GP insights

Large-Diameter GP Works Best for Corneal Transplant Patient

BY ANN LAURENZI-JONES, OD, FAAO

A 71-year-old patient was referred for a contact lens fitting of the left eye following a corneal transplant and cataract extraction for a large stromal scar secondary to a corneal ulcer. Uncorrected visual acuity six months post-corneal transplant OS was 20/125 and the best spectacle correction (MRx: +1.50 −2.50 × 125) was 20/60. The topography OS showed significant asymmetric and irregular corneal astigmatism.

The patient did not refract to good vision with spectacles, so we chose a GP lens to achieve the best corrected visual acuity.

A Large-Diameter GP Design

The GP lens that we chose was the Dyna Intra-Limbal (Lens Dynamics) lens. It has a large standard overall diameter (OAD) of 11.2mm that vaults the central and paracentral irregularities. The diameter is also large enough to allow the weight of the lens to bear outside of the graft-host junction, where a 360-degree running suture was still in place.

The final diagnostic lens ordered had a base curve of 7.42mm with a power of −3.00D, standard peripheral curves, and an overall diameter of 11.2mm. Although the visual acuity was improved over spectacles to 20/30+, centrally the fluorescein pattern revealed mild touch, there was very little movement and the edges were significantly tight with bearing at the graft-host junction and peripheral cornea (Figure 1).

Figure 1. Inadequate lens fit with tight edges and bearing at the graft-host junction.

We increased the optical zone (OZ) to 9.8mm to increase the sagittal depth and completely vault the central corneal graft. The 9.8mm OZ will also move the landing and transition to the periphery of the lens and outside of the graft-host junction, minimizing any bearing and risk of complications due to inflammation, which can lead to rejection. The peripheral curves were also significantly flattened, which allowed for adequate movement and tear exchange under the lens. The lens material was Optimum Extra (Dk = 100, Contamac), which we chose to minimize any hypoxia-related complications.

Post-Transplant Fitting Tips

Fitting post-corneal transplant patients can be challenging. A GP lens usually is the best option when a patient has significant irregularity on the corneal surface. The lens should have a large OAD to vault the central graft and avoid direct bearing on the graft-host junction. For a spherical lens, choose an initial base curve that is close to the average of the flat and steep keratometric readings; for this particular lens, use topography to choose the base curve closest to the measurement at the temporal 4mm to 5mm position. Although lenses on corneal grafts may not always center perfectly, there should be no areas of heavy bearing as well as adequate tear exchange under the peripheral curves.

I believe the Dyna Intra-Limbal lens is a great choice for postpenetrating keratoplasty patients because of its wide range of parameters. Base curves range from 5.92mm to 9.38mm. It is available in a bitoric or reverse geometry design, with customizable peripheral curves and powers of ±25.00D. The OAD can range from 10.0mm to 12.0mm, but the lens should be fit at least 0.2mm smaller than the iris diameter. It's important to use a lens that has extensive parameters when fitting post-graft patients as you never know what you will need. CLS