contact lens case reports
Masking Irregular Astigmatism with Soft Lenses
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO
Patient WA underwent bilateral radial keratotomy in 1985 and subsequently underwent penetrating keratoplasty and trabeculectomy to the right eye in 1991 to correct his many post-RK complications. The right eye healed uneventfully, and his vision OD is 20/30 with a spectacle Rx of +1.75 3.50 x23.
Slit lamp exam of the left eye showed multiple radial incisions, many of which encroach into the papillary axis (Figure 1). A series of hexagonal incisions intersect the radial incisions, resulting in "T Cuts," which caused much of the irregular astigmatism noted in Figure 2. Best-corrected spectacle acuity OS was 20/100. Because WA was intolerant to GP lenses, he was referred to our practice for a possible custom soft lens.
Dispelling a Myth
Conventional wisdom dictates that soft contact lenses mask little or no regular and irregular astigmatism. This isn't always the case with the newer custom soft lens designs.
We fit WA with a custom post-refractive surgery soft lens, manufactured in a 59 percent water material with a central radius of 9.7mm and a peripheral "fitting radius" of 8.3mm. The lens diameter was 14.8mm, and the thickness over the central 8mm of the lens was 0.4mm. Figure 3 shows the photokeratoscopy over the surface of the lens that clearly shows that the 0.4mm-thick soft lens has indeed masked a significant amount of WA's regular and irregular astigmatism.
|Figure 1. Radial and hexagonal incisions OS.||Figure 2. Irregular astigmatism post RK OS.||Figure 3. Photokeratoscopy over the custom soft lens.|
Checking the Results
A manifest refraction over the contact lens revealed an Rx of 3.50 4.00 x62 with a best corrected visual acuity of 20/30. We appropriately adjusted the spherical power of the soft lens and corrected WA's residual cylinder OS with a spectacle Rx of +1.00 4.25 x65. He comfortably wears the lenses for 14 to 16 hours every day, but he's most delighted with his restored stereopsis, which had been lost for the past 20 years.
The 0.4mm center thickness helps maintain adequate on-eye lens movement, and the thin peripheral lens profile maximizes oxygen transmissibility to the limbus. Both of these features help to limit any potential neovascular response.
Until custom soft lenses are available in silicone hydrogel materials, our current hydrogel materials and diligent follow up will continue to serve us well.
Patrick Caroline is an associate professor of optometry at Pacific University and an assistant professor of ophthalmology at the Oregon Health Sciences University. Mark André is director of contact lens services at the Oregon Health Sciences University.