Biomedical subjects

D S Gartry

Publications and source records attributed to D S Gartry.

21 records · Page 2Linked to original sources

PubMedDate not supplied

Corneal light scattering after excimer laser photorefractive keratectomy: the objective measurements of haze.

BACKGROUND: After photorefractive keratectomy using excimer lasers (193 nm), most corneas show a marginal loss of transparency (haze) and the assessment of its magnitude in clinical studies has been subjective. To address this problem, we have developed a new device for the objective measurement of haze by measuring corneal light scattering. METHODS: A CCD-camera was fixed at 40 degrees to a slit-lamp microscope and connected via frame-grabber to a computer. By incorporating polarizing filters, the system could discriminate between reflected and scattered light. The intensity of light coming from the cornea was measured in gray scale levels using in-house image analysis software. The system was calibrated against three different sizes of microspheres (0.25, 0.50, and 5.00 microns) which corresponded to the size of cellular and extracellular elements known to occur at sites of corneal surgery. Data were obtained from three treated human eyes with measurements before treatment and at five different postoperative intervals with a maximum follow up of 4 months. RESULTS: All three sizes of microspheres caused disturbances in gray scale levels (36 to 255 units) in the same range of those observed in corneal measurements. Disturbances in corneal light scattering were noted from 1 week postoperatively and persisted throughout the period of observation. We observed an increase in reflected and scattered light until the 2nd postoperative month followed by a subsequent decline. CONCLUSIONS: It appears that this device is very useful to defect and measure objectively disturbances in corneal transparency after excimer laser photorefractive keratectomy.

Adult↗

PubMedDate not supplied

Photorefractive keratectomy with an argon fluoride excimer laser: a clinical study.

The results of excimer laser photorefractive keratectomy (PRK) in 16 blind and 120 sighted eyes (136 patients) are presented. Follow up for the blind eyes was 22 months and for the sighted eyes 8 to 18 months (mean, 1 year). A Summit Technology UV200 excimer laser with fluence fixed at 180 mJ/cm2, beam diameter 4 mm, a frequency of 10 Hz, and ablation rate of 0.22 mu per pulse was used. The range of preoperative myopia was - 1.50 diopters to - 17.50 D (spherical equivalent). Ninety percent of patients undergoing a -2.00 D correction and 75% of patients undergoing a -3.00-diopter correction were within +/- 1.00 D of intended refraction at 6 months. This figure fell to 40% and 20% for the groups undergoing -6.00 D and -7.00 D corrections, respectively. While the trend is toward undercorrection, around 70% of patients in all groups have benefited from a reduction of their myopia by at least half that intended. A variable degree of anterior stromal "haze" was detected in 110 patients (92%) despite a rigid high dose topical corticosteroid regime over 3 months. Best spectacle corrected visual acuity, however, was greater than or equal to preoperative levels in 111 patients (93%). Six patients experienced a reduction of one line of Snellen acuity at 6 months and three of the high myopes lost two lines. No patients lost more than two lines of Snellen acuity. Ninety-four patients (78%) noticed a "halo" around lights at night, more marked in the early postoperative period, which we attribute to the 4-millimeter diameter ablation zone. With a large pupil, both central and paracentral cornea can contribute simultaneously to the retinal image. We have demonstrated considerable individual variation in response to this surgery, which is more marked in high myopia. Although follow up at the present time is limited, to date PRK appears to be a safe procedure that holds considerable promise for refractive surgery in the future.

Blindness↗

PubMedDate not supplied

Excimer laser photorefractive keratectomy for myopia: comparison of 4.00- and 5.00-millimeter ablation zones.

BACKGROUND: To date, there has been no systematic study of the effects of ablation zone diameter on the outcome of photorefractive keratectomy. To address these issues, we examined a series of eyes with bilateral corrections using different-sized ablation zones. METHODS: Thirty-three patients underwent bilateral photorefractive keratectomy (Summit Excimed UV200, Waltham, Mass) with identical dioptric corrections in both eyes, except first eyes had 4.00-millimeter and second eyes had 5.00-millimeter ablation zones. Identical postoperative eyedrop regimens were used in both eyes of each subject and the interval between treatments was 12 months. The mean depth of the programmed central ablation was 24 microns in eyes treated with 4.00-millimeter and 39 microns with 5.00-millimeter zones. RESULTS: There was no statistically significant difference in the preoperative refraction between first and second eyes. Mean changes in refraction at 1, 3, 6, 9, and 12 months were significantly greater in eyes treated with 5.00-millimeter ablation diameters (p < .001). No eyes treated with 4.00-millimeter zones were overcorrected, but five eyes (15%) treated with 5.00-millimeter beams had a refraction greater than +1.00 diopter (D) at 12 months postoperatively. There was no significant difference in the amount of anterior stromal haze between the two eyes at any stage. In 14 patients, less night halo was noticed in the eye treated with a 5.00-millimeter zone. Using a computer program, halo measurements were made in both eyes of 12 patients whose pre- and postoperative refractions were within 0.50 D. The magnitude of halo was significantly less in eyes treated with 5.00-millimeter zones (p < .01). CONCLUSIONS: Despite greater depths of stromal ablation with 5.00-millimeter diameters, there was no increased anterior stromal haze or postoperative regression of refraction. The biological and physical constraints governing the optimum size of the photorefractive keratectomy ablation zone are discussed.

Adult↗