Orthoptics I - Visual Acuity

VA at full term

1-2/60

VA at 0 - 6 months

0.5 - 0.3 logMAR

VA at 18 months

0.3 - 0.2 logMAR

VA at 2 to 3 years

0.2 - 0.0 logMAR

VA after 4 years

0.0 logMAR

What are the features of a clinical vision assessment?

age-dependent test
testing threshold vision
involved optotype recognition

Age appropriate vision test for babies

visual behaviours
forced choice preferential looking
teller acuity cards
cardiff cards

Age appropriate vision test for 18 months - 3 years

Kays pictures
letter chart

List some near visual acuity tests

Maclure
Jaeger
Nieden
reduced Snellen
reduced logMAR

What is visual crowding?

occurs when objects that can be perceived in isolation become difficult to recognise in clutter
= reliance on rod cells in the periphery - orientation difficult to determine

What are some disadvantages of Snellen charts?

irregular steps between lines
no. of letters per line varies
spacing dictated by available space
some letters more recognizable than others
irregular shape of chart

What are some advantages of EDTRS/logMAR charts?

steps between lines are equal
all lines have 5 letters
spacing equal to letter size (equal relative crowding)
letter recognition difficulty balanced per line

Describe the ATS protocol

uses single optotypes in a box for a crowding effect

What is "low vision" defined as?

significant visual impairment which cannot be fully corrected by:
- glasses
- contact lenses
- medication
- surgery

Causes of "low vision"

macula degeneration
diabetic retinopathy
glaucoma
retinitis pigmentosa
trauma
anatomical abnormalities