B Understanding Corrective Lenses: Examining Reversed Prescriptions

  • B
  • Thread starter Thread starter Flyboy
  • Start date Start date
  • Tags Tags
    Lens
AI Thread Summary
Understanding corrective lenses involves recognizing that diopter powers are additive, meaning wearing glasses with a reversed prescription can provide insight into what someone with nearsightedness experiences without lenses. For example, if someone has a prescription of -3.0 diopters, using +3.0 reading glasses can simulate their uncorrected vision. However, factors like astigmatism and individual differences in focus range can complicate this approximation. A more effective method is to compare the distances at which both individuals can read, such as street signs. Additionally, if the prescription includes a prism, it indicates astigmatism, which may cause visual distortions when the glasses are rotated.
Flyboy
Gold Member
Messages
423
Reaction score
626
My girlfriend has started wearing corrective lenses to address some nearsightedness and I'm not fully understanding what she's going through, or what the difference is for her with and without glasses. I was curious if you basically reversed the prescription of the lenses, would it take my normal vision and give me an idea of what she's seeing without the lenses?
 
Science news on Phys.org
I believe that to first approximation that the diopter powers of lenses are additive. So if your friend has a correction of, say, -3.0 diopters you should be able to get a sense for what her uncorrected eyesight is like by wearing +3.0 "reading" glasses. You can find those at a pharmacy. They don't require a prescription and they are inexpensive.

Or maybe I'm wrong.
 
  • Like
Likes sophiecentaur and berkeman
JT Smith said:
Or maybe I'm wrong.
Nope, you had it right - diopters add. However, there are complicating factors. She may have some astigmatism. Her eyes might have different range of focus from yours, so your eyes might partially compensate for the reading glasses.

A better test is to compare the distances at which you and she can read, for example, street signs.
 
JT Smith said:
You can find those at a pharmacy.
And they are typically just sitting in open display on a shelf or at a small kiosk. They are meant to be tried on, so you don't even have to buy a pair to get an idea. Just look at your GF's Rx and as mentioned above, pick the pair or reading glasses with the complementary Rx in diopters and look around as you stand there. Can you say what her optical Rx is?
 
Not off the top of my head, wanted to make sure I was understanding the physics right.

I do know she has a little prism to hers, which I don't think reading glasses have, but the reading glasses is a good idea for an approximation.
 
If 'prism', that suggests a degree of astigmatism. Try rotating her glasses while looking through them. The result may be disconcerting as eg verticals blur vs horizontals, then vice-versa...
 
Thread 'A quartet of epi-illumination methods'
Well, it took almost 20 years (!!!), but I finally obtained a set of epi-phase microscope objectives (Zeiss). The principles of epi-phase contrast is nearly identical to transillumination phase contrast, but the phase ring is a 1/8 wave retarder rather than a 1/4 wave retarder (because with epi-illumination, the light passes through the ring twice). This method was popular only for a very short period of time before epi-DIC (differential interference contrast) became widely available. So...
I am currently undertaking a research internship where I am modelling the heating of silicon wafers with a 515 nm femtosecond laser. In order to increase the absorption of the laser into the oxide layer on top of the wafer it was suggested we use gold nanoparticles. I was tasked with modelling the optical properties of a 5nm gold nanoparticle, in particular the absorption cross section, using COMSOL Multiphysics. My model seems to be getting correct values for the absorption coefficient and...
Back
Top