BIOSYSTEMS: SEMINARS - milestones, vessels, cil., iprgc, vis. field Flashcards
Summarise the development of the eye following closure of neural tube [ocular milestones #1]
wk 4: closure of neural tube (start); formation of optic vesicles + lens placode (end)
wk 5: formation of lens vesicle + optic cup (start)
wk 6:development of primary lens fibres + optic nerve (start)
wk 7: establishment of hyaloid artery + completion of closure of choroidal fissure (at start)
wk 7-8: migration of precursor cells to primitive neural retina
*tube - placode - vesicles - cup - fibres - nerve - hyaloid - fissure closure - migration precursor cells
What is coloboma? [ocular milestones #2]
- a congenital defect of the eye that occurs due to incomplete closure of the choroidal fissure
Which structures are affected by coloboma? [ocular milestones #2]
Depends on which part of choroidal fissure doesn’t close properly.
If anterior: cornea, iris, ciliary body, lens
if posterior: choroid, retina, optic nerve
What does a coloboma-affected iris look like? [ocular milestones #3]
Characteristic keyhole pupil in inferior region
When does fusion of coloboma start? [ocular milestones #2]
At around week 5 (fusion starts centrally and proceeds outwardly), complete by week 7
List 3 subtypes of coloboma by the structure they affect. [ocular milestones #2]
- Iris coloboma
- Chorioretinal coloboma
- Optic nerve coloboma
What does complete iris coloboma affect? What about partial? [ocular milestones #2]
Complete: affects pigmented epithelium (PE) + stroma
Partial: only affects pupillary margin (only oval-pupil, not keyhole)
When does chorioretinal colboma and what does it affect? [ocular milestones #2]
When posterior part of choroidal fissure won’t close properly.
Affects: RPE, retina, choroid
(also increases risk of retinal detachment)
How does optic nerve coloboma affect the NRR? (ocular milestones #3]
Thinning and absence of NRR in infero-nasal portion
Causes of coloboma? [ocular milestones #2]
Inherited: mendelian (AD, AR, or X) or chromosomal abberations (often with co-morbidities)
Environmental:
- drug use (thalidomide)
- alcohol (foetal alcohol syndrome)
- Vitamin A deficiency
What is Microphthalmia and how can coloboma cause it? [ocular milestones #3]
Abnormally small eyes with abnormalities such as turned eye
Cause: failure to close fissure causes vitreal fluid drainage (vitreal fluid needed for eye development)
Why would a left eye be turning in intermittently in 2 year old px? [ocular milestones #3]
May be due to:
- coloboma assoc. microphthalmia
- other unrelated EOM defect
- CN6 defect
- high hyperopia/anisometropia
Why might the red-eye effect be stronger in photographs for one eye in 2 yo px [ocular milestones #3]
May be due to:
- left eye atrophy of posterior structures, assoc. with chorioretinal coloboma
- retinoblastoma (cancer at posterior retina) - can lead to white pupil reflex
- congenital cataract
What clinical observations could you make/check for in a 2yr old px with turned ey intermittently? [ocular milestones #4]
- ask if during specific task
- check for anisometropia
- check for VA (drop in VA with coloboma)
- check for esophoria/tropia (expect large esotropia for coloboma)
- check for CN palsy (in ocular motility)
- check for APD (afferent pupil defect) (for optic nerve coloboma)
- look at back of eye to check for retinoblastoma
What is the normal average size of the optic nerve head? [ocular milestones #4]
About 1.70mm horizontal, 1.90mm vertical
Describe the clinical representation of optic nerve atrophy [ocular milestones #4]
Manifest as:
- change in colour and structure of optic disk
- with variable degree of visual dysfunction
- ONH = pallor apearance
note: glaucoma is a common cause of optic nerve atrophy
Clinical features of optic nerve hypoplasia? [ocular milestones #4]
Abnormally small ONH, gray-pale disc with double peripapillary ring, vascular tortuosity, thinning of RNFL.
Could be assoc. with hypothalamic/pituitary dysfunction
List and describe the 3 layers of blood vessels (ordered from inner to outer layer) [Blood Vessels #1]
- Tunica intima: single layer of fenestrated endothelial cells (has valves to stop back-flow)
- Tunica media: SMCs allowing for vasoconstriction/dilation
- Tunica adventitia: layer of type 1 collagen and fibroblasts for anchoring
Compare the 2 Blood Ocular Barriers: blood aqueous barrier (BAB) and blood retinal barrier (BRB) [Blood Vessels #1]
BAB: formed by an epithelial barrier located in the Non-pigmented ciliary epithelium and posterior iris epithelium
BRB: located at 2 levels:
outer barrier in RPE - restricts molecule passage to outer segment of photoreceptors
inner barrier in endothelial membrane of retinal vessels - for preserving vessel homeostasis
Both: these layers have “leaky” tight junctions
What artery provides blood supply to the eye? What are its main subdivisions/branches? [Blood Vessels #1]
Ophthalmic artery. Is composed of:
- central retinal artery: supply inner retina
- lacrimal artery
- long posterior ciliary arteries: supply iris + cil. body
- short posterior ciliary arteries: form arterioles in choroid (also supply cil. body)
How do the following affect IOP? A: Systolic b.p B: Systemic b.p C: Obesity: D: Glaucoma E: Normal-tension Glaucoma [Blood Vessels #2]
A: Increased systolic b.p – increase IOP via increased capillary pressure within cil. body
B: Increased systemic b.p – affect episcleral venous pressure
C: Obesity correlated with increased IOP
D: Glaucoma – increased IOP via increased blood volume within cil. body
E: NTG - IOP same
What level of Ocular Perfusion Pressure (OPP) is suggested to increase risk of Glaucoma [Blood Vessels #3]
Low OPP
How does our body compensate/counterbalance for low OPP? Can this system be impaired? [Blood Vessels #4]
A drop in OPP is counter-balanced by autoregulation:
- vasodilation (the vessels release NO) + tissue oxygen extraction
- constant BF + oxygen metabolism maintained
- neuronal function is preserved
What are the biochemical effects of low OPP (ocular perfusion pressure)? [Blood Vessels #4]
- mitochondrial dysfunction
- oxidative stress
- glial cell upregulation
All 3 of these things cause ganglion cell damage and apoptosis
