SECTION VII 



ORGANS OF SPECIAL SENSE 



THE EYE 



BY R. MARCUS GUNN, M.A., F.R.C.S., 



M-.XIOR SURGEON TO THE ROYAL LONDON OPHTHALMIC HOSPITAL, MOORFIK1.DH ; OPHTHALMIC SURGEON TO Till: 



NATIONAL HOSPITAL 



THE EYEBALL AND ITS SURROUNDINGS 



GENERAL SURFACE VIEW 



This examination is to be made prior to any disturbance of the parts, and is, indeed, best 

 conducted on the living body. A pocket magnifying lens should be at hand for use when requin !. 



THE two eyes are situated nearly in the line where the upjxr and middle thirds 

 of the face meet; they lie right and left of the root of the nose, the most 

 prominent part of the front of each globe being about 3 cm. (1J in.) from 

 the middle line of the face. Each eye is overshadowed by the corresponding eye- 

 brow, and is capable of being concealed by its eyelids, upper and lower. 



The orbital margin may Ije traced all round with the finger. At the junction of 

 the inner and middle thirds of the upper margin the supraorbital notch can usually 

 be felt, and the supraorbital nerve passing through it can sometimes be made to roil 

 from side to side under the finger. The inner margin is the most difficult to tnuv 

 in tliis way, partly because it is more rounded off than the others, partly because 

 it is bridged over by a firm fibrous band (tendo oculi, or inner palpebral liga- 

 ment), passing inwards from the eyelids; below this band, however, a sharp bony 

 crest is felt, which iies in front of the lachrymal sac. Note how the eye is pro- 

 tected by the rim of the orbit, above and below; if we lay a hard flat body over 

 the orbital opening, it will rest upon the upper and lower bony prominences, and 

 will not touch the surface of the globe. Inwards, the eye is protected from injury 

 mainly by the bridge of the nose; outwards it is most readily vulnerable, as here 

 the orbital rim is comparatively low. With one finger placed over the closed upper 

 lid, now press the eyeball gently backwards into the orbit, and observe the elastic 

 resist :mee met with, due to the fact that the globe rests posteriorly on a pad of fat. 



The space between the free edges of (lie upper and lower lids is known as the 

 palpebral aperture : it is a mere slit when the lids are closed; but when they arc 

 open its sha|>e Is, roughly, that of an almond lying with its long axis horizontal, 

 and about thirty millimetres in length. 



When the eyes are directed to an object straight in front of them, this aperture 

 is about twelve millimetres \\ide, but its width varies with upward and downward 

 movements of the eyeball, being greatest on looking strongly upwards, diminishing 

 gradually as t he eye looks progressively lower. The antrles formed by the meeting of 

 the lids at each end of the pal[>ebral aperture are named resjx-ct ively the outer and 

 inner canthus, of which the outer, or temporal, is sharp, while the inner, or nasal, 

 is rounded off. On a closer inspection, it will be found that, for the last five milli- 

 metres or so before reachini: the inner canthus. the edsres of the lids run an almost 



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