Classification of Anterior and Posterior Elevation and Axial Curvature Maps of Cornea using the Orbscan in Myopic Eyes

PURPOSE: To evaluate anterior and posterior elevation maps and axial curvature maps in myopic eyes. METHODS: One hundred and four eyes of 52 myopic patients were investigated using the Orbscan (Orbtek, Inc., USA). The anterior and posterior maps were defined as PAR CTS. And the axial curvature maps were designated as Bogan's classification. We got the distribution and astigmatism power of every map patterns, and the similarity of both eyes under map patterns. RESULTS: Island (37.5%) was the most common anterior elevation pattern, and regular ridge (36.5%) pattern was the most common in posterior corneal surface. There was more significant astigmatism in regular ridge and irregular ridge patterns than incomplete ridge in anterior corneal surface. And astigmatism was more significant on regular ridge than incomplete ridge in posterior corneal surfaces. There was no significant difference between topography of anterior and posterior corneal surface. In axial curvature maps, symmetric bow tie was 35.6% of 104 eyes, and irregular, oval, asymmetric bow tie, round were observed in 27.9%, 18.3%, 13.5%, 4.8%, respectively. Mean astigmatism was significantly high on symmetric bow tie than round. Similarity of both eyes was 50% in anterior elevation maps, 26.3% in posterior corneal surface, and 59.6% in axial curvature maps. CONCLUSIONS: Anterior and posterior elevation and axial power corneal topography maps using the Orbscan were useful for evaluation of normal cornea and preoperative and postoperative corneal status at refractive surgery. But, there were many irregular types and low similarity of both eyes relatively.

A Study on Central Corneal Pachymetry Maps with Orbscan Corneal Pachymetry System in Myopic Eyes

PURPOSE: To evaluate central corneal thickness and pachymetry maps in myopic eyes. METHODS: 104 eyes of 52 myopic patients were investigated using the Orbscan (Orbtek, Inc., USA). The pachymetry maps were designated as round, oval, decentred round, and decentred oval. Corneal thickness was evaluated at the central, eight-paracentral, and the thinnest sites on each of the corneas. We studied difference of corneal thickness under sex and myopic degree. And got the symmetry of the cornea under location of the thinnest sites. RESULTS: Superior cornea had the greatest average thickness (605.5+/-35.3 mu m). Average central corneal thickness (+/-SD) was 552.2 (+/-34.9) mu m. All corneas had the thinnest sites on 0.86 mm from the visual axis and most of all inferotemporal area (76.0%). There was no significant difference of corneal thickness in sex and myopic degree. Average thickness of the thinnest sites was 544.2 (+/-35.6) mu m and significantly thinner than center. 61.5% of the persons had symmetrically located thinnest corneal sites and most of all (57.7%) had temporal side symmetry. In the pachymetry maps, oval pattern was 47.1% of 104 eyes, andround, decentred oval, decentred round were observed in 43.3%, 5.8%, and 3.8% of eyes, respectively. CONCLUSIONS: Of all myopic eyes evaluated in this study, the thinnest sites were on average 0.86 mm from the visual axis. And oval type was the most common pachymetry map pattern.

Two Types of Retinal Capillary Path in Humans using Fluorescein Leukocyte Angiography

PURPOSE: To explain hypothesis that there are two types of human retinal capillary pathways. One is simple type and the other is complex type. The former plays a role in blood flow regulation and the latter does capillary function itself. METHODS: We measured the length, tortousity, and flow velocity of human retinal capillaries using Fluorescein Leukocyte Angiography (FLA) with a Scanning Laser Ophthalmoscope (SLO) on two healthy adult male volunteers. We studied distribution and pathways of human retinal capillaries on the posterior pole. RESULTS: The lengths of capillaries were distributed with two peak incidence. One was 70 microgram and the other 240 microgram. There was no relationship between capillary length and tortousity. The correlation between capillary length and leukocyte velocity showed that the shorter capillary group has a wide range of velocity but the longer group has a narrow range of velocity. CONCLUSIONS: Two types of retinal capillary pathways exist on human retina. Compared with two types of capillaries on the cat retina described by Ben-nun et al, we found that the shorter capillary type plays a role in blood flow regulation and the longer type in capillary function itself.