This video covers the basic optics you need to know to understand basic glasses prescriptions.
length: 24:00 minutes
When I began my ophthalmology residency, I had no idea how to read or write a glasses prescription. In this video, I try to explain the basic topics I wish I had known. This includes lens theory, basic spherical problems (near and far-sightedness), astigmatism, cylinder conversion, and presbyopia (bifocals). While this lecture is “basic” and assumes you have no prior glasses experience … this is still important stuff. I hope you find this useful!
Screen Captures from this Video:
The goal of this video is to completely understand what a glasses prescription
entails.
A lens can be thought of as two prisms … that either converge or diverge light.
A lens rack. The red lenses are "minus" while the black lenses are
"plus"
Lenses are marked with diopter power.
Definition of a diopter is demonstrated, along with lens stacking to create
more powerful convergence.
The eye has an overall power of approximately 60 diopters.
Children tend to be slightly hyperopic as they have small eyes.
Astigmatism is when the corneal surface is more "round like a football"
and less like a basketball.
Children have "with the rule" astigmatism, while elderly tend to have
"against the rule"
The three measurements we check when using the phoropter to "manifest"
a patient
Converting a prescription to minus cylinder
Accomodation of the lens inside the eye
Presbyopia makes it hard to see near objects.
Bifocal power. We rarely prescribe greater than 3 diopters as few people read
much closer than 1/3rd of a meter (33 centimeters).
