PubMed · 9209978
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1997. Consultation section. Refractive surgical problem.. https://pubmed.ncbi.nlm.nih.gov/9209978/
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Grading scales have been developed to assist practitioners in recording the level of severity of ocular complications of contact lens wear. Eight common complications are depicted in five levels of severity--from grade 0 (normal) to grade 4 (severe). The intersubject variance in grading was determined to be 1.0 scale units, which by coincidence concurs exactly with the key design strategy of the grading scales that each grading step of 1.0 corresponds to a clinically significant difference in severity.
BACKGROUND: Some months ago we described morphological changes in the stroma of the cornea of patients with a history of long term contact lens wear. These degenerations consist of little highly reflective structures called "micro-dots". For a more precise quantification of the micro-dots we established a clinically practicable method for measuring and counting. MATERIAL AND METHODS: The micro-dots can be visualized in optical sections with the scanning slit confocal microscope. To get the real thickness of a single optical section we had to develop a in vitro model, which consists of a gel of agar with particles of latex of different size. RESULTS: Some stereological methods made it possible to calculate the thickness of an optical section as seen with the confocal microscope. We found out that the thickness shows a variation depending on the reflectivity and size of the particles as well as on the aperture of the objective used. From the area of the frame and the thickness of the optical section we could calculate the density of the highly reflective particles. DISCUSSION: Up to now we could determine the morphological changes (micro-dots) in the cornea of patients with a history of long term contact lens wear in a semiquantitative manner only. With the presented method we are able to make a quite precise numerical estimation of micro-dots. This is very useful to follow up the progress of these stromal changes over many years.
PURPOSE: The aim of this research was to develop a corneal topographer that determines the shape of the entire anterior surface of an eye without assumptions, and with uniformly high accuracy in the center and periphery. METHODS: Based upon a double projection of two sine wave gratings and analysis of the distortion of the sine wave gratings due to the corneal-scleral shape, point-by-point measurements of surface elevation were obtained with a sample density equal to the pixel density of the CCD-detector. Using this principle, a prototype topographer, called the Maastricht Shape Topographer (MST), was developed. The accuracy and reproducibility of the instrument were evaluated using bispheric models of the anterior surface of the eye. RESULTS: The average accuracy of height measurements was +/- 0.55 micron in the 10-mm central area and +/- 22.50 microns in the periphery (14 to 19 mm). Reconstruction accuracy of the radius of curvature was +/- 0.0155 mm (+/- 0.88 D) in the center and +/- 0.0313 mm in the periphery (sclera). Average height reproducibility standard error was 0.0282 micron in the center and 2.6156 microns in the periphery. CONCLUSIONS: With the MST, unambiguous shape measurements of the entire anterior surface of the eye are possible, with accuracy up to clinically accepted standards. MST is able to measure height over a wide area of 20 mm, with a 6-mm depth of field. The tested prototype of the device can be further improved by the use of custom-made optics in order to increase signal to noise ratio in the periphery of the image. This height topographer could offer a reliable method in cases where shape is of paramount importance, e.g., in (scleral) contact lens fitting and refractive surgery.