BEFORE FITTING A PATIENT with contact lenses following a corneal transplant, a myriad of factors must be considered. Characteristics including transplant age and health, previous contact lens wear, and the patient’s visual goals and capabilities all contribute to determining the best modality for a patient. This article will first review many of the factors to assess when beginning the contact lens fitting process for a patient who had a corneal transplant, and then move into the intricacies of fitting corneal and scleral lenses after a penetrating corneal transplant.

PRE-FITTING CONSIDERATIONS

The age and health of a corneal transplant will dictate whether that transplant can successfully wear a contact lens. Following the transplant surgery, it may be three to six months, or longer, before a patient’s transplant is deemed ready for contact lens wear. Suture removal following surgery typically is delayed for four to six months time with the primary goal of reducing corneal astigmatism and irregularity.

During this time, a few sutures may be removed at each appointment while the patient is monitored every few weeks to evaluate vision, refraction, and corneal topography. This is repeated until either the corneal astigmatism has been reduced to a manageable level or all the sutures have been removed. For contact lens fitting, waiting until the suture removal process has been completed is best, as the corneal shape will be more stable. If some of the sutures are not removed, fitting over the sutures is acceptable as long as they are not bearing on the contact lens, as it could result in a broken suture or an inflammatory response.

Performing a comprehensive corneal health evaluation prior to contact lens fitting and throughout the process is imperative to ensure that no harm occurs to the new tissue. Starting at the surface of the cornea, epithelial integrity and regularity should be monitored closely. A corneal transplant may have a more fragile epithelium, making it more susceptible to sloughing or erosion and increasing the risk for microbial keratitis. The presence of stromal scarring or haze should be documented for future reference and evaluated as possible edema or rejection.

Endothelial cell evaluation for guttata to gauge the risk of decompensation and transplant failure down the road is beneficial. Additionally, evaluation for the presence of keratic precipitates—indicating active endothelial rejection—should be completed. The presence of corneal vascularization after a transplant also increases the risk for rejection and must be closely monitored. The extent of vascularization around and within the transplant should be meticulously measured and notated for future comparison.

Along with a diligent slit lamp examination, many instruments may be utilized to provide further analysis. External photography can be helpful for documenting a host of findings before and during the contact lens fitting process, allowing for more detailed comparison. Findings such as epithelial staining, stromal edema, corneal haze, and neovascularization should be photo-documented prior to fitting and throughout the fitting process, allowing for side-by-side comparison.

Baseline endothelial cell count and corneal pachymetry should be obtained (Figure 1). A transplant that has an endothelial cell count below 800 cells/mm² is considered high risk for corneal edema and potential transplant failure, and may have a better result with a corneal GP lens compared to a scleral or thicker custom soft contact lens.¹ Tracking corneal edema with pachymetry, especially global pachymetry, allows the fitter to monitor the corneal response to the stress of contact lens wear, helping to determine whether a particular contact lens modality is safe for the patient.

Evaluating the corneal and scleral shape with corneal and scleral topography or profilometry can be very helpful when fitting a corneal transplant (Figure 2). With these technologies, practitioners can more accurately assess the shape of the graft, the graft-host junction, the corneal-scleral junction, and the scleral shape.

When evaluating the corneal topography data, directly assessing the elevation data can provide more insight as to the true shape of the ocular surface and can assist in determining what lens modality may be best for the patient. For example, Zheng and colleagues found that when considering a corneal or scleral lens, eyes that had elevation differences greater than 350 microns across the corneal surface had a higher success rate with a scleral lens compared to a corneal lens.² Beyond the cornea, conjunctival irregularity due to scarring or the presence of glaucoma drainage devices, pterygiums, or pinguecula can increase the difficulty of fitting scleral lenses, and a corneal GP design could be considered.

Similar to other contact lens wearers, patient characteristics play a big role in determining what lens modality with which a patient is most likely to succeed. For patients who wore contact lenses prior to corneal transplantation, being able to return to the same modality following surgery can be an easier transition as they are already familiar with the care, handling, and comfort of that lens style. Also, if the patient wears a contact lens in the fellow eye, keeping that same modality for the transplant eye can be simpler for the patient.

Other considerations, such as a patient’s mobility and dexterity of his or her hands, fingers, head, neck, and back, may rule out certain lens modalities due to handling capabilities. Finally, learning the patient’s visual requirements and goals can also help in determining which modality to pursue.

