VISION 201 



infinity; or, better, convergent; but if they are convergent they would 

 meet behind the cornea. The punctum remotum for hyperopes is then 

 negative in direction and is equal to the distance, behind the cornea, at 



which the convergent lines would' meet if prolonged. It follows that - 



is in the case of hyperopes negative. Our formula would then take 

 the form: 



P ( r ), or 

 a = p -f r. 



Now, in determining r one may use a convex lens of such strength 

 as to give the rays the requisite convergence. The value of the lens 

 in dioptres is, of course, the value of r. In the hyperope a is always 

 greater than p. As the determination of the punctum remotum of 

 the hyperopic eye is a matter for the clinician to deal with, we will 

 omit its determination here. 



(6) If a member of the class wears glasses having the following 

 formula for the right eye, +2 D., and if his punctum proximum is 

 12.5 cm. distant from the cornea, what is his range of accommodation? 



(c) What is the range of accommodation for those hyperopes in 

 the class whose punctum remotum may be determined from the 

 lenses which they use? 



(d) May variations in range be accounted for ? 



(e) Is the average range greater or less than that for myopes? 

 For emmetropes? 



(5) Tabulate the values of p and of r for the class; first, with 

 respect to age, arranging in the first column all of the cases which 

 range between eighteen and twenty years; in the second column 

 twenty-one to twenty-three, and so on. Determine the average for 

 p and for r from each age column. 



(a) Does age within the limits of your table affect the punctum 

 proximum? If so, how? 



(b) Does age affect the punctum remotum as shown by your table ? 



(c) If the volume of data justifies it, make a chart showing the 

 effect of age upon the range of accommodation. Use the values of 

 p and r for the divisions of the axis of ordinates. 



XI. NORMAL OPHTHALMOSCOPY (DIRECT METHOD). 



Gould defines ophthalmoscopy as "the examination of the interior 

 of the eye by means of the ophthalmoscope." Normal ophthal- 

 moscopy is the examination, by means of the same instrument, of 

 the normal eye or a model of the normal eye. 



1. Appliances. An ophthalmoscope, with concave mirror; dark- 

 room lamp, and Thorington's skiascopic eye or an equivalent. 



