prescribing for astigmatism
Astigmatism and Refractive Surgery
BY WALTER L. CHOATE, OD, FAAO
Most practitioners who actively co-manage refractive surgery patients have seen their share of less than optimum visual results, even with highly skilled surgeons. This has as much to do with patient expectations and demands on their visual systems as with the results of the procedure itself.
Uncorrected astigmatism, even in small amounts, can become a significant post-op challenge for the co-managing practitioner. Also, as more patients present with refractive surgery complications, do not underestimate the impact of corneal physiology problems on refractive error.
The Patient Presents
A 34-year-old white male was referred to our office by a local MD. He underwent eight-incision RK/AK 10 years prior. The patient had poor uncorrected vision and experienced dry eyes with slight redness on most days. He'd worn various types of hydrogel contact lenses, and his current prescription for CIBA Focus Torics was: OD 0.75 1.75 x 60 and OS 1.50 1.75 x 80.
The patient's uncorrected visual acuity (VA) was OD 20/100-2, OS 20/200. His corrected VA was OD 20/50, OS 20/60. Corneal topography revealed OD 40.12/ 42.25@135, OS 39.87/42.12@ 165.
I also discovered a 4.0mm treatment zone decentered supero-temporally OU and irregular corneal astigmatism central 5.0mm. His refraction was OD 1.00 1.50 x 65 20/30; OS 1.50 2.00 x 85 20/40. Slit lamp exam revealed 1+ bulbar hyperemia OU, 3+ limbal hyperemia OU, 1+ powdery scattered mid-peripheral and peripheral subepithelial infiltrates, as well as 3+ neovascularization of incisions.
Although this patient had multiple corneal and visual complications from surgery, the primary diagnosis in this case was long-term corneal hypoxia. Cessation of contact lens wear and return to spectacles is an excellent solution to this patient's problem, but he had no desire to wear spectacles even for a short period of time. Typically the best approach for this type of case is a rigid gas permeable (RGP) design.
However, I elected to first rehabilitate the patient's corneas. First-generation hydrogel lenses are contraindicated in these cases because of poor oxygen flow to the cornea. The only possible hydrogel material to consider for this patient is silicone hydrogel either Bausch & Lomb's PureVision (Dk/t 110) or CIBA Vision's Focus Night & Day (Dk/t 175).
Another challenge we face in this case is the amount of astigmatism the patient exhibits. Fortunately, the new silicone hydro gels are higher modulus lenses.
Treatment and Follow-up
We trial fit the patient with CIBA's Focus Night & Day lenses as follows: OD 1.25, OS 2.00.
At the two-week re-evaluation, the patient's ocular history consisted of much improved comfort and vision, and his eyes weren't as red. His corrected VA was OD 20/30 and OS 20/40. His over-refraction was OD plano 0.75 x 70 20/20 and OS +0.50 1.00 x 90 20/252 and his refraction OD was 1.25 0.75 x 75 20/202 and OS 1.50 1.25 x 92 20/253.
Slit lamp exam showed that corneal neovascularization appeared much improved with ghost vessels along several incision lines. I prescribed a fresh pair of Focus Night & Day: OD 1.25 and OS 1.75. Corrected VA was OD 20/25, OS 20/303.
This patient's chronic corneal edema had great impact on the astigmatic component of his refraction. It was in the patient's best interest to bring the cornea to baseline before prescribing a permanent contact lens fit.
Dr. Choate is in private practice in Nashville, TN, a charter member of the AOA Contact Lens Section and an adjunct faculty member at Southern College of Optometry.