Diabetes and corneal cell densities in humans by in vivo confocal microscopy.

PURPOSE: Diabetes is accompanied by an increased autofluorescence of the cornea, probably because of accumulation of advanced glycation end products (AGEs). The pathogenic mechanism is still unknown. This study aimed to quantify differences in corneal cell densities between diabetic patients and healthy controls. METHODS: The left cornea of 15 patients with non-insulin-dependent diabetes mellitus (NIDDM) with level of retinopathy 20 according to the Early Treatment of Diabetic Retinopathy Study (ETDRS) and of 15 healthy controls were examined by noninvasive in vivo confocal microscopy in an observational prospective study. The cell densities in 6 corneal layers were determined along the optical axis of the cornea by using stereologic methods. RESULTS: The average cell density per unit area in the superficial and basal epithelium and the endothelial layer was 725 +/- 171, 5950 +/- 653, and 2690 +/- 302 cells/mm in controls and 815 +/- 260, 5060 +/- 301, and 2660 +/- 364 cells/mm in diabetic patients. The cell density per unit volume in the anterior, mid-, and posterior stroma was 26,300 +/- 4090, 19,390 +/- 3120, and 25,700 +/- 3260 cells/mm in controls and 27,560 +/- 3880, 21,930 +/- 2110, and 25,790 +/- 3090 cells/mm in patients with diabetes. In both groups, the density in the midstroma was significantly lower than in both the anterior stroma and the posterior stroma (P < 0.02). The cell density in the basal layer of diabetic patients was significantly lower than in healthy controls (-15.0%, P < 0.0004). In the other layers, no significant differences between both groups (P > 0.07) were observed. CONCLUSIONS: The lower basal cell density found in patients with diabetes may result from a combination of different mechanisms including decreased innervation at the subbasal nerve plexus, basement membrane alterations, and higher turnover rate in basal epithelial cells. The lower cell density in the midstroma of diabetic patients and healthy controls may be attributed in part to differences in oxygen concentration in the stromal layers (depths). Changes in cellular density did not seem to be responsible for the increased autofluorescence in diabetes.

Corneal cell density measurement in vivo by scanning slit confocal microscopy: method and validation.

PURPOSE: Method and validation of a technique to quantify cell density in vivo in 6 corneal layers with a scanning slit confocal microscope (SSCM). METHOD: A confocal image of a small volume in a corneal layer is registered on videotape. Cells or nuclei according to a layer classification are counted manually using an unbiased frame. Surface cell density is calculated from an image on the screen, and volumetric density is obtained using stereological methods. RESULTS: Image distortion on the screen is less than 3%. The classification of a cell layer is verified by determining the position of the measurement volume in the cornea. Validation of density measurements is performed by comparing confocal results with those obtained by histology. The difference between the two methods varies from -24.1% (posterior stroma) to +16.4% (basal layer). Intersession and intrasession repeatability are 8.3 and 5.8%, respectively. The cell density (mean +/- SD) in 20 healthy controls in the superficial, basal and endothelial layers was 759 +/- 162, 5,817 +/- 632 and 2,743 +/- 285 cells.mm(-2) (surface), and in the anterior, mid and posterior stroma 28,616 +/- 3,081, 19,578 +/- 4,421 and 26,073 +/- 5,962 cells.mm(-3) (volumetric). These results are in accordance with those of other investigators. CONCLUSIONS: The SSCM can produce repeatable quantitative measurements of corneal cell density in conscious humans.

[Results of scanning and flying spot technologies in photorefractive keratectomy (PRK) for hypermetropia]. / A pásztázó- és repülópont-technikával végzett fotorefraktív keratectomia eredményei hypermetropiában.

AIM OF THE STUDY: To compare the results of scanning and flying spot laser beam technologies of photorefractive keratectomy (PRK) in eyes with hypermetropic refractive error. PATIENTS AND METHODS: In Group I (n = 800) eyes were treated with scanning technology (Aesculap-Meditec MEL 60), in Subgroup I/1 (n = 482) those eyes, which had a preoperative refractive error between +1.0 and +3.5 D; in Subgroup I/2 (n = 318) the eyes between +3.75 and +6.5 D. In Group II (n = 200) eyes treated with flying spot technology (Aesculap-Meditec MEL 70 G-Scan) were evaluated; in Subgroup II/1 (n = 106) eyes between +1.0 and +3.5 D; in subgroup II/2 (n = 94) eyes between +3.75 and +7.5 D. Follow-up time was 12 months. RESULTS: The preoperative correction need decreased in Group I/1 from +2.88 +/- 1.34 D to +1.26 +/- 1.24 D; in Group I/2 from 64 +/- 2.96 D to +2.46 +/- 1.84 D; in Group II/1 from +2.94 +/- 1.42 D to +0.42 +/- 0.14 D and in Group II/2 from 48 +/- 2.62 D to +0.86 +/- 0.6 D 12 months after PRK. Postoperative uncorrected visual acuity (UCVA) was 1.0 or better in 75.7% within the eyes of Group I/1; it was 22.3% in Group I/2; 80% in Group II/1 and 64.8% in Group II/2. The percentage of the eyes within +/- 1.0 D of targeted refraction was: In Group I/1 86.1%, in Group I/2 45.3%, in Group II/1 92.4% and in Group II/2 78.7%. The best spectacle-corrected visual acuity (BSCVA) decreased by 2 or more Snellen lines among the eyes of Group I/1 in 12%; in Group I/2 in 21%; in Group II/1 in 2.8% and in Group II/2 in 9.6%. In Group I/1 2%, in Group II/1 3.8% of the treated eyes gained 2 or more lines of BSCVA. Among the eyes treated with the scanning model (Group I/2) a central bump-like opacity was observed in 4 eyes (1.2%); among the eyes treated with the flying spot model no similar complication occurred. The postoperative increase of intraocular pressure was observed in 7.5% in Group I/1; in 6.8% in Group I/2; in 7.0% in Group II/1; and in 6.4% in Group II/2. CONCLUSIONS: Flying spot technology was superior to scanning method in each treatment group, difference was greatest in eyes treated with a preoperative refractive error higher than +3.75 D. The upper limit of hypermetropic treatments has increased to +6.0 D in case of flying spot treatments from the previous +3.5 D upper limit of scanning technology.

Photorefractive keratectomy using the meditec MEL 70 G-scan laser for hyperopia and hyperopic astigmatism.

PURPOSE: To evaluate the results of photorefractive keratectomy (PRK) using Gaussian flying spot technology in the treatment of hyperopia and hyperopic astigmatism. METHODS: Two hundred eyes were evaluated with 12-month follow-up. An Asclepion-Meditec MEL 70 G-scan flying spot ArF excimer laser with a Gaussian scanner was used (6.0-mm treatment zone and 9.0-mm transition zone). Eyes were divided into four groups: Group 1 (spherical hyperopia up to +3.50 D and astigmatism less than 1.00 D, n=62); Group 2 (hyperopia up to +3.50 D and astigmatism of 1.00 D or more, n=44); Group 3 (hyperopia greater than +3.50 D and astigmatism less than 1.00 D, n=56); and Group 4 (hyperopia greater than +3.50 D and astigmatism of 1.00 D or more, n=38). RESULTS: In Group 1, 82.2% (51/62 eyes) were within +/-0.50 D of target refraction; 88.7% (55/62 eyes) had 20/20 or better uncorrected visual acuity; 1.6% (1/62 eye) lost two or more lines, 3.2% (2/62 eyes) gained two or more lines of spectacle-corrected visual acuity. In Group 2, 68.1% (30/44 eyes) were within +/-0.50 D; 77.2% (34/44 eyes) had 20/20 or better uncorrected visual acuity; 9.1% (4/44 eyes) lost two or more lines of spectacle-corrected visual acuity. In Group 3, 76.8% (43/56 eyes) were within +/-0.50 D; 78.6% (44/56 eyes) had 20/20 or better uncorrected visual acuity; 5.4% (3/56 eyes) lost two or more lines of spectacle-corrected visual acuity. In Group 4, 42% (16/38 eyes) were within +/-0.50 D; 60.5% (23/38 eyes) had 20/20 or better uncorrected visual acuity; 15.8% (6/38 eyes) lost two or more Snellen lines. CONCLUSION: PRK with the flying spot Meditec MEL 70 G-scan was most safe and effective for low hyperopia.