202 SPECIAL PH YSIOL OGY 



2. Preparation. Arrange the model and the lamp so that they 

 will be in the horizontal plane with the observer's eye. Place the 

 skiascopic eye directly in front of the observer's eye, and the lamp 

 a little to one side of the model. 



3. Operation. Let the observer hold the ophthalmoscope with 

 the right hand, mirror forward, close to the eye, directing the vision 

 through the hole in the instrument. Throw the light, reflected by the 

 mirror, into the skiascopic eye. Find the red reflection of the fundus, 

 then gradually lessen the distance between the observer's eye and 

 the model to about 2 cm. or 3 cm. The skiascopic eye will then be 

 illuminated and the fundus with its structures will be clearly defined. 



4. Observations, (a) Adjust the Model to Represent the Emme- 

 tropic Eye. (1) Determine with the ophthalmoscope the color of the 

 fundus. Enumerate the structures seen. 



(2) Describe the papilla, or entrance of the optic nerve. Is the 

 papilla in the visual axis or to one side of it? Describe its position 

 with respect to the visual axis of the eye and determine the most 

 advantageous position of observer, model and instrument, to get a 

 direct view of the papilla in the right eye; in the left eye. 



(3) Describe the location of the arteria and vena centralis retinae 

 with reference to the papilla. 



(4) The ring formed by the border of the papilla is sometimes 

 called the scleral ring or the choroidal ring. Can this ring be dis- 

 tinctly seen? 



(5) The macula lutea and the fovea centralis are the most sensitive 

 portions of the retina and are in a direct line with the visual axis 

 of the eye. 



What is the most advantageous position of model, observer, and 

 instrument in order to get a direct illumination of this part of the 

 fundus? Describe the appearance of the structures in question. 



(6) Describe the retinal bloodvessels minutely, drawing a map of 

 their distribution. 



(6) The Observations of the Retina in the Hyperopic Eye. Adjust 

 the model for three dioptrics of hyperopia. 



(7) Are the retinal bloodvessels distinct when the above-described 

 method of observation is used? 



(8) Place in a rack, before the model eye, the following lenses, 

 with each one testing for a distinct retinal image: 



+ 1 D., +2 D., 4-3 D., and +4 D. 



With which one of the lenses is the clearest image obtained? Are 

 all of the figures of equal size? Explain, giving a figure. 



(9) In hyperopia do the rays focus in front of, on, or behind the 

 retina ? What direction do the rays take after leaving the hyperopic 

 eye from the illuminated retina? Are they parallel, divergent, or 

 convergent ? 



