measuring vision and visual acuity

Define vision

the smallest line of letters than can be seen before new refractive error

Define aided vision vision

vision with spectacles or contact lenses

Define unaided vision

without spectacles of contact lenses

Define visual acuity

the smallest line of letters that can be seen with the best possible refractive correction in place

what is average vision

6/6

why do we measure vision

1. legal requirement

2. baseline data

3. diagnostic tool

4. measures progression of disease

5. evaluates treatment

6. patient expectation

minimum angle of resolution (MAR)

the ability to see detail. two distinct points can be distinguished

What is the average minimum angle of resolution

1 min of arc

what are the two types of charts used

snellen a d logmar

what are the advantages of Snellen chart

1. commonly used and recognised

2. easy recording

3. can be portable

what are the disadvantages of snellen chart

1. different numbers of letters on each line

2. unequal size progression

3. less repeatable than LogMAR

4. 1/3 less sensitive than LogMAR

Advantages of logmar

1. same number of letters on each line

2. even line spacing and crowing

3. standardised recording

4. logarithmic progression

5. more repeatable than Snellen

6. more sensitive to interocular differences than Snellen

disadvantages of logmar

1. large not portable

2. less commonly used so less recognizable

3. recording can be trickier initially to interpret