After RK, a graft may be required because of trauma resulting in incisional rupture; central scarring not responsive to phototherapeutic keratectomy; irregular astigmatism; contact lens intolerance; or progressive hyperopia. The RK incisions can gape or dehisce during penetrating keratoplasty trephination, preventing creation of an even, uniform, and deep trephination. One method for avoiding RK wound gape or dehiscence during keratoplasty is to mark the cornea with the trephine and then reinforce the RK incisions with interrupted sutures outside the trephine mark prior to trephination. If the RK incisions open during the corneal transplant surgery, then X, mattress, or lasso sutures may be required to close these stellate wounds.
Corneal transplantation may also be required after excimer laser surface ablation. However, because of the 6- to 8-mm ablation zones typically used, the corneal periphery is generally not thinned, and transplantation in this situation is usually straightforward.
After LASIK, corneal transplantation may be required to treat central scarring (eg, after infection or with a buttonhole) or corneal ectasia. A significant challenge in this scenario is that most LASIK flaps are larger than a typical trephine size (8 mm). Trephination through the flap increases the risk that the flap peripheral to the corneal transplant wound may separate. This complication may be avoidable through careful trephination and use of a gentle suture technique that incorporates the LASIK flap under the corneal transplant suture. Femtosecond laser trephination theoretically may decrease the risk of flap separation during trephination.
A few cases have been reported of inadvertent use of donor tissue that had undergone prior LASIK. The risk of this untoward event will increase as the donor pool includes more individuals who have undergone LASIK or surface ablation. Eye banks need to develop better methods to screen out such donor corneas. If a post-LASIK eye is inadvertently used for corneal transplantation, the patient should be informed. A regraft may be required to address significant anisometropia or irregular astigmatism.
Corneal transplantation is occasionally required in a patient with intrastromal corneal ring segments. The polymethylmethacrylate ring segments are typically placed near the edge of a standard corneal transplant, so the ring segments may be removed prior to grafting, or—because the ring segments lie within the central 7 mm of the cornea—they may also be left in place and removed in toto with the host tissue or removed at the time of trephination.
Though rare, corneal transplantation after laser thermokeratoplasty or conductive keratoplasty may be required. Trephination should be straightforward in such cases, and the thermal scars should generally be incorporated into the corneal button. Even if the scars are not incorporated and remain peripheral to the new cornea, they should not significantly affect wound architecture, graft healing, or corneal curvature.
Contact Lens Use After Refractive Surgery
Indications
Contact lenses can be used before and after refractive surgery. For example, a patient with presbyopia can use a temporary trial with soft contact lenses to experience monovision before undergoing surgery, thus reducing the risk of postoperative dissatisfaction. Contact lenses can also be used preoperatively in a patient with a motility abnormality (eg, esotropia or exotropia) to simulate expected vision after refractive surgery and to ensure that diplopia does not become manifest.
In the perioperative period, hydrophilic soft contact lenses can help promote epithelialization and reduce discomfort after surface ablation; they may also reduce the risk of flap dehiscence in the case
of a free cap or help decrease epithelial ingrowth following a flap refloat. Rigid gas-permeable (RGP) contact lenses are more effective than are soft lenses to correct reduced vision due to residual irregular astigmatism, and they can be a useful adjunct after RK and LASIK. Night-vision problems caused by a persistent, uncorrected refractive error or irregular astigmatism may also be reduced by using contact lenses. However, if the symptoms are related to higher-order aberrations, they may persist despite contact lens use.
General Principles
Contact lenses for refractive purposes should not be fitted until surgical wounds and serial refractions are stable. The most practical approach to fitting an RGP lens after refractive surgery is to do a trial fitting with overrefraction.
The clinician needs to discuss with the patient in understandable terms the challenges of contact lens fitting after refractive surgery and align the patient’s expectations with reality. A patient who successfully wore contact lenses before refractive surgery is more likely to be a successful contact lens wearer postoperatively than is one who never wore contact lenses.
Contact Lenses After Radial Keratotomy
Centration is a challenge in fitting contact lenses after RK because the corneal apex is displaced to the midperiphery (Fig 11-2). Frequently used fitting techniques involve referring to the preoperative keratometry readings and basing the initial lens trial on the average keratometry values. Contact lens stability is achieved by adjusting the lens diameter. In general, larger-diameter lenses take advantage of the eyelid to achieve stability. However, they also increase the effective steepness of the lens due to increased sagittal depth. If the preoperative keratometry reading is not available, the ophthalmologist can use a paracentral or midperipheral curve, as measured with postoperative corneal topography, as a starting point.
Figure 11-2 Fluorescein staining pattern in a contact lens patient who had undergone RK and LASIK shows pooling centrally and touch in the midperiphery. This pattern is the result of central corneal flattening and steepening in the midperiphery.
(Courtesy of Robert S. Feder, MD.)
When a successful fit cannot be obtained with a standard RGP lens, a reverse-geometry lens can be used. The secondary curves can be designed to be as steep as necessary to achieve a stable fit. The larger the optical zone, the flatter the fit.
Hydrophilic soft lenses can also be used after RK. Toric soft lenses can be helpful when regular astigmatism is present. Soft lenses are less helpful in eyes with irregular astigmatism because they are less able to mask an irregular surface. Newer lens designs such as hybrid contacts, which consist of an RGP center surrounded by a soft contact lens skirt, and scleral RGP lenses, which vault the cornea and contact the perilimbal conjunctiva/sclera, may be helpful for patients with significant irregular astigmatism who are intolerant of conventional RGP lenses.
Whenever contact lenses are prescribed for post-RK eyes, as in the preceding scenarios, the ophthalmologist should continue to monitor the cornea to check for neovascularization of the wounds. Should neovascularization occur, contact lens wear should cease. Once the vessels have regressed, refitting can commence.
Contact Lenses After Surface Ablation
Immediately after surface ablation, a soft contact lens is placed on the cornea as a bandage to help promote epithelialization and reduce discomfort. The lens is worn until the corneal epithelium has