PubMed · 7239809
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N J Bailey. 1981. Lens verification and modification.. https://pubmed.ncbi.nlm.nih.gov/7239809/
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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.
PURPOSE: The clinical importance of the edge lift of rigid contact lenses is often neglected, possibly due to previous difficulties in its measurement. A new method of measuring axial edge lift (AEL) and radial edge lift (REL) using standard contact lens verification equipment, such as an optical spherometer, a thickness gauge, and contact lens V gauge, is described. METHODS: The technique was validated for trueness (accuracy) and precision (repeatability) by measuring the edge lift of a number of monocurve lenses, manufactured both with and without a normal edge finish. RESULTS: Edge lift was measured to an accuracy of 0.01 mm. CONCLUSIONS: As long as a mean of eight independent measurements of back optic zone radius (BOZR), sagitta, and one measurement of center thickness are taken, the pillar and collar technique is capable of producing accurate and repeatable measurements of the edge lift of a rigid contact lens.
BACKGROUND: The method of using an optical spherometer and a lens thickness gauge, in combination with a pillar and collar, has previously been shown to be repeatable and accurate (to 0.01 mm) in measuring the edge lift of rigid monocurve lenses. PURPOSE: This paper goes on to validate the technique for measurements taken on edge-finished multicurve rigid lenses. METHODS: The axial edge lift (AEL) of a series of multicurve rigid lenses having known values of AEL was measured using an optical spherometer, a thickness gauge, and contact lens V gauge in a similar way as was described in the companion paper. RESULTS: The results show that as long as a correction factor of 0.01 mm is applied, as found in the previous paper, the technique will allow satisfactory verification of the edge lift. CONCLUSIONS: The technique is accurate and reproducible, even in multicurve lens designs, provided that a calibrating correction factor of 0.01 mm is applied to account for methodological error. It will also indirectly allow the accuracy of manufacture of the peripheral curves and diameters of any rigid contact lens to be verified.