Eye conditions and case studies
Presented on 28 October 2011
Dr Andrew Blaikie
Consultant Ophthalmologist
Management of Childhood Visual Impairment
Normal brain growth The last 3-4 months of gestation
- Critically important in the normal development of the nervous system
- The 'flowering' of the dendritic tree occurs during this period
1011 neurons
100,000,000,000,000
3 months is equal to
- 12 weeks
- 84 days
- 2016 hours
- 120 960 minutes
- 7,257,600 seconds
100,000,000,000,000 synapses divided by 7,257,600 seconds means that ...
Every second 14 million synapses are being created
Premature brain vulnerable to injury for several reasons
- Immature blood supply; leads to ischaemic 'end zones' in the deep periventricular white matter
- Immature autoregulatory mechanisms; lead to ischaemic and haemorrhagic damage
- Immature glial cells; selectively vulnerable to hypoxic/ischaemic injury
- Free iron (from bleeding); increases sensitivity of glial cells to free radical injury
Typical features of ex-premature neonate brain include reduced;
- Grey and white matter volume (focal and diffuse peri-ventricular loss)
- Cortical folding
- Size of the corpus callosum (posterior)
- Size of the thalamus (sometimes with abnormal signal)
More ex-premature neonates; More children with disability
- Improvements in obstetric and neonatal care has led to improvements in the chance of surviving premature birth
- This has also led however to more children surviving with neurological impairment
There are two separate functional streams of visual information that complement each other creating the overall sense of vision – the 'where' and the 'what' streams
The 'process' of vision
- Survey the overall scene
- Locate and attend to one object amongst many
- 'Recognise' this object
- Decide on an appropriate plan of action
Visual Attention
Important but poorly recognised
Attention: An important but forgotten about (unrecognised?) aspect of visual function
- Attention is a well recognised aspect of visual function in the visual science literature but not in the ophthalmic (eye doc) literature.
- Over 2000 hits on medline
Ex-premature neonates are particularly susceptible to problems with visual attention
- Posterior parietal lobes often affected by PVL
- Thalamus typically reduced in size
Both areas are key parts in the process of creating attention.
Natural everyday visual scenes are complex and cluttered and consequently problems with visual attention lead to problems in these kinds of situations...
The principles of managing dorsal stream dysfunction are:
Generally minimising background visual and auditory distracters,
Limiting the amount to see at any one time,
Storing stuff routinely and systematically to limit the need to 'search'.
Importance of the optical management
- Poor emmetropisation
- Impaired Accommodation
- Brain injury and anti-cholinergics
Impaired accommodation
Common in:
- Cerebral Palsy
- Down's syndrome
Watch out for hyoscine patches and baclofen pumps
- Absent
- Slow
- Inaccurate
- Easily fatigued
- Unstable
Therefore some children may benefit from bifocal glasses. And again they need to be 'set' correctly (fitted by a qualified dispensing optician).
Bifocal fit even trickier. I tend to prescribe two separate sets of glasses: Near and Distance 'sphere'
Conclusions
- Disabilities due to CVI can be obscure, and are often missed
- Yet the resultant problems may be very disabling and frustrating in all aspects of life
- Recognition and (re)habilitation for this common disorder are essential to prevent long term educational and social disadvantage of affected children (and adults)
If you are working with children (and adults) with CVI you need to have a practical working knowledge of how the brain creates vision
- to allow you to understand how they might see the world
- to help you create strategies to help them.