Normal Visual Development

Question 1

When does the visual cortex respond to visual stimuli?

Answer 1

Electrophysiological studies suggest visual cortex responds to visual stimuli as early as 30WG - corresponds with eyelid separation. Functional but still poor

Question 2

Describe accommodation development

Answer 2

• Can from at least 1 month

- Accuracy 2-3mths

Question 3

When does vernier and grating acuities develop by?

Answer 3

Grating - plateaus after 6 years

Vernier - continues till 14 years

Question 4

Compare the 5 types of letter acuity charts (Keeler logMAR, HOTV, Kay Pictures, Lea Symbols, ETDRS) in regards to number of optotypes, spacing, acuities measurable at 3m and chart. Which type of chart should be used? Compare between Kay Picture and Landolt C

Answer 4

0. 8 to -0.3
1. 7 to -0.3
2. 0 to -0.1
3. 6 to -0.1
4. 0 to -0.3

Question 5

Contour integration and D value

Name of the stimulus

Answer 5

o A closed contour embedded in noise eg Gabor patch-defined circle and square contours in different noise densities
o Note that the contour is no longer apparent when the elements are dots
o D: is the relative density of elements as a ratio of noise element spacing over contour element spacing  higher D value indicates easier visibility (widely spaced noise elements; more closely spaced contour elements)
o In children, threshold depends on spacing of the contour elements  this suggests that children have a poorer ability to integrate those elements over space
 Contours can be detected and meaning ascribed to the forms, created by the contours, is present at 6mths but not at high levels of noise
 Due to immaturity of horizontal connections between cells responsive to different visual field regions

Question 6

What do EOG, ERG and VEPs measure?

Answer 6

EOG - health of retina and RPE
ERG - function of retina
VEP - retina to visual cortex

Question 7

What does it mean by preferential stimulus?

Answer 7

Rods: slow flash stimulus, dim red, 501nm, scotopic background
Cones: 30Hz flash stimulus, 560nm tennis ball yellow, photopic background

Question 8

What are the 6 ISCEV standardised ERG protocols? Why were they created?

Answer 8

DA 0.01 - rod driven - ON BC
DA 3 - combined (rod dominated) - PRs and BCs
DA 10 - combined with enhanced a waves - reflect PR function
DA OPs - amacrine cells
LA 3 - cone system and LA 130 - sensitive to cones - a waves from cones PR and OFF BC, b waves from ON and OFF cone BCs