[Femtosecond laser: a micromachining system for corneal surgery]. / Laser femtoseconde: système de micro-usinage pour chirurgie de la cornée.

INTRODUCTION: The authors present the diode-pumped, all-solid state, neodymium:glass femtosecond laser from the Laboratory of Ocular Biotechnology, Hotel-Dieu Hospital. MATERIALS AND METHODS: We worked with a 1,065-nm wavelength infrared laser. This laser is composed of an oscillator and amplification glass matrix mixed with neodymium. Its stretching and compression system is capable of producing pulses lasting a few hundred femtoseconds. The repetition rate is adjustable, ranging from 1 to 10 kHz, and can reach energies up to 60 microJ. The delivery system was set up on an optical table, with human corneal samples fixed to an anterior chamber system, which can be moved over the X-Y-Z axis by a computer-guided translation motor with micrometric precision. We analyzed the biological effects of laser impacts in human corneal tissue, obtained from the French Eye Bank. RESULTS: The femtosecond laser provides automated corneal cutting with a high level of precision, which can be verified on the corneal surface regularity by scanning electron microscopy analysis. Silicon samples can also be cut and can be used for calibration testing of the laser. CONCLUSION: The set-up composed of the femtosecond laser and the described delivery system enable precise corneal cutting and offer the opportunity to study its characteristics.

Gaussian optics for photorefractive keratectomy. Increased predictability for larger diopter corrections.

PURPOSE: To evaluate clinically a formula based on spherical Gaussian optics for enhanced predictability of excimer photorefractive keratectomy (PRK) in both high and low degrees of myopia. METHOD: Patients (24 eyes) were evaluated preoperatively with refractive measurements and corneal topography. After excimer PRK (3-24 months), postoperative remaining spectacle correction and corneal topography were measured. The attempted laser correction, calculated using algebraic equations, was compared with the achieved laser correction. RESULTS: The absolute laser correction error (mean +/- standard deviation), defined as the difference between the achieved and attempted laser corrections, was 0.37 +/- 0.31 diopter (D) for the 24 eyes. No significant difference was found in the error for attempted corrections greater than 6 D versus those less than 6 D. CONCLUSION: The use of a spherical Gaussian optics formulation results in accurate laser correction values for a wide range of myopia, even for large diopter corrections.

Photorefractive keratectomy for the correction of myopia and astigmatism.

Photorefractive keratectomy corrects myopia with or without astigmatism by decreasing the refractive power of the central cornea. The Colliac matrix formula determines the anterior corneal radius of curvature expected to achieve emmetropia. We used the formula as an algorithm for the computer-controlled delivery of the laser beam. The formula was evaluated by using theoretical and clinical cases. We examined the relationship between the correction induced by photorefractive keratectomy, the diameter of ablation zone, and the thickness of the ablated corneal lenticule on the optical axis. Comparison between attempted and achieved keratometric readings showed the accuracy of the formula to be in the order of +/- 0.75 diopter.

Optics for photorefractive keratectomy.

Matrix calculations are applied to Gaussian optics in the study of myopic correction by photorefractive keratectomy. The Colliac matrix formula determines the postoperative anterior curvature radius of the treated cornea. It also calculates the maximal depth of the removed corneal tissue and the ablation zone diameter needed to achieve emmetropia.

[Ultrasonic treatment of hypertonia caused by intraocular silicone oil]. / Traitement par ultra-sons des hypertonies provoquées par l'huile de silicone intra-oculaire.

The authors treated 53 patients with uncontrolled glaucoma in silicone oil filled eyes with high intensity focused ultrasound. The silicone oil filled eyes present unusually difficult problems in glaucoma management, since the silicone oil rapidly obstructs filtration openings, and laser techniques have not been effective. The mean pretreatment pressure was 34.2 mmHg. The patients were followed for a mean of 17 months. Seventy-five per cent of ultrasound treated eyes had successful reduction of intraocular pressure to below 20 mmHg with or without concomitant medical treatment at two years after treatment. The complication rate was low in this group of eyes. Five eyes developed hypotonia and three eyes had full thickness scleral perforations but were effectively controlled and developed no other complications during two years of follow-up. This technique appears more effective than cyclo-destructive techniques alone.

[Indications and results of Sonocare (ultrasound) in the treatment of ocular hypertension. A preliminary study of 395 cases]. / Indications et résultats du Sonocare (ultrasons) dans le traitement des hypertonies oculaires. Etude préliminaire sur 395 cas.

The Sonocare system CST 100 provides high-intensity focused ultrasound to lower the intraocular pressure by three different mechanisms: partial destruction of the ciliary epithelium, scleral thinning allowing transcleral outflow of aqueous humor, and mainly the ciliary body separation from the sclera. Initially it was used to treat blind eyes with painful elevated intraocular pressure; now the indications are gradually extended to eyes with good vision. This technique takes place between laser trabeculoplasty and filtering surgery. The first 395 cases which were treated with ultrasound these two last years in the Quinze-Vingts Hospital, are displayed in this report.

Matrix formula for intraocular lens power calculation.

The matrix calculation was applied to Gaussian optics. Matrices were defined for a single diopter, a lens, an association of two centered systems having the same axis when the origins are taken at the vertices of the first and last refracting surfaces. The matrix formula then was used to calculate the power of the emmetropizing lens implant, and its results compared with the ones obtained by five other formulas.

Twenty-five cases of relaxing retinotomy using a nanosecond Nd Yag laser (Yag-retinotomy).

The results of the first 25 retinotomies performed with a nanosecond Nd Yag Laser (Nanolas, Biophysic Medical) between September 1986 and July 1987 are described. This technique was chosen in order to avoid additional surgery and anesthesia in patients requiring a relaxing retinotomy. Treated eyes were usually filled with silicone oil. Simple contact anesthesia and a three-mirror lens were sufficient. Energy was set at 10-15 mJ, 50 Hz burst mode, 10 degrees cone angle. The aim of the treatment was to eliminate a residual inferior traction, to remove silicone oil (19 cases), or to obtain reapplication at the posterior pole. Results were positive in 18 cases and negative in 7, but unsuccessful Nd Yag laser treatment may be corrected with surgical retinotomy. The main complication is hemorrhage, which usually subsequently decreases and does not affect the prognosis.