The problems of using UV excimer lasers generating ...

JOURNAL DE PHYSIQUE IV Colloque 0, supplkment au Journal de Physique 111, Vol. 1, dkembre 1991

CLINICAL APPLICATION OF UV EXCIMER LASERS

V.V. LANTUKH, M.M. PYATIN and A.M. RAZHEV "EyeMicrosurgery" R. & T Complex, NovosibirskAfiliated Branch, 10 Xolkhidskaya St., Novosibirsk 630071, USSR Institute of Laser Physics, SSibehn Branch of the USSRAcademy of Sciences, 1313 Lavrenvev fi,Novosibirsk 630090, USSR

Abstract - The problems of using U V excimer lasers generating at the z3 and 248 nm wavelengths in the treatment of myopia, a p h a k i a ~ g ~ i a ~ c oand m a Herpes Simplex keratitis is discussed. The results of clinical application of these excimer lasers are presented.

The scope of laser surgery used in eye disorders is widening from year to year. Lately, the use of excimer lasers emitting U V radiation has been attracting great interest. To the well-known advantages of laser surgery (sterility and no-touch technique) another important feature the ability to produce incisions of controlled shape and is added depth with submicron precision and without any damage to the adjacent tissues. A number of workers proved it experimentally 1 1 - 5 1 . The mutagenic effect of U V laser - corneal tissues (bone marrow cells) interaction was studied. The number of possible laser-induced chromosome oberrations was shown to be not higher than that of spontaneous mutations L7 1 The positive results obtained made it possible t o use excimer lasers for t h e treatment of certain eye disorders.

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Materials and methods. A specially designed pulsed excimer laser with a short pulse scheme generating effectively at all transitions of rare gas halides wit! t h e energy of several dozen mJ per pulse the duration of which is 4.5-0.5 ns was used [8] The laser is physically and optically coupled with the operating microscope by means of a delivery system making it possible t o project a focal plane onto the cornea.

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Treatment of Herpes Simplex keratitis. 122 patients with a severe or torpid form of the disease underwent laser treatment. In this group 110 patients had epithelial dendri form keratitis, 8 patients had epithelial ulcerative keratitis and 4 patients had deep stromal keratitis. Prior to laser treatment epibulbar anesthesia was used. The affected area o f t h e cornea was determined by instillation of fluorescein.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:1991757

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JOURNAL DE PHYSIQUE IV

A helium neon laser was used t o enable t h e surgeon t o define t h e focal plane of t h e beam on t h e cornea. Photoablation of t h e corneal epithelium, necrotized tissues and infiltrated was carried out with t h e e x cimer laser. The operating microscope was used t o control t h e depth and t h e area of t h e ablated zone. Low energies of radiation (0.4-0.5 m J ) were used. The KrF excimer laser generated at t h e wavelength of 2 4 8 nm. During t h e exposure t h e diameter of t h e focal spot could be changed depending on t h e area of t h e lesion. No antiviral preparations w e r e used postoperatively. The findings of t h e follow-up examination showed t h e 2 4 8 nm wavelength t o be t h e most effective in t h e laser treatment o f Herpes dendriform keratitis. In t h i s group of patients recovery and epithelialization w e r e observed by t h e 4th postoperative day. If more than o n e third of the cornea was affected, epithelializat i o n and recovery w e r e noted by t h e 8th-10th day postoperatively. In patients with stromal keratitis t h e recovery process lasted 2-3 weeks. In all groups of patients t h e r e were no recurrences-. Treatment of Refraction Errors. T h e excimer laser gives a unique possibility of changing t h e curvature of t h e anterior surface o f t h e cornea and thereby changing its refractive power. T h e study group consisted of 2 4 patients with myopic anisometropia and 2 patients with posttraumatic aphakia, synechial cicatrices and an2 irregular pupil. T o perform laser surgery in t h e latter c a s e s a special rotating aperture was designed which produced a beam of energy distributed from t h e c e n t e r towards t h e periphery. Thus, a positive meniscus of t h e cornea was formed. T o obtain t h i s result t h e curvature radius o f t h e central cornea had t o be 6 mm. Following t h e healing of t h e ablated z o n e t h e second stage of t h e operation w a s performed - reconstruction of t h e iris and t h e vitreous. T o correct myopia of high degree a rotating mask was used t o produce a beam with t h e maximum energy in t h e center t o form a negative meniscus. Twenty patients had laser treatment without Bowman's membrane being separated. In 4 patients t h e superficial layer of t h e cornea was removed. The bed was 150pm deep, its area being 5 mm. The depth of t h e ablated z o n e depth in t h e central cornea depended on t h e preoperative refraction and corneal thickness and w a s equal t o 30-50ym. In 4 pat i e n t s t h e separated corneal f l a p w a s positioned in its original place and fixed with t h e biologic glue. Analysing t h e clinical findings obtained one can say t h a t t h e use of 193 nm radiation gives g o o d r v i s u a l results; t h e r e is practically no haze and t h e degree of astigmatism did not exceed t h e physiologic norm. With t h e use of 2 4 8 nm radiation t h e clinical outcomes w e r e worse especially in t h e immediate post-operative period on account of t h e superficial haze o f t h e bed floor. But in t h e follow-up period (more t h a n I y e a r ) t h e r e w e r e no signs of t h e haze. T h e most effective t e c h nique of preparing t h e cornea f o r laser treatment was a very thorough and careful removal o f t h e superficial epithelium. Treatment o f open-angle glaucoma. The excimer laser w a s used t o treat 16 patients with open-angle glaucoma. The surgical technique w a s deep sclerectomy (perforating and nonperforating). After separating conjunctival and scleral f l a p s t h e z o n e of Schlemm's canal was opened and its outer wall lamellae w e r e removed with t h e laser radiation in t h e form of a focal spot of 1 mm d i a m e t e ~ , with t h e radiation energy of 5 mJ and energy density up t o 8 0 0 mJ/cm

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If filtration was established after this procedure, t h e operation was finished. In pronounced trabecular sclerosis laser ablation of the inner wall of the S c h l e m m l s canal was used, and laser basal iridectomy was performed. The scleral and conjunctival flaps were sutured on. The findings of short-term and long-term follow-up showed stable normalization of intraocular pressure in all the patients. In one patient who had undergone non-perforating sclerectomy instillations of miotics were necessary. Thus, the excimer laser can be considered a useful ophthalmic tool in t h e treatment of certain eye disorders. The 193 nrn excimer laser is more effective in refractive corneal surgery, whereas the 248 laser proved to be useful in the laser treatment of Herpes Simplex keratitis. Good clinical outcomes in patients with open-angle glaucoma depend on the type of the surgical technique used and on the laser output power.

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