Refractive Error

Question 1

Refractive error

Answer 1

what is wrong with eye

Question 2

Refractive correction

Answer 2

what is needed to correct that error

Question 3

Myopia

Answer 3

short-sightedness
can see close up but not far away
optical system of eye too powerful for its length
minus lens, concave lens- thicker at edges than at its centre

Question 4

Hypermetropia

Answer 4

long-sightedness
can’t see anywhere without error
optical system of eye not powerful enough for its length
called hyperopia in USA
plus lens, convex lens- thicker at centre than at it edges

Question 5

Astigmatism

Answer 5

eye’s optics have 2 different curves at right angles to each other (rugby ball shape)
can be corna, lens or both
can’t focus on anything properly without specs
eye has 2 different powers so to correct: lens has 2
different powers (cylinder lens)

Question 6

Presbyopia

Answer 6

affect everyone >45 yrs old (normal change)
lens stiffens as we age and grows a little too big
can no longer adjust for near vision
typical symptom- arms not long enough to read something
occurs in addition to other refractive errors- need different powered lenses for different working distances

Question 7

Strabismus (heterotropia, squint)

Answer 7

eye not pointing at same thing
turned in- esotropia
turned out- exotropia
turned up- hypertropia
turned down- hypotropia

concomittant- same in all directions of gaze
incomittant- varies with direction of gaze
accomodative- depends how much focusing effort is being exerted

Question 8

Heterophoria (latent squint)

Answer 8

eyes look normal (can't spot it)
eyes not pointing at same thing when one eye is covered
wants to turn in- esophoria
wants to turn out- exophoria
wants to turn up- hyperphoria
wants to turn down- hypophoria
R hypophoria = L hyperphoria (usually)

Question 9

Diplopia (double vision)

Answer 9

usually due to misalignment of eyes
can occur in strabismus
can occur in heterophoria if eyes are strained and can no longer compensate
can be dangerous- risk of falls in elderly
can be uncomfortable- eye strain
can also be monocular eg in cataract

Question 10

Convergence (not a refractive error or binocular vision problem- more a binocular vision feature)

Answer 10

either inability to converge enough or inability to maintain convergence
convergence insufficiency

Question 11

Common spectacle lens types

Answer 11

single vision (SV) eg sphero-cyl
bifocal (Bif)
varifocal (PAL, PPL)
lentrifocal (lentic), uncommon
trifocal (Trif), uncommon
Prisms: may be present on any type of lens

Question 12

Single Vision

Answer 12

pre-presbyopes
only one power
only one distance in focus for presbyopes: reading, intermediates or distance
simplest form of spectacle correction: available in most prescription types

Question 13

Prisms

Answer 13

• lenses thicker at one edge than other, not looking through optical centre
• thick edge goes on opposite side to direction eye turned or opposite direction it wants to turn in ‘phorias
• correcting way light travels through eye not eye squints etc

Question 14

Bifocal

Answer 14

used by presbyopes
2 lens powers so 2 distances
line shows patient’s age
things jump- get double vision as eyes cross distance-near

Question 15

Varifocal

Answer 15

usual prebyopia solution
range of powers over lens- distance, near & intermediate
no line
no jump or double vision
distortion and blur

Question 16

Lentricular

Answer 16

v high powers

only really used when no other solution

Question 17

Trifocal (etc)

Answer 17

3 near areas (trifocal)
usually disrance-intermediate, near
unusual in uk

4 reading areas (quadrifocal)
almost unknown in uk
similiar problems to bifocals