LENS DESIGN SELECTION

Following a comprehensive health assessment and clearance from a corneal surgeon, the next step in corneal transplant management is to optimize vision. While some full-thickness corneal transplants may result in a relatively normal corneal shape and the patient may be able to wear glasses or soft contact lenses, the majority will require GP lens optics for best visual function.

Design selection largely depends on the regularity of the corneal transplant. Mild-to-moderate surface irregularity would allow for the stable fit of a smaller-diameter GP lens, but more significant surface irregularities, like “proud” bulging grafts, tilted grafts, or recurrent keratoconus in a transplant, would likely require a larger-diameter GP lens, such as a scleral design, to result in a successful fit.

Corneal GP Lenses Corneal GP lenses are typically designed in a reverse geometry shape to accommodate the steepened cornea peripheral to the graft-host junction. When selecting a lens design, many laboratories have sets specifically made for penetrating corneal transplants. Rarely, a lens will fit both the graft and host tissue shape immediately from the fit set. There may be a need to try on a few lenses, to assess both the central and peripheral cornea with various lenses. Designs that can change the base curve diameter to accommodate various graft sizes are also helpful.

When assessing the lens-cornea relationship, there is no “perfect” post-photorefractive keratectomy fit. In general, look for central alignment to mild clearance with sodium fluorescein, as the central graft may be somewhat sunken in shape. Over the graft-host junction, an ideal appearance is a feathery touch that has good tear exchange with the blink.

Typically, the graft-host junction is the most elevated area of the cornea, and it will bear the weight of the corneal GP. The goal of a corneal GP fitting on an eye with a corneal transplant is to balance central clearance and mid-peripheral bearing. Excessive central clearance will lead to bubbles in the optical zone, whereas excessive bearing will cause epithelial breakdown over the graft-host junction. Next, an average edge clearance is desired to allow for sufficient tear exchange and prevent lens binding (Figure 3).

The final steps in the lens fitting are to assess the lens centering, lid interaction, and power determination. If the graft is very irregular or tilted, the lens is prone to center over the area of highest corneal elevation, which isn’t always the central cornea. If decentration of the lens is caused by the cornea shape and it is affecting visual acuity, consider a larger overall diameter to make an impactful design change. If the eyelids are causing decentration, occasionally a smaller-diameter lens can improve the fit.

As for power determination, spherical lens powers are the best approach in these cases. If the patient has significant astigmatism in an over-refraction, perhaps from a toric intraocular lens (IOL), a front toric scleral lens may be the best option for vision correction. Glasses to be worn over the corneal GP lens would also be an acceptable approach. A front toric corneal GP lens is available, but the thickened edge of the prism ballast may lead to lens stability challenges on these irregular corneas.

Corneal GP lenses provide an excellent environment to promote long-term corneal health. However, there are complications to be aware of, like corneal staining, gaping of the graft-host junction, dellen, and conjunctival irritation due to a decentered lens. When corneal staining is observed, the determination must be made whether the source is from the lens fitting too tightly and binding down on the cornea, or whether the fit is too shallow and causing surface breakdown from lens bearing.

If there is a gape in the junction between graft-to-host tissue, this would need to be reevaluated by the corneal surgeon, and lens wear should be halted until it is addressed. Dellen and conjunctival irritations can be observed due to the high irregularity of these ocular surfaces. Continual adjustment in lens size and shape, as well as copious surface lubrication, are the best steps to address such findings. When these complications cannot be resolved, leading to a compromised cornea due to a poor fit, a scleral lens would be an excellent remedy in most cases.

Scleral Lenses As previously noted, corneal transplants can result in irregular corneal elevations, leading to distorted vision and irregular astigmatism. Large-diameter scleral lenses have the ability to vault the entire cornea, providing a smooth optical surface, compensating for corneal irregularities, and offering improved visual acuity for post-surgical patients. By creating a tear-filled reservoir between the lens and the cornea, scleral lenses mask irregularities and reduce visual distortions.

Scleral lenses are known for their exceptional comfort and stability. The fluid reservoir between the lens and the cornea provides a hydrating environment, relieving dryness. This is particularly beneficial for patients who have corneal transplants, as they often experience dry eye symptoms due to decreased corneal sensation and tear production. The tear-filled space also acts as a protective cushion, reducing friction and irritation on the corneal surface. Additionally, the scleral lens design provides excellent stability, minimizing lens movement and ensuring consistent vision throughout the day.

