Orthoptics I - normal visual development and emmetropisation

Describe the structure of the eye at BIRTH?

blueish irises, poor dilation, lens nearly spherical, under-developed retina, axial length of 16-17 mm, mainly rod cells present

Describe the eye structure at 2 MONTHS?

ciliary muscles stronger to allow focussing, cone cells developing

Describe the eye structure at 6 MONTHS?

CCT ~1.48 mm
PCT ~ 1.2 mm

At what age is the macula mature?

8 months old

What is the average axial length at 12 MONTHS?

20-21 mm

What is the average axial length of an ADOLESCENT?

23-25 mm

If the infant is not visually responsive by which age will they be referred?

8 weeks

At what age will an infant fix and follow a light?

~3 months

Describe the eye functionality between BIRTH and 1 MONTH

blinks in response to bright light
unco-ordinated eye movements
staring at objects 8-10 inches away
stare at light or face (recognition, not detection)
begins to track movement

Describe the eye functionality between 1 and 2 MONTHS

clear vision for 10-12 inches
stares at faces and black and white images
follow an object up to 90degs
watches parent closely
begins to develop tears (too much is a sign of blockage)

Describe eye functionality at 2 to 3 MONTHS

this is where they actually start to see
begin to notice familiar objects for up to 12 inches
examines own hand
following faces, lights and objects

Describe eye functionality at 4-5 MONTHS

beginning of stereopsis - reaching for nearby objects
can identify themselves in a mirror

Describe eye functionality at 5-7 MONTHS

full colour vision
clear vision of a few feet
turns head to view objects
will favour certain colours
touches mirror image of self

Describe eye functionality at 7-12 MONTHS

independent eye movements
seeing smaller objects
depth perception developed
crawling to reach distance objects
playing peek-a-boo
watches and follows fast moving objects

Describe eye functionality at 12-18 MONTHS

clear distance vision
depth perception for objects further than 2 feet away
refined eye movements
recognizes images of familiar objects
walks to interact with interesting items
recognizes themselves in a mirror

Describe eye functionality at 18-24 MONTHS

begins to focus on objects closer than 2 feet
clear distance vision
development of fine motor skills
colouring
identification of body parts

Describe eye functionality 24-36 MONTHS

convergence and accommodation improved
BSV at all distances
improved stereopsis
recognizes shapes and objects

Describe eye functionality at 36-48 MONTHS

distance vision should be nearing 0.00
clear single vision a few inches away from face
gross motor co-ordination
recognizes complex visual shapes and letters
colour identification

Describe eye functionality at 48-72 MONTHS

knows letters and some words - recognizing orientation
beginning to read
matured stereopsis
clear, single and comfortable vision at all distances

Describe accommodation

process in which the eye changes optical power
- requires convergence
- can be consciously controlled

What are the 4 common refractive errors?

hyperopia
myopia
astigmatism
presbyopia

What is a subjective refraction?

reading the chart at the optician - telling the examiner what you can and cannot see

What is cycloplegic refraction?

requires pupil dilation to paralyze the lens
light refraction at the fovea is checked by adding various lenses in front of the eye

Describe hyperopia/hypermetropia

distance objects clear, whilst near object blurred
due to insufficient accommodation, flat cornea or a flat lens
light rays converge AFTER the retina

Describe myopia

distance objects blurred, near objects clear
light rays converge BEFORE the retina
long axial length
increased myopia = increased risk of retinal detachement

Describe emmetropia

a distance object at optical infinity is in focus with the lens in a neutral state

What is the process of emmetropisation?

process by which the refraction of the anterior chamber and the axial length of the eye balance each other out
- guided by visual input
- assumed to be an active mechanism

What factors affect normal emmetropisation?

near activities - myopia progression
strabismus - link between accommodative esotropia and hypermetropia

What is the average refractive state between 3 - 9 months?

wide range of refractive error
on average improves with decrease SD

What is the average refractive state between 1 - 3 years?

further shift towards emmetropia
decreased refractive variability
improved standard deviation

What is the average refractive state after 6 years?

differs per population but majority have no refractive error after this age