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The key to a successful outcome depends on proper case selection. Systemic diseases such as uncontrolled diabetes, collagen vascular diseases like rheumatoid arthritis, and systemic lupus erythromatosus may have delayed epithelial healing. Corneal diseases limited to anterior stroma are amenable to treatment. Mitomycin C (MMC) is used as an adjunctive treatment to prevent recurrences. Most common PTK conditions treated include:
Recurrent Corneal Erosions
Anterior Corneal Scars
We do PTK for both visual and therapeutic reasons. Visual improvement after PTK is due to reduced density or removal of a scar and reduced irregular astigmatism. There may be a reduction in UCVA due to induced refractive errors, but the best corrected visual acuity (BCVA) improves. The clear cornea may help in accurate keratometry for intraocular lens (IOL) power calculation. PTK improves symptoms of pain, watering, and foreign body sensation in RCE, in dystrophies, bullous keratopathy, and spheroidal degeneration.
Corneal diseases limited to anterior stroma are amenable to treatment. Salzmann nodular degeneration (SND) is characterized by the presence of bluish-white peripheral nodules raised above the corneal surface, slowly progressive, more common in females with longstanding scars and chronic uveitis. The raised surface may be associated with tear film abnormality, irregular astigmatism, and difficulty in contact lens fitting. Surgery is the only treatment.
Bullous keratopathy is characterized by bullae formation and its rupture, resulting in symptoms of pain, foreign body sensation, watering. The treatment is two-fold symptomatic relief and visual improvement. The first goal of symptomatic relief is with hyperosmotic agents, bandage contact lens (BCL) or with anterior stromal puncture (ASP), AMG, PTK, ASP with AMG, and PTK with AMG. The second goal is visual improvement. PTK is a very promising and effective treatment for bullous keratopathy and can also be repeated
Phototherapeutic keratectomy is indicated for anterior basement membrane dystrophies (ABMD) and stromal dystrophies for both symptomatic relief and visual.
improvement. Dystrophies being central, the ablation profile of PTK mimics myopic correction and thereby induces hyperopia. This depends on the amount of ablation depth. Also, intraoperative application of MMC helps prevent recurrences. PTK works well for recurrent epithelial breakdown or recurrent epithelial erosions. This occurs when the epithelial attachments to the underlying stroma are loose and eventually break.
Superficial anterior stromal avascular scars (less than 100 microns), are amenable to treatment by PTK. These scars may be post-traumatic, post-infectious or post-pterygium excision. The aim is to improve vision and delay or obviate the need for keratoplasty. Scars after healed bacterial or fungal keratitis can be treated with PTK.
The technique of PTK varies according to the underlying pathology, size, and site. Hence, it is better explained as a common method first and then the specific technique in the specified pathology can be modified as described. The procedure is generally done under topical anesthesia, unless some additional surgical procedure is combined with PTK. The procedure is done under strict aseptic precautions. After applying the wire speculum, the epithelium is debrided manually with a hockey stick knife. The epithelium comes out easily in bullous keratopathy. Some surgeons do use alcohol for the debridement of the epithelium. After debriding the epithelium, ablation is performed either by asking the patient to look into the fixation light or a laser is centered manually. A few visual and auditory signals during the procedure may help in guiding the extent of the treatment. A snapping sound is heard when the tissue is ablated. Usual treatments last 15-90 seconds.
The immediate post-operative care of PTK is concentrated on healing the epithelial defect. We monitor the bandage contact lens fit and typically don’t remove it until we are sure there is no epithelial defect. A bandage contact lens that is too tight can cause more discomfort to the patient, while a loose contact lens can make it more difficult for the epithelium to heal.
Prednisolone acetate 1%:1 drop QID for one week, then 1 drop BID for 1 week.
Vigamox/4thgeneration fluoroquinolone:1 drop 6 times per day while contact lens is in (typically 4 days). Then use it QID for 3 days.
Acuvail: as needed for pain with a maximum of BID for 3 days. DO NOT use for more than 3 days.
The patient is given a prescription for a narcotic pain reliever (to use for pain) and cold compresses are encouraged especially on the temporal region. These can help for those patients with more discomfort. The patient is evaluated at one day to assess vision and monitor epithelial healing. Patients are warned that vision may take a few steps backward over the next several days as the epithelium moves centrally and crosses over the pupil. A smooth epithelial-leading edge should be noted under the contact lens, and epithelial growth of up to 20% can be seen at one day. The patient is re-instructed on the drop regimen and is scheduled to be seen 3 days later. At the four day appointment, the epithelium should be intact or at least very close. If a fairly large, greater than 2 mm epithelial defect is present at 4 days, suspect a slowing of epithelial growth.
If a delay in epithelial growth is suspected we recommend reducing the steroid and discontinuing NSAID use, continue the bandage contact lens, increase lubrication and follow daily. Refrain from discontinuing the steroid completely in order to minimize the chance of a sterile infiltrate. The combination drop (Pred/Moxi) can be reduced to BID to decrease steroid use, but our preference would be to switch the patient to two drops, a fluoroquinolone (Vigamox) and Prednisolone Acetate, so steroid use can be controlled but not sacrificing antibiotic use.
Protocol for Delay Epithelial Closure:
Reduce Steroid: Pred. Acetate 1% BID
Continue Antibiotic: Vigamox 6x/day
Inferior and Superior punctal occlusion
Thicker AT, Celluvisc, Liquigel, etc. q 2 hr
Night time gel or ointment
Monitor Daily until re-epithelialized
**If not re-epithelialized by 6 days call to schedule to be evaluated in our center
Typically, the epithelium will seal with a small centrally located epithelial ridge. It can be star shaped or linear, will usually pick up stain and depending on where the ridge is located, it can have varied effects on vision. Once re-epithelialization has occurred, the bandage contact lens is removed. The use of consistent daily and night-time lubrication will help promote continued epithelial healing and adherence, as well as aiding in the epithelial remodeling that occurs following PRK. It is this epithelial remodeling that will continue to improve the patient’s vision with time.