Optics: Sub And Obj. 2 Flashcards
How is the refractive state of the eye assessed with Photo-Refraction?
Photographing the pattern of light returned from the pupil of the eye
With Photo-Refraction, can both eyes be refracted simultaneously?
Yes
Who would be candidates for Photo-Refraction?
Infants, children, limited attention span and uncooperative individuals
What is the Photo-refraction Refractive error equation?
RRE = d/(2. p. a)
RRE = magnitude of the refractive error relative to the position of the camera; a = distance from camera to subject pupil; p = pupil diameter; and d = diameter of double-pass point spread image.
With photo-refraction, hyperopic eyes will appear in what way?
Red rays will appear in the periphery and blue in the central of the point spread
With photo-refraction, myopic eyes will appear in what way?
Blue rays will appear in the periphery and Red in the central of the point spread
With photo-refraction, where does the far point of hyperopic eyes lie?
Beyond the camera lens
With photo-refraction, where does the far point of myopic eyes lie?
Between the camera lens and the subjects eye
By Photo-refraction method, calculate the magnitude of the Refractive Error (in diopters) of the patient placed at 4 metres from the camera with a pupil size of 6 mm and the measured double pass point spread is 3 cm in diameter.
RRE = 0.625
Or 1.60
By Photo-refraction method, calculate the magnitude of the Refractive Error (in diopters) of the patient placed at 6 metres from the camera with a pupil size of 7 mm and the measured double pass point spread is 3.5 cm in diameter.
RRE = 0.42
Or 2.50
What is the best available method of refraction (gold standard)?
Subjective methods
An aberrometer gives a comprehensive description of ______________.
Eyes optical aberrations
How are aberrations measured with an aberrometer?
By measuring the displacement of each spot from its corresponding lens let axis
Hartmann-Shack aberrometer has an objective lens which is an array of _________.
Tiny lenses
What does the array of lenses in the Hartmann-Shack aberrometer produce?
Multiple images of the same retinal spot of light
What 5 ways contribute to objective and subjective refractions differing?
Chromatic aberrations, Stiles-Crawford Effect, Instrument Myopia, Maximum plus technique, Measurement plane of the instrument
The Phoropter takes measurements in the ________ plane.
Spectacle
The aberrometer takes measurements in the __________ plane.
Corneal
Does refractive error for subjective method change significantly when the pupil dilates?
Not significantly
For a 3mm pupil, was objective refraction hyperopic or myopic to the subjective mean refraction?
Hyperopic relative to subjective mean refraction
For a 6mm pupil, was objective refraction hyperopic or myopic to the subjective mean refraction?
Myopic relative to subjective mean refraction
When Higher order aberrations are small, how is the difference between subjective and objective measurements of refraction?
All metrics give relatively the same refraction
When Higher order aberrations are large, how is the difference between subjective and objective measurements of refraction?
Different metrics give different refractions when HOA are large
How accurate is objective prediction of subjective refraction?
About 2/3rd of the given objective metrics were able to accurately predict subjective refraction within 1/8th of the diopter
