[Show abstract][Hide abstract] ABSTRACT: To develop an objective and repeatable method of measuring corneal backscattered light from different depths of the cornea in vivo.
A modified slit lamp ("scatterometer"), with a video camera and synchronous white strobe light, was used to capture images of a 0.1-mm-wide slit beam through the cornea. Image analysis software was developed to measure backscatter from digitized high-magnification images of 82 normal corneas of 41 subjects. Forty eyes of 20 of the same subjects were examined again after 1 month. Mean backscatter from the anterior, middle, and posterior thirds of the cornea was compared between repeated measurements, and expressed in arbitrary scatter units (SU).
Backscatter in the anterior third of the cornea was 451 +/- 42 SU (mean +/- SD, n = 82), from the middle third was 274 +/- 29 SU (n = 82), and from the posterior third was 242 +/- 28 SU (n = 82). The difference in backscatter measured a month apart was 5 +/- 27 SU (P = 0.34), 2 +/- 17 SU (P = 0.42), and 0 +/- 15 SU (P = 0.95) in the anterior, middle, and posterior thirds of the cornea, respectively. Minimum detectable differences between measurements were 12, 8, and 7 SU in the anterior, middle and posterior thirds, respectively (alpha = 0.05, beta = 0.20, n = 40).
Backscatter can be measured at different depths of the cornea from high-magnification digitized images of a narrow slit beam through the cornea. The method is objective and repeatable and can be applied in prospective studies of deep and posterior lamellar keratoplasty.
[Show abstract][Hide abstract] ABSTRACT: To compare subbasal corneal nerve and keratocyte density and endothelial characteristics of ocular hypertensive patients treated with medications or observation.
Participants in the Ocular Hypertensive Treatment Study (OHTS) randomized at Mayo Clinic to medication or observation were evaluated with specular microscopy annually for 6 years. Confocal microscopy was performed 78 to 108 months after enrollment. Subbasal nerve density was calculated by manual tracing and digital image analysis. Keratocyte density was determined by manual counting methods. Data were compared using a t test and a rank sum test.
After 6 years, corneal endothelial cell density, percent hexagonal cells, and coefficient of variation of cell area for the observation (n = 21) and medication groups (n = 26) were similar (2415 +/- 300 vs. 2331 +/- 239 cells/mm; 63% +/- 11% vs. 65% +/- 10%; and 0.32 +/- 0.07 vs. 0.30 +/- 0.06, respectively). Of 38 participants undergoing confocal examination, the medication group (n = 19) had fewer nerves (3.8 +/- 2.1 vs. 5.9 +/- 2.0 nerves/frame; P = 0.02) and a lower nerve density (5643 +/- 2861 vs. 9314 +/- 3743 mum/mm; P = 0.007) than the observation patients (n = 10). An additional 9 patients in the observation group, who began medication before confocal scanning, had intermediate nerve densities. Full-thickness keratocyte density was similar, with 22,257 +/- 2419 and 23,430 +/- 3285 cell/mm in the observation and medication groups, respectively.
Chronic administration of glaucoma medications causes a decrease in the number and density of corneal subbasal nerve fiber bundles but does not affect keratocyte density or corneal endothelial characteristics.
[Show abstract][Hide abstract] ABSTRACT: We compared endothelial cell density (ECD) from images recorded by the ConfoScan 3 confocal microscope and a noncontact specular microscope.
Endothelial micrographs of 50 normal corneas of 25 subjects were acquired by a Konan Noncon Robo noncontact specular microscope (Konan Medical, Inc., Hyogo, Japan) and a ConfoScan 3 confocal microscope (Nidek Technologies, Inc, Greensboro, NC). ECD was determined in images from both instruments by using the HAI CAS System Corners Method (HAI Labs, Inc., Lexington, MA). Distances in the images from both machines were calibrated from images of an external scale. Images from the ConfoScan 3 were also assessed using the automated endothelial analysis software provided by the manufacturer, with and without manual correction.
The ECD was 2634 +/- 186 cells/mm(2) (mean +/- SD) and 2664 +/- 173 cells/mm(2) by the Robo and ConfoScan 3 Corners methods, respectively. Differences between these 2 methods were not significant. When the automated analysis software was used, however, significant differences were found (P = 0.001). The uncorrected analysis program provided with the ConfoScan 3 indicated a higher ECD (2742 +/- 284 cells/mm(3)) than the Corners method did with images from the Robo and ConfoScan 3. The ECD from the manually corrected ConfoScan 3 method was 2716 +/- 229 cells/mm(3), not significantly different from the ConfoScan 3 Corners method but significantly different from the Robo Corners method.
The ConfoScan 3 can be used interchangeably with the Robo when the Corners method is used to assess ECD and the magnification of both microscopes is calibrated with an external scale. If the proprietary software provided with the ConfoScan 3 is used, it should be manually corrected.