Abnormal visual development Flashcards
Mechanism of development, significance 2 and treatment of myelinated nerve fibres
- <1% of ppn has it
- Ogliodendrocytes produce myelin in the opp direction from optic tract towards globe hence is most often seen at ONH
- Often benign but can be associated with strabismus, myopia and amblyopia
- Treatment not required
Mechanism of development 5, significance 2, treatment 4 of congenital cataract
- Occurs after 33 days gestation
- Idiopathic
- Metabolic disorders
- Infection: rubella, toxoplosmosis
- Gene defect: crystallin encoding genes - altered characteristics make it insoluble, lens specific connexins - important at maintaining gap junctions in avascular lens
- Leading cause of reversible congenital blindness in children: 1-15/10,000 live births
- Possibility of FD amblyopia due to the clouding of the lens
- Treat with cls, surgery, patching (1hr/day for 6 yrs but disapproved as it was too distressing or amblyopia was too dense to be reversed by patching)
- Majority of children will not achieve greater than a VA of 0.6logMAR in the affected eye
What 2, prevalence 1 and significance 3 of persistent hyaloid artery
- Remnant of hyaloid artery that should degenerate by 7th month
- Viewed via Ophthalmoscopy
- 95% of premature infants have it
- Benign but can cause VF defects or seen as floaters as vitreous liquefies where it then casts a shadow
What 4, genes 3, significance 4, treatment 2 of coloboma
- Due to the incomplete closure of choroidal fissure that corresponds to the ocular structure that did not develop properly eg ON, retina, eyelid
- Should close by day 37
- Usually unilateral
- 1 in 10,000
- Genes: GDF3, VSX, SHH
- Associated with microphthalmia
- Can cause a VF defect if retina/ON coloboma
- Anterior colobomas - increase glare and light sensitivity
- Ask px to look up as it is usually inferior (where choroidal fissure used to be)
- Treat with opaque cls for anterior (risk of hypercapnia) and no cure for VF defect
What 3, signs 2, symptoms 4, treatment 2 of congenital glaucoma
- Abnormality of AH drainage
- 1 in 10,000 live births
- Theorised to be due to an atrophy of the visual pathway that has retrograded onto the VF
- Optic atrophy in severe cases, buphthalmos or macrophthalmos
- Hazy cornea
- Tears and closes eyes frequently
- Photophobia - possibly seen as dysfunction of corneal endo
- Bilateral surgery to increase AH drainage or remove ciliary processes
- Eye drops
What, cause, timing and treatment 3 of macrophthalmos
- Abnormally large eyes
- Most of the eye size grows within the first year, 70% of the globe’s volume by 4yo, 90% by 70yo. Growth of eye ends at 14yo, growth of orbit ends at 11yo for F and 14yo for M
- Surgery preserves vestigial tissue (development of one leads to development of another)
- Important to commence early in life
- Expanding implants that progressively increase in size are given to encourage growth
What, prevalence, cause 3 of microphthalmos
- Abnormally small eye
- 1 in 10,000
- Genes or chromosomal defect
- Environmental factors: rubella infection, teratogen exposure, radiation
- Can be formed by itself or in part with a syndrome eg coloboma
What, prevalence, timing and treatment of ankyleblepharon
- Eyelids fail to separate
- Very rare
- Should separate by week 20
- Blepharoplasty
What, cause, treatment of blepharonphimosis
- Horizontal aperture is smaller than normal due to incomplete separation
- FOXL2 gene mutation
- Blepharoplasty
What, prevalence, cause 2, significance 2 of anophthalmos
- Complete absence of eye
- Very rare
- Genetic or chromosome mutation
- Infection eg rubella or toxoplosmosis
- Blind
- May be related to carnio-facial abnormalities
What, prevalence, significance 2 of cilio-retinal artery
- Extra choroidal vessel that has emerged through ON
- Very rare
- Benign
- Beneficial as an extra source of blood supply
What, significance 2 of physiological swelling of ONH
- Common in hyperopia due to small eye
- VF defect confirms that it is not a normal variation
- The same number of ganglion cells and axons will be squeezed through ON
What and significance of physiological cupping
- Cup is abnormally large thus C:D ratio is high
- Myopic elongation will stretch it out to make it seem more spread out
Define teratology
Study of abnormal development of embryos and the causes of congenital malformations or birth defects
What is a miscarriage?
Miscarriage is when the body stops developing the foetus due to too many abnormal chromosomes. If teratogen is active within the first 2 weeks of gestation, then death of embryo will occur
Significance of teratogen activity 3
- If active from day 15 to 8th week gestation –> abnormal structure and function
- Embryo is the most susceptible to congenital abnormalities as it undergoes rapid differentiation
- Critical period for brain development is 3-16wks
What did Till 2005 do 2 and find 4 about prenatal exposure to toxic substances?
