204 SPECIAL PHYSIOLOGY 



(c) Observation of the Myopic Eye. Adjust the model to represent 

 3 D. of myopia. 



(5) Does the increase of the distance of the lens from the eye cause 

 the image of the papilla to become altered in size or reversed in posi- 

 tion? Account for all phenomena. 



(6) If the position of the +12 D. lens, which the observer holds, 

 remains the same 8 cm. from cornea will there be any variation 

 in the distance from the cornea of the retinal image for the hyperopic 

 eye and myopic eye? Will the distance of the hyperopic eye be 

 greater or less than for the emmetropic eye? Why? 



(d) Observation of the Human Eye. At this point of the student's 

 work, let him practice the direct and indirect method of ophthalmos- 

 copy upon his comrades; after two or three days of practice he may 

 pass to the following exercise. 



XIII. SKIASCOPY. 



Gould defines skiascopy as " a method of estimating the refraction 

 of the eye by observation, through ophthalmoscopic mirror, of the 

 movements of the retinal images and shadows." Synonyms: Fundus 

 reflex test; umbrascopy; pupiloscopy; koroscopy; kertoscopy; retin- 

 oscopy, etc. 



1. Appliances. A simple retinoscope or an ophthalmoscope 

 with a plane mirror; Thorington's skiascopic eye or an equivalent; 

 dark-room lamp, etc. 



2. Operation. The observed eye and lamp are to have the same 

 relative position as in ophthalmoscopy. Let the observer sit directly 

 in front with the eye in the same horizontal plane with the lamp and 

 observed eye, and somewhat more than 1 m. distant from the observed 

 eye. Throw the light reflected by the mirror into the observed eye; 

 rotate the mirror slowly and a shadow will be seen in the pupil of the 

 observed eye. 



3. Observations, (a) Observation of the Emmetropic Eye. Adjust 

 the model to represent emmetropia. 



(1) Does the shadow move in the same direction as the mirror 

 rotates or in the opposite direction i. e., does the shadow move with 

 the mirror or opposite? 



(2) Is the movement of the shadow quick or slow? 



(b) Observation of the Myopic Eye. (I) Adjust the model to represent 

 less than 1 D. of myopia. 



(3) Note that the shadow movement is with the direction of the 

 mirror rotation, and that it is relatively quick. 



(II) Adjust the model to represent a myopia of more than 1 D. 



(4) Note that the shadow movement is opposite the direction of 

 the mirror rotation, and that it is quick when the myopia is of low 

 degree; slow when of high degree. 



