Answers to the first quick review of what is in the book:

 
1. If the focus is behind the retina the eye has too little plus power, so we give it more plus power in the glasses lens to bring the image into focus on the retina.

 

 
 
 

 When the focus is behind the retina we say the eye is hyperopic. A characteristic of plus lenses is that they are used to correct for hyperopia.
 

2. If the focus is in front of the retina the eye has too much plus power, so we give it minus power in the glasses lens to bring the image into focus on the retina.

 

 
 
 

 When the focus is in front of the retina we say the eye is myopic. A characteristic of minus lenses is that they are used to correct for myopia.
 

3. If the refracting surfaces (cornea and lens) have the power that is considered normal, but the eye globe is too long or to short, we say that the condition is axial.

 

 
 
 

 If the eye globe is 24 mm, but the refracting surfaces (cornea or lens) have too much or to little power, we say that the condition is refractive.