[Microsurgery in ophthalmology].

The use of operating spectacles goes back just over one hundred years; the first were simple presbyopic corrections, later increased to over-correction and later coupled with the use of base-in prisms. Magnification was increased by displacement on the nose to increase the back vertex distance. About 1880, the limited magnification available with a single lens was overcome by the use of compound lens systems and this led on naturally to the introduction of the microscope. Basically the single vision lens has a maximum of x 1 5 with a 6 dioptre lens. With a compound system it is possible to have effective magnification up to x 5, but it is impractical beyond this magnification because of the small visual field at 20 cm. (which would in fact be two-thirds of a sq. cm.) and because of movement; head quiver leads to disturbed visual sensations on the part of the surgeon. The movement of the field is in the opposite sense to the movement of the head and exactly proportional to the magnification. With a fixed microscope one can increase the size of the telescope allowing stability and increased field; the movement of the surgeon has no greater effect on the movement of the field than without magnification. The binocular microscope was used first in the laboratory and then introduced into ear, nose and throat surgery. Nylen (1954) described the development of the operating microscope from 1921 until 1953. The first microscopes were rather crude devices which took fixation from the bony structures of the skull and were of monocular type. It soon became established that a magnification of about x 10was most popular among surgeons and this proved to be the most suitable magnification for binocular microscopes. The working distance became established and the ideal for most surgeons has proved to be about 30 cm., for which, in fact, most of the modern operating microscopes are built. Intermediate change of magnification became available without altering the working distance (Littmann, 1954). As the microscopes were developed, the stability of the stand improved with additional facility of movement. Although it was Nyle-n (1921-22) who first advocated the use of the operating microscope, it was Holmgren who subsequently took up its development and popu-