Fitting scleral lenses on patients who have corneal transplants requires a highly individualized approach. Scleral lens practitioners must consider the unique characteristics of each transplant, such as graft size, shape, and location, in order to achieve an optimal fit and maximize the visual outcome. Special attention should be given to the post-transplant corneal curvature and elevation, the integrity of the graft, the presence of sutures or other ocular conditions, and the graft-host junction.

Through detailed corneal topography and advanced diagnostic measurements, scleral lens practitioners can customize scleral lenses to match the specific needs of each graft, ensuring a comfortable fit and optimal visual correction. Often, an oblate-shaped scleral lens design is required for post-graft corneas due to their reverse geometry shape to ensure that the graft-host junction is properly vaulted without touch or erosion. However, some proud grafts may still require a prolate design, so it is important to analyze the shape of each graft with elevation maps. Due to scleral lenses aligning with the sclera and conjunctiva, even the most uniquely shaped grafts can be fit with stability compared to a corneal GP lens, which may decenter, as previously discussed, due to excessive edge clearance or bearing on higher elevation points of the graft.

While scleral lenses offer numerous benefits for patients who have corneal transplants, it is important to acknowledge and address potential complications that may arise. The fit and design of scleral lenses are critical factors in mitigating these challenges. Scleral lens practitioners and corneal surgeons should closely monitor their patients to provide appropriate guidance and care to ensure optimal outcomes.

One potential complication that can occur with scleral lenses in patients who have corneal transplants is the development of epithelial bullae. They can cause discomfort and reduced visual acuity, and may lead to corneal abrasions or erosion. Epithelial bullae can occur due to inadequate tear exchange under the lens, excessive lens bearing on the cornea, excessive clearance over the graft, suction, or improper lens fit.

Practitioners must carefully assess the lens fit and make necessary adjustments to minimize the risk of epithelial bullae formation. Often the use of anterior segment optical coherence tomography (OCT) can be helpful in the diagnosis and monitored progression of bullae formation.

Another potential concern for patients who have corneal transplants is graft rejection. While scleral lenses themselves do not directly cause graft rejection, improper lens fit or prolonged lens wear can lead to corneal hypoxia and compromise the health of the donor tissue. Michaud and colleagues determined that to provide sufficient oxygen to the cornea and avoid central corneal edema, a scleral lens must be no greater than 250μm thick, manufactured from the highest Dk material available—ideally greater than 150—and fit so that vault is no more than 200μm.³

It is crucial to monitor corneal health and graft stability during regular follow-up visits. Any signs of graft rejection, such as corneal edema, increased vascularization, or graft infiltrates, should be urgently addressed and co-managed with the patient’s corneal surgeon (Figure 4). Patients should be monitored with anterior segment photography, anterior segment OCT, pachymetry, and endothelial cell count before and during lens wear to look for any early signs of graft rejection. Optometrists should educate patients on the clinical signs and symptoms of graft rejection and emphasize the importance of regular monitoring to ensure early detection and intervention.

IN CONCLUSION

Patients who are wearing newly fit lenses on corneal transplants should be monitored closely for the first year, with corneal evaluations being performed about every three months. Once a healthy and stable fit is established, a corneal evaluation is recommended every six months. With proper care, guidance, and ongoing evaluation, GP lenses can provide enhanced vision and comfort for patients who have corneal transplants, improving their quality of life and visual function. CLS

References

1. Walker MK, Bergmanson JP, Miller WL, Marsack JD, Johnson LA. Complications and fitting challenges associated with scleral contact lenses: A review. Cont Lens Ant Eye. 2016 Apr;39:88-96.
2. Zheng F, Caroline P, Kojima R, Kinoshita B, André M, Lampa M. Corneal elevation differences and the initial selection of corneal and scleral contact lens. Poster presented at the 2015 Global Specialty Lens Symposium, Las Vegas. January 2015.
3. Michaud L, van der Worp E, Brazeau D, Warde R, Giasson CJ. Predicting estimates of oxygen transmissibility for scleral lenses. Cont Lens Ant Eye. 2012 Dec;35:266-271.