. Refraction and motility of the eye, with chapters on color blindness and the field of vision . Fig. 44. the lens near the margin indicate previous adhesions. Ifthere are spots of this kind or opacities in the cornea, lensor vitreous, they will interfere with the return of light tothe eye of the observer and will appear as black spots orma^es against the red background. Then, while watchingthese closely, the patient is directed to move his gaze up ordown, and the surgeon notes carefully their position rela-tive to the margin of the pupil and can tell quite accuratelyon which of the refractive
. Refraction and motility of the eye, with chapters on color blindness and the field of vision . Fig. 44. the lens near the margin indicate previous adhesions. Ifthere are spots of this kind or opacities in the cornea, lensor vitreous, they will interfere with the return of light tothe eye of the observer and will appear as black spots orma^es against the red background. Then, while watchingthese closely, the patient is directed to move his gaze up ordown, and the surgeon notes carefully their position rela-tive to the margin of the pupil and can tell quite accuratelyon which of the refractive media they are situated. Suppose, for instance, an opacity that when the patient 70 EFFRACTION AND MOTILITY OF THE EYE. looks straight ahead appears like a black point in thecentre of the pupil. When the eye turns upward, it moveswheel-fashion round a centre of rotation, and objects infront of the pupillary plane will seem to move upwardwhile those behind will have a corresponding motion down-ward. If the opacity is in the cornea, it will appear to. Fig. 45. move in the direction in which the eye is turning towardthe margin of the pupil and will finally pass out of theilluminated pupil in front of the iris. If it is in theanterior chamber, it will move in the same direction, butbeing nearer the pupil, will not move so fast nor so far. If on the anterior surface of the lens, which is prac-tically in the same plane as the iris, the opacities willmaintain the same relative position in the pupil, whicheverway the eye may move. If they are in the substance of thelens or on its posterior surface, which are in planes behindthe iris, they are, as it were^ behind the hub of the wheel, OPHTHALMOSCOPY. 71 and, when viewed from the front, seem to move in theopposite direction to the motion of the eye. If theopacities are in the vitreous, they move down when theeye moves up, and vice versa, and their motion is apparentlymore rapid, as they are further from the iris and nearer tothe posteri
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