Magnification and Field of view Flashcards
Give the equation for calculating the magnification for an emmetropic eye?
beta/alpha
size of an object through an ophthalmoscope/ size of an object at least distance of distinct vision
Define magnification
how much bigger the object appears through the ophthalmoscope than if observed with the naked eye
what is dioptric length of a standard reduced eye?
+60D
what is the equation for linear extent of useful field of view?
j (m)= g x (K-W)/ Fe
g= pupil size K= ocular refraction W= reciprocal of working distance (-ve) Fe= dioptric length of an eye
State the relationship between working distance and field of view?
if working distance is high, the field of view is low
State the relationship between working distance and field of view?
if pupil size is small, the field of view is small
state the relationship between refractive error and field of view?
if Rx is +ve, FOV is high
if Rx is -ve, FOV is low
Give the equation for magnification of an ammetropic eye?
M= Fe/4 x 1/(1-wK)
M= magnification Fe= dioptric length of an eye w= working distance (-ve) (not the reciprocal ) K= ocular refraction
What is the magnification for the following:
1) Emetrope
2) Myope
3) Hyperope
1) emmetrope= 15
2) myope= greater than 15
3) hyperope= lower than 15
where does the light form the ophthalmoscope focus?
behind the retina
where does the blur circle form?
on the retina
what are the 4 factors that affect FOV and magnification?
- ametropia (accounts for hyperopia, myopia and astigmatism)
- pupil size
- sight hole size
- working distance
State 5 requirements for a good ophthalmoscope?
- minimise corneal reflections
- clear, uniform light patch
- FOV coincident with light patch
- range of target apertures
- absence of sight hole flare
