Article

PRESCRIBING FOR ASTIGMATISM

WHEN REGULAR ASTIGMATISM GOES AWRY

The initial diagnosis of keratoconus (KC) can be difficult, especially in situations in which patients are asymptomatic. Recently, two young patients presented to our clinic with low amounts of astigmatism, slightly reduced visual acuity (VA) in one eye, and no history of KC. Below are some tests that helped us determine the proper diagnosis.

Tests for Diagnosis

Case History Patient A presented with a history of asthma, allergies, and occasional eye rubbing. Patient B reported no pertinent medical or ocular history. Neither patient reported a family ocular history of KC. Atopic conditions (e.g., asthma, eczema, allergies, and sleep apnea) have been associated with KC (Gordon-Shaag et al, 2015; Sharma et al, 2013; Gupta et al, 2012). Inquiring about these systemic conditions can assist in diagnosing KC.

In addition, Patient A reported difficulty driving at night. KC tends to affect low-contrast acuity (Zadnik et al, 1987), which may explain her concerns with nighttime driving.

VA Manifest refraction revealed slightly reduced VAs (20/20 to 20/25 range) in one eye of both patients. After ruling out any history of strabismus or amblyopia, we investigated other causes of reduced vision, such as dry eye and corneal irregularity.

Refraction A scissors reflex on retinoscopy is another indicator of corneal ectasia. Our patients demonstrated a scissors reflex with poor endpoints with retinoscopy. In addition, a highly inconsistent cylinder axis was noted on manifest refractions at different visits. While comparing previous prescriptions, a fluctuating cylinder prescription of approximately 0.75D with a varying range of cylinder axes were noted at several examinations (e.g., we noted cylinder axes ranging from 25° to 90° for Patient A).

Slit Lamp Biomicroscopy In earlier stages of ectasia, it may be difficult to note corneal signs such as Fleischer ring, Vogt’s striae, or corneal thinning. So, relying solely on corneal signs may not be sufficient. Neither patient revealed any pertinent corneal findings on slit lamp examination that may be indicative of KC.

Topography Topography revealed bilateral superior forme fruste KC for Patient A and bilateral inferior KC for Patient B (Figures 1 and 2). Once the KC diagnosis is confirmed, discuss the prognosis and management options with patients and their families. Corneal cross-linking (CXL) should be considered for young KC patients, who are at a greater risk for progression; CXL strengthens the cornea and reduces progression of keratoconus (Spoerl et al, 1998; Mohammadpour et al, 2017).

Figure 1. Topography of patient A depicts bilateral superior steepening.

Figure 2. Topography of patient B demonstrates inferior steepening classic of keratoconus in the right eye (left), and the left eye shows irregular astigmatism with slight inferior steepening (right).

In Conclusion

Corneal or scleral GP contact lenses can be helpful for providing optimal and consistent vision for patients who have irregular corneas. An in-depth conversation about visual demands, vocation, and avocations can help narrow down a specific lens modality that would provide visual rehabilitation to patients and improve their quality of life. CLS

For references, please visit www.clspectrum.com/references and click on document #283.