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. The goal of the study is to measure the group refractive index of the human cornea in vitro to improve the accuracy of conical thickness measurements. Methods. Corneal buttons were trephined from 23 human cadaver eyes and the group refractive index ofthe cornea was measured at =840 urn using a low-coherence Michelson interferometer and the technique proposed by Sorin and Gray (Phot. Tech. Letz 4: [105][106][107] 1992). The effect of dehydration on the measurement was Studied by measuring the conical optical thickness as a function of time. Results. Preliminaiy measurements of the group refractive index at 840 nm gave flg 1.450 +/ 0.024 for the human cornea, which is much higher than a calculated group refractive index of flg 1.387. BCcLUS of dehydraüon, the optical thickness of the cornea decreased at a rate of 5.5 pim/min which led to an artificially high value for the group refractive index. Conclusion. The calculated group refractive mdcx of rig 1.387 ppC&S to be an accurate value for the purpose of cornea! thickness measurements using low-coherence interferometiy, and cornea! group refractive index measurements can be performed in vitro ifthe measurements are performed rapidly to avoid the effect of dehydration.
Photothermotherapy is not without risk unless the temperature field can be well adapted to the tumorous structure, as temperature elevations outside a small therapeutic range that affect vital structures are considered to be a risk factor.
The specific advantages of a number of integrated optical systems, consisting of optical probes of various shapes and materials, coupled to a number of optical fibers are described. The radiation fields of the various systems vary significantly in their performance and the clinical effects may be expected to vary correspondingly. This is a step forward in the theoretical evaluation of optimal laser microsurgical tools for specific applications.
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