Lec 8: Mag and Blur Flashcards
where is the image axially?
refractive error (K)
where is the image laterally?
retinal magnification
- image size and distortion
- paraxial
A definition of visual angle is necessary in order to quantify what?
retinal magnification and distortion. Visual angle is defined as the angle of the
retinal image subtended at the nodal point of the eye (ω= s/f).
A 1 degree object subtends ____ mm at the retina.
0.3 mm
variation in magnification as a function of field angle. (Note: warps or distorts the image rather than blurs it.)
distortion
Distortion affects what?
both (1) images that form on the retina as well as (2) images that are collected of the retina (what clinicians care about).
In the actual eye, magnification of the retina _____ with field angle.
increases
in the ideal eye, magnification is _________.
constant (no distortion)
How much does retinal magnification (mm/deg) vary across a standard fundus photograph?
Should we account for this change when analyzing a fundus image?
3% difference; we dont really take into account?
How much does retinal magnification (mm/deg) vary across a wide-field fundus photograph?
Should we account for this change when analyzing the image?
23% larger; wide angles make more difference than small angles clinically
- Impact of size and shape of pupil on blur and vision
- paraxial & non-paraxial, (nsinθ = n’sinθ’)
blur and pupil
Retinal blur depends on what?
Retinal blur depends on what?
Visual angle of blur circle B (in radians) is proportional to what?
to focus error E (in diopters) times pupil diameter d (in meters)
B=d|E|
toad pupil shape
heart
catfish pupil shape
horseshoe
