and the third most common chronic disease in children under 18 years old. Many patients, who are frequently young and active, want to use contact lenses for vision correction and to improve their quality of life.13 Currently, eye-related allergies and contact lens wear affect increasing populations worldwide.13

    Scleral lens tear exchange is minimal after lens settling, which has been estimated at 0.2 percent per minute (Figure 3).14 The low rate of tear mixing can potentially reduce immunological and chemical mediators from entering a scleral lens, which may produce a prolonged period of comfortable wear on a daily basis during an allergy season. Conversely, the low tear exchange rate necessitates the selection of highly oxygen-permeable materials and a precise fitting algorithm to keep lens thickness and tear lens thickness as thin as possible,15 especially in healthy eyes (Figure 4).

    Clark Y. Chang, OD, MSA, MSc, FAAO
    Dr. Chang is a subinvestigator in numerous clinical trials. He is immediate past president of New Jersey Academy of Optometry, and an ...

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