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Bitoric lenses achieve comfortable fit for patients with pellucid marginal corneal degeneration
Corrected vision in eyes with PMCD was two lines better with bitoric gas-permeable contact lenses than with spectacles.
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Patients with pellucid marginal corneal degeneration may experience a comfortable and visually successful fit with bitoric gas-permeable contact lenses, according to Charles E. Dominguez, OD, and colleagues.
Dr. Dominguez, along with Arti Shah, OD, and Barry A. Weissman, OD, PhD, conducted a retrospective review of 11 patients who were diagnosed with pellucid marginal corneal degeneration (PMCD) and fitted with bitoric gas-permeable lenses.
“Corrected vision in eyes with PMCD improved approximately two lines with bitoric gas-permeable contact lenses compared to that achieved with spectacles,” the study authors said, describing their results in Eye & Contact Lens.
The patients’ charts were reviewed for use of diagnostic contact lenses at the first visit, number of office visits, uncorrected visual acuity, best corrected visual acuity and contact-lens-corrected acuity. The researchers also recorded contact lens successes and failures and assessed contact lens complications.
Bitoric lenses have a toric power on the front surface and a toric curvature on the back surface that conforms to the curvature of the patient’s cornea. They are generally used in patients with 2.5 D or more of astigmatism.
Against-the-rule astigmatism
Image published with permission of Eye & Contact Lens. |
PMCD is a non-inflammatory ectatic disorder of the inferior peripheral cornea, often characterized by flattening of the vertical meridian and against-the-rule astigmatism, according to the authors.
“The cause of PMCD remains obscure, but it is believed to be a variant of, and is often compared to keratoconus,” they said. “Essentially, it can be considered a low hanging cone with thinning inferiorly.”
Due to the against-the-rule astigmatism associated with PMCD, conventional rigid gas-permeable lenses often do not provide enough stability for visual acuity, Dr. Dominguez and colleagues said.
Soft toric contact lenses may provide good vision for patients in their early stages of PMCD, but become ineffective as the disease progresses, they said.
“The success of bitoric gas-permeable contact lenses for patients with PMCD can be attributed to improved tolerance because of enhanced mechanical fitting allowed by the back cylindrical gas-permeable contact lens surface,” they said.
Analysis results
The review of a cohort of 11 patients with previously diagnosed PMCD showed that bitoric lenses could be a good fit for patients with the disease.
Of the 11 patients studied, only one did not meet the criteria for contact lens success during a 4-month follow-up, and two patients experienced giant papillary conjunctivitis.
Seven of the patients were fitted with bitoric gas-permeable lenses in both eyes, and one eye was chosen for review with the flip of a coin. The other four patients received one bitoric lens, and that eye was reviewed for the analysis, the authors said.
The patients’ mean uncorrected visual acuity was 20/181 and the best corrected spectacle visual acuity was 20/34. Best contact-lens-corrected acuity, however, was 20/22, according to the authors.
Why it works
Gas-permeable contact lenses will always follow the path of least resistance, the investigators said. In the case of PMCD, that means they would follow a path across the horizontal meridian. Bitoric gas-permeable contacts have a horizontal toric meridian that helps enhance stability and minimize lens rock, according to the authors.
They concluded that bitoric gas-permeable contact lenses are indicated as an initial diagnostic trial lens for patients with PMCD.
Ideally, a lens in this case should ride under the lid and show inferior touch and superior arcuate touch with a fluorescein pattern analysis, the authors said.
Based on clinical experience, the authors recommend bitoric gas-permeable contact lenses with a larger overall diameter for patients with PMCD to improve optical performance and enhance comfort, they said.
For Your Information:Reference:
- The corresponding author for this study is Barry A. Weissman, OD, Jules Stein Institute, 100 Stein Plaza, David Geffen School of Medicine at UCLA, Los Angeles, CA 90024; e-mail: weissman@jsei.ucla.edu.
- Dominguez, CE, Shah A, et al. Bitoric gas-permeable contact lens application in pellucid marginal corneal degeneration. Eye Contact Lens. 2005;31(5):241-243.
- Daniele Cruz is an OSN Staff Writer who covers all aspects of ophthalmology.