Refractive Errors

Question 1

What is acuity measured in

Answer 1

Dioptres

Question 2

What refractors of light does the eye have + what are their strengths

Answer 2

cornea - 40D

lens - 20D

Question 3

What is emmetropic vision

Answer 3

Perfect vision - 60D refraction + 22.22mm axial length

Question 4

what is myopia and how is it fixed

Answer 4

short sightedness - due to focal point being in front of the retina - fixed with a concave lens

Question 5

what is hypermetropia and how is it fixed

Answer 5

long sightedness - due to focal point being behind the retina - fixed with the convex lens

Question 6

What does a visual assessment consist of

Answer 6

distance vision
retinoscopy 
subjective refraction 
near vision assessment 
unit magnification

Question 7

what are measurers of acuity

Answer 7

LogMAR

Snellen charts

Question 8

what is the best measurer of acuity + why

Answer 8

logMAR - equal number of letters all the way down

Question 9

what is a refractive error called

Answer 9

ametropia

Question 10

what are 2 main causes of ametropia

Answer 10

axial - where the axial length changes

refractive ametropia - changes in refractive index

Question 11

what is an astigmatism

Answer 11

asymmetrical eye shape, leading to bent light rays, leading to 2 points of focus on retina

Question 12

how do you fix an astigmatism

Answer 12

toric and cylindrical lenses

Question 13

what is presbyopia

Answer 13

loss of accommodation, corrected by +ve lenses

Question 14

what are visual indications for contact lenses

Answer 14

anisometropia (unequal refractive powers)
high myopia
aphakia - absence of lens due to surgery (congenital cataracts)
irregular cornea
refractive surgery failure

Question 15

what are occupational indications for contact lenses

Answer 15

theatre
film
armed forces
sports

Question 16

what are requirements for contact lenses

Answer 16

stable, accurate visual acuity
good comfort throughout wear
easy to insert/remove
easy to clean/replace/reproduce 
reasonable cost
maintain corneal physiology
minimal lid/teat film inteference

Question 17

what needs assessing before contact lenses

Answer 17

prescription + patient needs
keratometry performed - any astigmatism identified
slit lamp assessment - corneal health, lids and tear film
Trial lens fitted

Question 18

what is contact lens aftercare

Answer 18

correct cleaing/insertion/removal
gradual build up to every day wear
1 month of wear -> aftercare appointment (check refraction, fit and eye health)
repeat 3 months and 6 months then annually

Question 19

what are complications of contact lenses

Answer 19

giant papillary conjunctivitis 
corneal abrasion 
infecting keratitis
corneal ulcers
neovascularisation 
corneal hypoxia
solution hypersensitivity

Question 20

what types of contact lenses are there

Answer 20

soft

rigid-gas-permeable

Question 21

what are the advantages and disadvantages of soft contact lenses

Answer 21

Adv - flexible, good confort, good VA, large diameter so its a safer sit, safer for sport, easier to fit, suitable for extended wear

Disadv- split, tear deposition, expensive, can dehydrate

Question 22

what are advantages and disadvantages of rigid-gas-permeable lenses

Answer 22

Adv - fixed shape, durable, easy to clean, good for all day wear, decreased diameter = less likely for hypoxia, smooth surface = better visual result for irregular corneas and high astigmatism

Disadv - poor initial comfort, small diameter, more prone to falling out