VISION. 241 



for the clinician to deal with, we will omit its deter- 

 mination here. 



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

 following formula for the right eye, -|-2D, 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 of those 

 hyperopes in the class whose punctum remotum 

 may be determined from the lenses which they use? 

 (</) 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 twent)-one to twenty- 

 three, and so on. Determine the average for p and 

 for r from each age column. 

 (0) Does age within the limits of your table affect 



the punctum proximum ? If so, how ? 

 (^) Does age affect the punctum remotum as shown 



by your table ? 



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

 showing the effect of age upon the range of accom- 

 modation. Use the age units for divisions of the 

 axis of abscissas, and dioptre units of p and r for 

 the divisions of the axis of ordinates. 



c. The amplitude of convergence. The fact of the con- 

 vergence of the visual axes of the two eyes in binocular 

 vision has been demonstrated in a previous lesson. We 

 come now to the measurement of this function. 



To measure convergence. To get a clear conception of 

 the situation, let us call the line which joins the centers 

 of rotation of the eyes the base line. A plane perpen- 



