Choosing a Modality: A Case History of Fitting an Irregular Cornea

by Rodney J. Smith, O.D., F.A.A.O., F.C.O.V.D., & Joseph D. Schwallie, O.D., M.S.
AUGUST 1999

Spectacles, thick soft lens, thin soft lens, rigid
lens. Find out which modality was preferred for this patient's irregular cornea.

Ulcerative corneal scarring can reduce visual acuity by causing an irregularity of the corneal surface or an altered arrangement of stromal collagen fibers, which results in the backscatter of light. If the exact cause of the visual compromise is unknown, you may be able to evaluate the corneal surface irregularity using computerized corneal topography.

Corneal topography continues to be used to evaluate normal, irregular and scarred corneas. Once you evaluate the topography of a scarred cornea, you may be able to use contact lenses to provide visual rehabilitation by effectively replacing the patient's irregular cornea with a new surface. The following case report illustrates an example where we improved a patient's corneal irregularity and decreased vision, which was a result of corneal scarring, when we fit her with contact lenses.

Initial Evaluation

Upon presentation for a routine contact lens check-up, the patient, a 31-year-old female, underwent the following examination procedures: ocular history, slit lamp biomicroscopy and photography, subjective manifest refraction, high and low contrast visual acuity at distance, keratometry and corneal topography.

After obtaining this baseline information, the patient's left eye was fit with a Cibathin soft contact lens (CIBA Vision), a Focus soft contact lens (CIBA Vision), and a PMMA rigid contact lens. Each lens was allowed to settle before the following testing was conducted: slit lamp evaluation of lens fit (including fluorescein photographs of the rigid lens), subjective overrefraction, high and low contrast visual acuity through the contact lens and corneal topography.

Baseline Data

The patient reported having decreased visual acuity in her left eye since being treated for a corneal ulcer 7 years earlier. Biomicroscopy showed a paracentral corneal scar approximately 2mm in diameter and located 2mm temporal to the line of sight in the left eye. Refraction was
-3.00DS. OD with acuity of 20/15 (high contrast) and 20/50 (low contrast). OS was -3.50 -0.50 x 103 with acuity of 20/20 (high contrast) and 20/60 (low contrast). Her keratometry readings were 42.50/43.50 @ 102 with clear mires OD and 43.00/43.25 @ 100 with clear mires OS. Corneal topography OS revealed an irregular area of corneal steepening located approximately 2.2mm from the line of sight at a 10- degree angle. Compared to other areas of the cornea located at an equal distance from the line of sight, the amount of steepening was approximately 3.50D.

(The three lens fits are summarized below):

Cibathin Soft Lens Data

Material: tefilcon; lens type: Group I; water content: 37.5%; center thickness: 0.035mm (at -3.00); diameter: 13.8mm; power: -3.50D. High contrast visual acuity: OS 20/20; low contrast visual acuity: OS 20/60; overrefraction: OS plano -0.50 x 150; corneal topography data: The lens seems to have a minimal effect on masking the irregularity, which may be due to its thin 0.035mm thickness.

Focus Soft Lens Data

Material: vifilcon A; lens type: Group IV; water content: 55%; center thickness: 0.10mm (at -3.00); base curve: 8.6mm; diameter: 14.0mm; power: -3.50D. High contrast visual acuity: OS 20/20; low contrast visual acuity: OS 20/60; overrefraction: OS plano -0.50 x 142; corneal topography data: The lens appears to mask the irregularity to a greater extent than the Cibathin lens. The center thickness of 0.10 mm may be partially responsible for this phenomena. The patient's subjective vision was similar between the two soft lenses.

Rigid Lens Data

Material: PMMA; center thickness: 0.15mm; base curve: 7.85mm; diameter: 9.6mm; power: -3.50mm. High contrast visual acuity: OS 20/15; low contrast visual acuity: OS 20/50. Subject's assessment of vision: vision with the rigid lens was reported as being substantially superior to both soft contact lenses and spectacles. Corneal topography data: The rigid contact lens appears to mask all of the irregularity and was able to restore visual acuity to 20/15. This indicates that the irregularity was responsible for the decrease in visual acuity.

Final Analysis

After achieving a successful fit with this patient, we reached the following four conclusions:

1 The majority of visual loss experienced resulted from the irregularity of the corneal surface, not from the loss of corneal clarity.

2Corneal topography was a useful tool in quantifying the corneal irregularity that was produced by the stromal scarring, and the changes associated with the various lens wear. Keratometry, however, was not very useful in this situation.

3The rigid lens was more effective at masking the corneal irregularity and restoring vision to 20/15, compared to either soft lens.

4The Focus soft lens (0.10mm center thickness) was able to mask more of the defect and provide better visual acuity than the Cibathin soft lens (0.035mm center thickness).

References are available upon request to the editors at Contact Lens Spectrum. To receive references via fax, call (800) 239-4684 and request document #51. (Be sure to have a fax number ready.)

Dr. Smith is a fellow of both the American Academy of Optometry and the College of Optometrists in Vision Development. He specializes in pediatric optometry and has lectured nationally and internationally in the field

Dr. Schwallie is a private practitioner in Toledo, Ohio and is a research consultant involved with contact lenses and ocular pharmaceuticals. His previous experience includes project management and optometric research within the Business Technology and Innovation unit at CIBA Vision.