One year follow-up of photoastigmatic keratectomy (PARK) with the VISX 20/20 excimer laser.

BACKGROUND AND OBJECTIVE: One hundred thirteen eyes were treated with photoastigmatic keratectomy using the VISX 20/20 excimer laser. The results were evaluated after 1 year. PATIENTS AND METHODS: The patients were divided into 2 groups, low astigmatism group with less than 2.00 diopters (D) of pre-operative astigmatism, the second group having 2.00 D or more. RESULTS: Astigmatism was reduced by 43.9% in the low astigmatic group and by 71.7% in the high astigmatic group. Eighty percent of the eyes in the low astigmatic group and 90% in the high astigmatic group achieved an uncorrected visual acuity of 20/40 (0.5) or better. Eighty-four percent in the low astigmatic group and 80% in the high astigmatic group were within +/- 1.00 D in spherical equivalent results. The mean spherical equivalent results were about -0.45 D in both groups using this algorithm. CONCLUSION: The results are very promising at this early stage of algorithm development.

Light transmittance of ocular media in living rabbit eyes.

PURPOSE: The purpose of this study was to measure the transmittance of electromagnetic radiation, particularly visible light, through the ocular media of living and whole rabbit eyes. Previous determinations have been carried out on excised cadaver eyes. METHODS: A specially designed fiberoptic probe (outer diameter, 0.9 mm) was placed in the vitreous in front of the retina using a microsurgical technique. In eight living albino rabbits (under general anesthesia), ocular transmittance was determined in the wavelength range 350 to 1100 nm using a reversed beam path (from vitreous to cornea). RESULTS: A maximum optical transmittance of 94% to 96% (standard deviation, 2%-3%) was found between 630 and 730 nm (reflection losses in the cornea-air interface excluded). In the blue portion of the spectrum, transmittance decreased rapidly for shorter wavelengths, and was 50% at 400 nm and less than 1% at 380 nm. In the infrared part of the spectrum, transmittance was close to 90% up to 900 nm but declined at longer wavelengths, coinciding with the absorption in pure water. Calibration recordings showed a 1% to 2% accuracy of the method. CONCLUSIONS: This experimental technique using an intraocular fiberoptic probe yields a high accuracy and indicates that light transmittance is very high in vivo and superior to that reported from cadaver eyes.

Inactivation of lactate dehydrogenase by UV radiation in the 300 nm wavelength region.

The effect of UV radiation on lactate dehydrogenase (LDH) was investigated. LDH from bovine heart was exposed to 3.6-18 kJ/m2 of ultraviolet (UV) radiation in the 300 nm wavelength region. The activity of LDH was observed to decrease as a function of the dosage of UV radiation. The inactivation of LDH was independent of exposure rate at constant dosage of UV radiation. The decrease of LDH activity caused by UV 300 nm radiation was coupled to a decrease of the maximal velocity (Vmax) while the Michaelis constant (Km) remained unchanged. The absorption spectrum of the LDH changed during exposure to UV radiation suggesting an alteration of tryptophan in the LDH molecule.