PubMed1975
Theoretically the contact lens with a refractive power of -64 dioptres is superior to the concave pre-set lens (Hruby lens) or the convex lens (Bayadi). In practice the results are as follows: With the convex lens the examination of the vitreous is unsatisfactory. The reversed image with the convex lens will become familiar with some experience as one will also get used to the mirror images of the three-mirror contact lens. However, the abnormal curvature of the image is really a nuisance. On the other hand the large field of view is an advantage. The convex lens is only practically useful when it can be firmly attached to the slit-lamp microscope, as otherwise the new adjustment necessary for searching the fundus is too difficult. Attachment to the microscope is also of advantage with the Hruby lens. The concave contact lens of 64 dioptres is best suited for detailed examination of vitreous and fundus and for measurements. When no value is placed on a minute examination and a quick simple orientation suffices, the concave pre-set lens (Hruby lens) has the advantage that the lens does not have to be placed on the eye. If it is centred to the middle axis of the microscope, it facilitates especially quick observation. There will be cases where the pre-set lens will be the only answer, especially shortly after an operation or with very sensitive patients. Furthermore, the Hruby lens is preferable to the Bayadi lens because the vitreous can be better examined. The Hruby lens is also advantageous for examination of the region in the middle, lateral periphery of the fundus, 30 degrees - 60 degrees, and is superior in this area to the simple concave contact lens. The Bayadi lens seems to us only indicated for fundus examination of extremely high myopes. There it definitely offers advantages over and above the concave lens. For the most peripheral fundus, expecially below and above, the three-mirror lens with its modification is so far the best method. Especially for examination of the vitreous good brightness of the slit image is required for stereoscopic examination with as large an angle as possible between microscope and illumination. The lateral parts of the most peripheral fundus cannot be examined with the vertical slit in connection with the three-mirror lens. However, this is possible with the horizontal and tilted position of the slit and intermediate positions with an oblique slit. The slit must form an angle with the microscope in order to examine vitreous and fundus in optical section. With the indentation contact lenses ciliary processes and pars plana are now accessible to slit-lamp microscopy.