Fig. 3 USES OF CONTACT GLA SSES.—There are two classes of casein which contact glasses maybe usefully employed. First—cases in which a contact glass is used to improve the vision and second—cases in which a contact glass is used for protection of the eye-ball. i. Cases in which a contact lens is worn in order to improve the vision. (a) Conical cornea (keratoconus).—The degree of irregular astigmatism caused by this condition, in which there is a bulging of the centre of the cornea due to degenerative thinning is often so great that it cannot be corrected with ordinary glasses. This means in many cases that the patient is unable to read the top letter of the ordinary Snellen Test Type at 3 yards even with the best glasses whereas a contact lens will often allow all the letters on the chart to be read at the full distance of 20 feet. (b) Myopia (short-sightedness) .—This condition, particularly in its severer forms is an indication for the use of contact glasses especially for those whose occupation makes the wearing of glasses undesirable e.g. actresses public speakers and those who are exposed to dust high winds and steamy and foggy atmospheres. Fig. 2 shows a patient with myopia wearing ordinary correcting lenses and Fig. 3 shows the same patient wearing contact glasses. Note the fact that the contact glasses are almost invisible except when the wearer is looking far to one side. (c) Unilateral aphakia i.e. the removal„ or traumatic destruction of the lens of one eye.— In this condition binocular vision when wearing an ordinary glass fitted into a spectacle frame is quite impossible, but with the aid of a contact glass worn on the affected eye restoration of binocular vision is brought about. An example of the value of a contact glass is afforded by the following case:— S/Ldr. S.C.R. aged 29 a fighter pilot. Received injury to face and right eye by means of cannon shell, which burst onto his machine causing his hood to be damaged and fragments of Perspex to be showered into his face. He sustained a perforating wound of the right eye from a sharp piece of Perspex which penetrated the cornea and lodged in the crystalline lens of the eye. After two operations in which first the cataractous lens was removed and subsequently the small foreign body by means of a special pair of forceps his vision was correctable to 6/6 with a +12 D .spherical lens. His vision in the other eye was normal. Two months after the injury he was fitted with a contact lens for his damaged eye which gave him normal binocular vision. The vision of the injured eye could have been corrected by means of a thick convex lens worn in an ordinary spectacle frame, but he would have been unable to use both eyes together to obtain binocular vision as owing to the indifference size of the images as seen by each eye, he would have had double vision. Without the contact glass this officer would have been unfit for further flying duties whereas he is now back at work doing full flying duties. 2. Cases in which Contact Glasses are of value for protective purposes. Contact Glasses have a valuable but as yet not fully explored protective scope. This group of cases maybe sub-divided into two classes. (1) Those in which Contact Glasses are used to avoid certain hazards. In some instances Contact Glasses maybe worn as a purely protective medium by those who, in normal circumstances do not require to wear glasses. In other cases Contact Glasses are worn as a substitute for ordinary glasses. (2) Those in which Contact Glasses are worn to protect the cornea of the eye for pathological reasons. Into this class fall:— 1. Those whose occupation involves accidents in which ordinary spectacles might be broken
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