Lenses

By: Carmen Willings
teachingvisuallyimpaired.com
Updated June 13, 2025​
Reports should indicate what a student's uncorrected (without glasses) and corrected (with glasses) visual acuities are. If a student's vision can be corrected, even mildly, they will typically be prescribed glasses or contacts. ​

​Why were the glasses prescribed?

It is important to know why the glasses have been prescribed. Correcting a refractive error (such as myopia or hyperopia) is only one of the reasons that these may be prescribed. ​Glasses may be prescribed with a prism for a muscle imbalance or they may be recommended to protect the eyes. If the glasses are prescribed for near, they should be removed for distance viewing and vice versa if recommended by the doctor (some students will be able to leave them on as it will not have a significant impact). Glasses that are prescribed for myopia, or nearsightedness, will have a minus lens. Glasses prescribed for hyperopia will have a plus lens.

​Types of Lenses

The type of lenses that are prescribed can tell you a lot about the student's eye condition. The stronger the lens, the more significant the uncorrected vision. Keep in mind that even if a student is prescribed glasses, it doesn't necessarily mean that the student's vision can be fully corrected. This is because glasses cannot correct all types of visual impairments.
Convex (Plus) Lenses
  • Shape: Bulges outward
  • Function: Converges light rays; makes images appear larger
  • Corrects: Hyperopia (farsightedness)
  • Notes: Lenses stronger than +12D may suggest: extreme farsightedness or Absence of the natural lens (aphakia)
Concave (Minus) Lenses
  • Shape: Bulges inward
  • Function: Diverges light rays; makes images appear smaller
  • Corrects: Myopia (nearsightedness)
  • Notes: Very strong minus lenses suggest high myopia
Plano Lenses
  • Shape: No bulge; flat
  • Function: No corrective power
  • Uses: Balance prescriptions (e.g., no vision in one eye), Cosmetic purposes, or Eye protection
Prism Lenses
  • Function: Redirects light to aid eye alignment
  • Used For: Strabismus (eye turn), or visual field neglect (helps cue attention to neglected side)
  • Base: Indicates direction the prism shifts light (e.g., base-in, base-out, base-up, base-down)

​Other Prescription Terms

  • Sphere (SPH): The amount in diopters of correction to sharpen vision to best correction.
  • Cylinder: Amount of lens power needed to correct astigmatism.
  • Axis: Orientation of astigmatism correction (in degrees)
  • Prism: Added to some prescriptions to compensate for eye alignment problems.
  • Base: Location of the thickest edge of the prism and direction it redirects light. 

Sample Eyeglasses Prescription

 
 
Sphere
Cylinder
Axis
Prism
base
Distance
OD
-3.75
 
 
0.5
down
 
OS
-4.25
-0.50
180
0.5
up

All About Vision

Gary Heiting, OD has written a great article for All About Vision entitled "How to Read Your Eyeglass Prescription." This information can be very helpful when interpreting the eye report!
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