PubMed · 8261601
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O D Solomon. 1993. Micropachometry.. https://pubmed.ncbi.nlm.nih.gov/8261601/
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This is a review of optical methods related to biomicroscopy and laser treatment of the posterior segment of the eye. Contact lenses can be used to observe optical structures and couple laser radiation into the eye for a vast range of conditions and techniques. A small laser spot size is indispensable for photodisruptive work, though this requires a large beam diameter at the pupil and therefore optical systems and techniques such as scleral indentation which maximize the pupillary beam diameter are preferred. For coagulation work the choice of beam focusing optics is crucial for optimum safety. Vitreous replacement can be used to change the refractive power of the eye and permit new combinations of treatment and optical systems. This review covers many aspects of laser irradiation of the eye. It should be clear that, with the multitude of different procedures and optical systems involved, the laser surgeon is faced with a daunting task in assessing and meeting safety limits.
PURPOSE: To assess the efficacy of computerized corneal topography in (1) fitting cosmetic rigid gas permeable contact lenses on normal corneas and (2) patients who have keratoconus. METHODS: In study 1, 26 patients were fitted with cosmetic contact lenses. In 13 patients, the first rigid gas permeable lens was chosen on the basis of corneal topography using the EyeSys videokeratoscope and contact lens software version 2.11w. Thirteen control patients were fitted with rigid gas permeable contact lenses by means of diagnostic contact lenses. The number of parameter changes required in each group to reach the best fit were compared. In study 2, the records of 28 patients (41 eyes) with keratoconus who had been successfully fit with rigid gas permeable lenses were reviewed. Topographic analysis using the EyeSys videokeratoscope was conducted. The following 8 data points were analyzed: maximum dioptric curvature with respect to the central visual axis, the power at the visual axis (VK), the average keratometry readings within the 3-mm zone, the average flat K at 3-mm central and 5-mm paracentral regions, and the K reading at 1.5, 2.0, and 2.5 mm superior to the visual axis. RESULTS: Study 1: In 10 eyes (38%) fitted with cosmetic contact lenses utilizing corneal topography and the EyeSys contact lens program, the first lens chosen by the computer program was correct with no additional changes in lens parameters required. In the other 16 eyes, 21 parameter changes were required. In the control group, 14 eyes (53%) required no additional change in parameters from the original contact lens that was fitted using diagnostic lenses. In the other 12 eyes, 12 parameter changes were required. Study 2: In the keratoconus group, of the 9 measurements analyzed, the final base curve of patients' rigid gas permeable lenses was correlated most closely with the average flat corneal curvature at the 3-mm central zone. CONCLUSION: Study 1: In fitting cosmetic rigid gas permeable contact lenses, the videokeratoscope with the EyeSys software 2.11w contact lens program proved to be inferior to diagnostic lenses in selecting the final correct contact lens parameters. However, it may be useful in selecting an initial diagnostic lens with which to begin rigid gas permeable fitting. Study 2: In patients with irregular corneas such as keratoconus, corneal topography is helpful in determining the initial base curve of the contact lens. In patients with keratoconus, it appears to be the average flat corneal curvature at the 3.0-mm zone.
Measurements of optic disc diameter with the Zeiss 4-mirror contact lens and 78 dioptre (D) lens, made by projecting a slit-beam of known height onto the image of the disc, were compared with planimetric measurements in 30 eyes. The 78 D lens measurements were significantly larger than both the Zeiss lens and planimetric measurements (p < 0.0001 and p = 0.0047 respectively). The measurements using the Zeiss lens and planimetry did not differ significantly. Compared with planimetry, for the 24 eyes within 3 D of emmetropia, the correlation was greater for the Zeiss (r = 0.8591) than for the 78 D lens (r = 0.7148). The Zeiss lens also showed better agreement and less scatter of results compared with the 78 D lens (standard error of the mean +/- 0.0373 mm for the Zeiss and +/- 0.0418 mm for the 78 D lens). The Zeiss contact lens measurements of optic disc diameter show stronger correlation and better agreement with planimetry than measurements using a 78 D lens.