Biomedical Engineering Reference
In-Depth Information
A
B
Emmetropia
Ametropia
Figure 13-2.
A.
In refractive ametropia, image blur is not due to the axial length being
too short or long.
B.
Refractive ametropia results in a blurred retinal image, but does
not affect the image size.
the projector lens is made too strong or too weak.
The take home message is
that in uncorrected refractive ametropia, the image is the same size as in
emmetropia.
RETINAL IMAGE SIZE IN
CORRECTED AMETROPIA
Before talking about retinal image size in corrected ametropia, let's recap what
we've learned so far about spectacle magnification and retinal image size in
uncorrected
ametropia:
• A plus spectacle lens causes magnification.
• A minus spectacle lens causes minification.
• A contact lens causes no magnification (or minification).
• In axial myopia, the retinal image is larger than in emmetropia and in axial
hyperopia, it is smaller than in emmetropia.
• In refractive myopia and hyperopia, the retinal image is the same size as in
emmetropia.
