If the corneal lesion is superficial, it may be possible to scrape or peel it away without sharp dissection. Often, a smooth anatomical tissue plane anterior to the Bowman layer can be achieved with sweeping strokes parallel to the tissue through the use of a metal spatula blade or a cellulose sponge. In some cases, such as in Salzmann nodular degeneration, it is possible to gently peel the abnormal tissue off using a 0.12 forceps. When deeper dissection is required, the surgeon can either mark the area freehand with an adjustable-depth blade or use a trephine. A 2- to 3-mm disposable dermatologic skin punch trephine blade can be used to create a partial-thickness incision, and forceps and scissors are then used to excise a lamellar flap of cornea. The specimen is generally split into 2 pieces, or separate biopsies are taken, so that tissue can be sent for both histologic and microbiologic examination.
Alió JL, Agdeppa MC, Uceda-Montanes A. Femtosecond laser–assisted superficial lamellar keratectomy for the treatment of superficial corneal leukomas. Cornea. 2011;30(3):301–307.
Kron-Gray MM, Mian SI. Corneal biopsy. In: Basic Techniques of Ophthalmic Surgery. 2nd ed. San Francisco: American Academy of Ophthalmology; 2015:125–135.
The excimer laser can be used to remove superficial stromal tissue. However, abnormal tissue, like corneal scars or calcium deposits (as in band keratopathy), may ablate at a different rate than normal tissue, so an uneven surface results even if the original surface was smooth. Manual techniques are more likely to respect the Bowman layer and maintain a smooth ocular surface, as the laser does not respect anatomical planes. Frequent application of viscous liquid to the corneal surface during laser ablation can fill in gaps in the surface and help achieve a smooth surface after ablation. Most patients experience a hyperopic shift after phototherapeutic keratectomy (PTK) from the corneal-flattening effect of the procedure. Nevertheless, PTK is an excellent option in selected patients with superficial (less than 100 μm deep) stromal scarring or dystrophies when manual techniques are not feasible. PTK may postpone or eliminate the need for corneal transplantation. Topical MMC applied to the corneal ablation zone for a brief period following PTK has been shown to decrease postoperative scar formation. PTK can also be used to treat recurrent corneal erosion (see Chapter 4).
Hindman H, MacRae S. Phototherapeutic keratectomy. In: Basic Techniques of Ophthalmic Surgery. 2nd ed. San Francisco: American Academy of Ophthalmology; 2015:183–188.
Rapuano CJ. Phototherapeutic keratectomy: who are the best candidates and how do you treat them? Curr Opin Ophthalmol. 2010;21(4):280–282.
Shah RA, Wilson SE. Use of mitomycin-C for phototherapeutic keratectomy and photorefractive keratectomy surgery. Curr Opin Ophthalmol. 2010;21(4):269–273.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.