The Naked Scientists

The Naked Scientists Forum

Author Topic: How does the machine know what glasses are right for me?  (Read 3464 times)

Offline chris

  • Neilep Level Member
  • ******
  • Posts: 5339
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Modern eye tests rely less on an optician asking a patient what looks right and more on a machine that measures the required refractive correction and then tells the optician what prescription to try.

How does this machine measure what lens strength is required?

Chris


 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
How does the machine know what glasses are right for me?
« Reply #1 on: 06/03/2009 13:16:01 »
Modern eye tests rely less on an optician asking a patient what looks right and more on a machine that measures the required refractive correction and then tells the optician what prescription to try.

How does this machine measure what lens strength is required?

Chris
Don't know, but I presume it could measure all the curvatures of the crystalline by reflecting light off it (I'm just speculating).
 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8134
  • Thanked: 53 times
    • View Profile
How does the machine know what glasses are right for me?
« Reply #2 on: 06/03/2009 20:03:26 »
Quote
Retinoscopy is a technique to obtain an objective measurement of the refractive condition of a patient's eyes. The examiner uses a retinoscope to shine light into the patient's eye and observes the reflection (reflex) off the patient's retina. While moving the streak or spot of light across the pupil the examiner observes the relative movement of the reflex then uses a phoropter or manually places lenses over the eye to "neutralize" the reflex.
 
Retinoscopy is especially useful in prescribing corrective lenses for patients who are unable to undergo a subjective refraction that requires a judgement and response from the patient (such as mentally handicapped or non-verbal people).

Retinoscope works on a principle called Foucault's principle. Basically it indicates that the examiner should simulate the infinity to obtain the correct refractive power. Hence a power corresponding to the working distance is subtracted from the gross retinoscope value.
http://en.wikipedia.org/wiki/Retinoscopy
 

lyner

  • Guest
How does the machine know what glasses are right for me?
« Reply #3 on: 06/03/2009 23:23:22 »
It boils down to an autofocus system which produces the correct lens prescription to produce a well focused image of the retina at infinity - or wherever you want it. Piece of cake nowadays, with camera technology.
I was very impressed in the 1970s when a guy in Surrey, effectively did the same thing 'manually'. He only required a slight tiffle, during the reading test, to produce the correct prescription for me. He just asked me to focus on a distant object whilst doing the measurement.
 

The Naked Scientists Forum

How does the machine know what glasses are right for me?
« Reply #3 on: 06/03/2009 23:23:22 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums