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.

[Special indications for photorefractive (PRK) and phototherapeutic (PTK) excimer laser keratotomies. A presentation of 5 cases]

Five patients with specific indications for photorefractive and phototherapeutic keratectomy (PRK and PTK) by excimer laser at 193 nm were treated successfully: they had presented with epithelial dystrophy of the cornea, amyloid, von Szilly's scleroperikartitis, myopia after cataract extraction and before secondary implantation of an intraocular lens in the other eye, and myopia. In all cases it was possible to avoid extensive surgical procedures such as lamellar keratoplasty or intraocular lens exchange. There were no recurrences in the patients with superficial corneal diseases, and the patients who had undergone PRK were within 0.25 Dpt of the target acuity. The follow-up was between 8 months and 1 year.

[Excimer laser phototherapeutic keratectomy (PTK) and modified bare sclera technique for treatment of pterygium]

Forty-six pterygia were surgically removed using a modified "bare sclera" technique. Additionally, an excimer laser PTK was performed using the immersion method to smooth the irregular surface of the cornea. Follow-up was 6 to 10 months. We found 24 recurrences. In patients with pterygia of more than 4 mm who were from southern Europe, the Middle East, or Africa, the recurrence rate was 100%. In pterygia from 2 to 4 mm the recurrence rate was 50%; in pterygia up to the limbus no recurrences were noted. The excimer laser has no positive influence on pterygia recurrences that have been removed using the modified "bare sclera" technique.

[15 months photorefractive keratectomy at the Munster University Eye Clinic]

We performed a photorefractive keratectomy (PRK) in 51 myopic eyes of 34 patients. Cortisone-responders were excluded. All patients were unable to tolerate contact lenses. The intended correction was between -1.75 and -7.0 D. None of the patients demonstrated a decrease in visual acuity at its highest level of correction. The maximum haze was +1. No eye had to be reoperated upon. Nine months after PRK, the maximum deviation from the intended correction was 2 D in a -6.5 D correction. After 12 months, however, we found a regression of 2 D without signs of keratoconus or increase of haze in 2 patients.

Phototherapeutic keratectomy in corneal diseases

We present our clinical strategy to treat corneal diseases with the excimer laser. Nine eyes with recurrent erosion after trauma, three eyes with band keratopathy, and one eye with secondary crystalline deposits and a leukoma adherens after perforating injury underwent excimer laser phototherapeutic keratectomy (PTK). The patients with recurrent erosion had at least six episodes in the 12 months, the other patients suffered from severe pain. The recurrent erosions were treated with 15 pulses (193 nm, 180 mJ/cm2, 10 Hz) after removing the epithelium. There was only one new episode within 6 months after treatment in a patient who failed to follow the postoperative therapeutic regimen. In the patients with band keratopathy we removed the calcium deposits mechanically and then used masking fluids to obtain a smooth surface. The crystalline deposits in the patient with leukoma adherens could be removed but recurred after 4 months; the patient still suffered from glare.