Excimer laser phototherapeutic keratectomy before cataract extraction and intraocular lens implantation

Phototherapeutic keratectomy: Indications, methods and decision making

Phototherapeutic keratectomy (PTK) involves treating anterior corneal lesions by superficial corneal ablation using an excimer laser (193 nm). Some of the commonly treated conditions include recurrent corneal erosions (RCE), corneal dystrophies, spheroidal degeneration, keratoconus, and corneal scars. We discuss various techniques of PTK including large area PTK, focal PTK, and multifocal PTK and alternatives to PTK. Masking agents like hyaluronate, methylcellulose, and dextran are recommended to help achieve a better outcome when ablating irregular corneal surfaces. Antifibrotic agents like mitomycin C reduce the chances of recurrence of the disease, apart from minimizing the postoperative scarring. Some of the complications include induced hyperopia and irregular astigmatism, haze, recurrence, and corneal thinning. However, earlier postoperative recovery, possibility of a repeat procedure, and ability to control the depth of ablation make PTK a promising, minimally invasive alternative to keratoplasty in cases with anterior corneal pathologies.

Phototherapeutic keratectomy

Phototherapeutic keratectomy is an excimer laser-based surgical procedure widely performed by corneal surgeons for treating anterior corneal stromal pathologies. Phototherapeutic keratectomy helps by ablating the corneal stroma, thereby improving corneal clarity and smoothening the surface. Transient discomfort and induced hyperopia from corneal flattening are the immediate postoperative concerns. The long-term course is often marked by the recurrence of original corneal pathology and corneal haze formation. Phototherapeutic keratectomy, however, allows for repeat stromal ablation for managing recurrences, as the corneal thickness permits, without affecting the outcome of future keratoplasty. Adjunctive methods such as topical mitomycin-C may be additionally used to reduce recurrence rates. Also, various masking agents such as carboxymethyl cellulose, sodium hyaluronate, and dextran are used in eyes with irregular corneal surface to allow for uniform stromal ablation. Overall, phototherapeutic keratectomy has provided corneal surgeons an additional surgical tool, particularly those residing in developing nations where the availability of donor corneal tissue is an important limiting factor.

Phototherapeutic keratectomy

Phototherapeutic keratectomy (PTK) is done regularly for anterior corneal diseases such as corneal dystrophies, corneal degenerations, scars, and band-shaped keratopathy. The various indications include both therapeutic and visual. The aim of this article is to discuss the therapeutic indications for PTK, the specific technique pertaining to a specific etiology, the various other procedures like amniotic membrane graft combined with PTK or PTK being done for recurrences in the grafts, and PTK done before cataract surgery when the anterior corneal pathology coexists with the cataract. Post PTK management such as healing of an epithelial defect, use of steroids in the post PTK period, recurrences of primary disease pathology, and infections, will be discussed. Methods of literature search: A Medline search was carried out for articles in the English language, with the keywords, phototherapeutic keratectomy, band-shaped keratopathy, spheroidal degeneration, scars, bullous keratopathy, and corneal dystrophy. The relevant references are mentioned here.

Management of band keratopathy with excimer phototherapeutic keratectomy: visual, refractive, and symptomatic outcome

PURPOSE

To report on the outcome of excimer phototherapeutic keratectomy (PTK) in the management of band keratopathy.

METHODS

Analysis was performed on patients undergoing PTK for band keratopathy between January 1996 and December 1999. Patients were assessed as to whether the indication for PTK was for visual rehabilitation (visual group) or for ocular surface improvement (nonvisual group). Further data including pre- and postoperative best-corrected visual acuity, pre- and postoperative spherical equivalent (SE), and associated or previous ocular pathology were collected.

RESULTS

A total of 45 eyes of 33 patients underwent PTK for band keratopathy. In the visual group, there were 33 eyes of 22 patients, and in the nonvisual group 12 eyes of 11 patients. The visual acuity was improved or unchanged in 18/33 eyes (55%) of the visual group, while there was loss of one or more lines of acuity in 15/33 (45%). Loss of acuity was attributed to other factors in 11/15 eyes. There was a significant myopic shift (P<0.5) from the mean preoperative SE of +1.42 D (SD+/-3.21 D) to the mean postoperative SE of +0.32 (SD+/-3.26 D). Of the eyes in the nonvisual group, 10/12 (83%) had significant improvement of symptoms.

CONCLUSION

Excimer PTK is an effective procedure in the management of band keratopathy whether it is performed for visual rehabilitation or for ocular surface improvement to prevent erosions. Concurrent pathology is common and may limit the extent of visual improvement postoperatively. Factors associated with the myopic shift seen in this series may be epithelial remodelling, concurrent ocular pathology, or inaccuracy of preoperative refractive data.

Therapeutic use of the 193-nm excimer laser in corneal pathologies

PURPOSE

To analyze the results of phototherapeutic keratectomy.

PATIENTS AND METHODS

We performed 193-nm excimer laser phototherapeutic keratectomy (PTK) in 252 eyes of 216 patients suffering from pain and/or decrease in visual acuity. One hundred and three eyes had recurrent erosions of the cornea, 86 eyes underwent excimer laser smoothing of the cornea after pterygium surgery, 29 eyes had a bandlike keratopathy (25 rough, 4 smooth) and 34 eyes had other pathologic conditions such as amyloidosis of the cornea, anterior corneal dystrophies, scars after injuries, alkali burns, superficial stromal dystrophies and infections. Recurrent erosions and epithelial dystrophies were treated with 15-20 pulses (160-200 mJ/cm2, 8 mm ablation zone) after mechanical abrasion of the epithelium. Removal of corneal opacities and scars required the use of a masking fluid (methyl-cellulose) in different concentrations and slit-lamp control (integrated in the delivery system of the excimer laser).

RESULTS

Some 91% of the eyes with recurrent erosions were recurrence-free. Fifty-two per cent of the eyes with pterygium had recurrences if the baresclera technique was used and 33% of the eyes if a free conjunctival graft was used. The difference was not significant. All of the patients with bandlike keratopathy were pain-free. In 88% of the eyes with special indications the treatment goal was achieved. No positive effect was seen after alkali burn, in a patient with anterior membrane dystrophy (Grayson-Wilbrandt corneal dystrophy) or in a patient with a corneal protuberance. In one patient with scleroperikeratitis a late recurrence of the opacity was observed 3 years after surgery. A loss of best corrected visual acuity was found only in one patient with bullous keratopathy in whom the treatment goal was the reduction of pain. All patients with smooth bandlike keratopathy had an improvement in best corrected visual acuity of at least one line. About 70% of patients with special indications improved by at least one line, up to nine lines. A possible hyperopic shift in all groups could be minimized using a large ablation zone.

CONCLUSION

PTK with the 193-nm excimer laser is a safe and effective treatment for many superficial diseases of the cornea.