Practical - Physiology of Vision Flashcards
Visual acuity and blind spot is calculated using what?
similar triangles
What is emmetropia?
Normal vision
Neither long or short sighted
What is hypertropia?
Long sighted
What is myotropia?
Short sighted
How is hypertropia corrected?
Convex lens
How is myotropia corrected?
Concave lens
How is long and short sight tested?
Duo chrome test
Long sighted = green chart is more clear
Short sighted = red chart is more clear
Due to the two colours having different wavelengths
What does the visual acuity test consist of?
determine maximum distance at which subjects can distinguish between parallel lines
Calculate via similar triangles equation
What is Snellen’s test and what does it test for?
Measures slight degrees of impairment in visual acuity
Row of letters descending for large to small
Normal vision is reading largest letters from 60m and smallest from 6m
Test each eye separately
Result given as a ratio
What is regular astigmatism?
The shape of the eyeball is not perfectly spherical but almost squashed to produce a more spoon shaped
Still a even surface
What is irregular astigmatism?
The shape of the eyeball is indented either from the edge or on the surface so that it is very uneven
What shaped lens is used to correct regular astigmatism and how does it work?
Cylindrical
Works as it the same shape of the pupil and it placed perpendicular to make the lens look rounder
What shaped lens is used to correct irregular astigmatism and how does it work?
Spherical
Makes the pupil a more rounded even shape
What is the difference between relative and absolute visual acuity?
relative visual acuity = visual acuity of an uncorrected eye
absolute visual acuity = measure of the acuity with the best correcting glasses
What is the blind spot test used for?
demonstrates the presence of the blind spot
in an area of the retina known as the optic disk