- 21 exposed mum infants (from occupational radiation) and 27 non-exposed infants
- CS and grating acuity with sweep VEP
- Chromatic and achromatic (luminance) systems with transient VEP
- Log CS low in both groups
- B/Y system no difference
- R/G system VEP more abnormal in exposed group
- VA poorer in high exposure group
- Mothers should work elsewhere or do another job
Significance of foetal mercury neurotoxicity and symptoms 4
- Mercury bioaccumulates in the aquatic food chain
- Highest: Mackerel king, sword fish, shark
- Lowest: tuna, salmon, scallop, shrimp
- Symptoms are dose-dependent
- Ataxia: uncoordinated movement
- Auditory problems
- Abnormalities with VF and CV as mercury tends to attack PR outer segments
- Low IQ and performance in tests - memory, attention
Describe congenital rubella syndrome as an infectious disease
- Rubella virus can be transferred to foetus via placenta
- Mother most susceptible to infections during first 10 weeks and final month of pregnancy
- Virus can cause still birth, abortion and severe foetal malformations
- Earlier onset = greater malformations
- Chorioretinitis (salt and pepper fundus)
- Cataract
- Cardiac malformations
Describe congenital Zika syndrome as an infectious disease
- If pregnant mother has Zika virus, it may lead to microencephaly in their unborn child
- 100% will have visual impairment
- 40% will show ocular abnormalities (nystagmus, strabismus)
- 60% will show cortical visual impairment
- Small head and intellectual disability
What, prevalence, phenotypic characteristics 5, possible mechanisms 7 for ocular abnormalities of down syndrome
- DS have an extra chromosome, 47 instead of 46
- 700-900 babies with a chromosomal disorder are born worldwide
- Heart defects in 50%
- Retardation of growth and development
- Flattened face, upward eye slant
- Premature aging: early onset of Alzheimers disease, life expectancy 60yr
- Ocular abnormalities: RE (due to incomplete emmetropisation, commonly oblique astigmatism), strabismus (commonly esotropia) –> amblyopia may occur if not corrected early on
- Visual cortex and cerebellum abnormalities
- 14-24WG, visual cortex similar
- 40WG, normal controls have more ordered cells
1. abnormal layers in visual cortex
2. decrease dendritic spines and connections
3. decrease brain SA
4. increase gyrus thickness
Inheritance, prevalence, mechanism, significance of fragile X syndrome
- Recently described X-linked abnormality
- 1 in 4,000 males
- Defect of the FMR1 gene –> not making the protein fragile X which is important for NS –> intellectual disability and physical abnormalities
- Poorly understood visual abnormalities: strabismus and RE
Prevalence, disability 2, hypothesis about visual abnormalities 4 and the controversial statement about autism onset
- Different spatial vision processing (weak central coherence hypothesis WCC 4, enhanced perceptual functioning model EPFM, orientation identification task)
- 10-15/10,000 people worldwide
- Restricted behaviours and interests
- Deficits in social communication and interaction
- Deficits in neural pathway that recognises faces and facial expression –> poor social interaction (superior temporal sulcus STS, amygdala, fusiform gyrus) - evident but poorly understood
- Incomplete connections between different brain regions eg between sound and vision –> social and language deficits
- Have the same flicker sensitivity when matched with age-norms –> intact motion processing pathway
- Different spatial vision processing
a. Weak central coherence hypothesis WCC: dysfunction of large-scale neuro-integrative mechanisms results in decreased global perception of local and detailed processes
Evidence:
- less precise temporal processing observed with increasing stimulus complexity
- speech-deficit seen in multisensory temporal processing –> low level deficits may cascade to higher order domains such as language and communication
Anatomical evidence
- brain pruning scans show enlarged grey matter in frontal and temporal (social, emotional, face and object recognition) lobes compared to age-matched norms
- normal grey matter in parietal and occipital lobes –> 1 in 10 have extraordinary talents
b. Enhanced perceptual functioning model EPFM: over-functioning of lower-level perceptual mechanisms lead to enhanced extraction of elementary visual and auditory information
c. orientation identification task: poorer performance when more extensive neural processing is required
- MRR vaccine for measles
What, prevalence 2 of strabismus
- Misalignment of the eyes when they are both open
- 2-4% of caucasians (exo 3x> eso)
- 1% of East-asians (exo>eso)
What did Aurell 1990 and Macoconachie 2013 find out about strabismus?
- Longitudinal study and found that 18% of 34 infants who had a parent with estropia strabismus, will have intermittent or constant esotropia strabismus by 6 months –> flawed as the types of ppl varied and there was not consideration for environmental factor
- Found a higher concordance rate with those who had strabismus in monozygotic over dizygotic twins –> genetic predisposition –> still inconclusive
4 possible mechanisms for strabismus
- Disease of EOM
- Misrouted motor nerves to the EOM
- Defective fusion area
- Defective location for EOM pulleys
What, mechanism, treatment 3 of retinopathy of prematurity
- Abnormal bv growth as retinal vascularisation ends at 22wks instead of 40wks gestation –> angiogenesis or extension of existing bvs coordinated by proliferation and migration of endo cells along VEGF gradient
- Reduced GFs from placental circulation –> delayed retinal vascular development –> avascular areas at the retina which can become hypoxic once in room air –> stimulates angiogenic factors –> vasoproliferation –> can attach to lens and zonules –> contraction leads to retinal detachment
Treatment
- Remove angiogenic factor by burning areas around hypoxic retina (hopefully its far in periphery so it doesn’t impact VA)
- Anti-VEGF therapy: controversial as still young
- Supplemental oxygen: controversial as still young and complications - only given if there is >50% chance of it happening
