Physiology Flashcards
Absorption spectrum of rhodopsin
498nm
Absorption spectrum of red opsin
564nm
Absorption spectrum of green opsin
534nm
Absorption spectrum of blue opsin
420nm
Absorption spectrum of melanopsin
480nm
What type of protein are opsins?
G protein coupled receptors
What is the visual cycle?
Regeneration of 11-cis-retinal after its conversion to all-trans retinal on exposure to light
What triggers the shedding of rod and cone outer segments respectively?
Rod OS - shed at first light
Cone OS - shed at darkness
State in brief the steps in the visual cycle.
- Rhodopsin –> light –> Opsin + all-trans-retinal
- All-trans-retinal complexes with lipoprotein and is transported into rod cytoplasm by ABCR
- All-trans-retinal in rod cytoplasm –> retinol dehydrogenase –> oxidised to all-trans-retinol
- All-trans-retinol is transported into RPE by IRBP
- All-trans-retinol complexes to CRBP –> transferred to LRAT which stores it as all-trans-retinyl esters
- All-trans-retinyl esters –> RPE65 –> 11-cis-retinol
- 11-cis-retinol complexes to CRALBP –> transferred to retinol dehydrogenase which reduces it to 11-cis-retinal
- 11-cis-retinal is transported back into cones by IRBP and combines with opsin to regenerate rhodopsin
Visual cycle protein implicated in Stargardt’s disease + mode of inheritance
ABCR, autosomal recessive.
Retinal-lipid complexes are not transported from the rod membrane discs into the cytoplasm –> accumulate in RPE cells after phagocytosis –> toxic to RPE
Visual cycle protein implicated in retinitis pigmentosa and Leber’s congenital amaurosis
RPE65 -accounts for 2% of retinitis pigmentosa spectrum and 16% of LCA spectrum. Autosomal recessive
What is the volume of aqueous humour in the eye? What is the rate of secretion of aqueous humour?
How long does it take for the aqueous humour to be completely replaced?
Normal vol. = 250ul in anterior chamber
Normal rate of secretion = 2.5ul / min
Hence, normal turnover = every 100 minutes
What is the blood supply of the ciliary body?
Ophthalmic artery –> long post. and ant. ciliary arteries –> Major arterial circle –> supplies the highly vascular nonfenenstrated capillaries ciliary stroma
What are the components that make up the blood-aqueous barrier?
Non-fenestrated capillaries in the iris stroma
Tight junctions in the ciliary epithelium (nonpigmented epithelium)
What is the main GAG in the corneal stroma?
Keratan sulphate
What is the main collagen in the corneal stroma?
Type 1 / Type 5
What are the factors that:
a) tend to cause corneal hydration
b) tend to cause corneal dehydration?
Corneal hydration: - Imbibition pressure - Intraocular pressure Corneal dehydration: - Endothelial cell pump - Epithelial cell pump - Tear film evaporatioin
What are the organisms that can penetrate an intact corneal epithelium?
CHNLS
Corynebacterium Haemophilus influenzae Neisseria meningitides / gonorrhoeae Listeria Shigella
What are some drugs that cause drug-induced keratopathy?
Amiodarone
Indomethacin
Tamoxifen
At what age does the human eye usually stop growing?
Age 7-10
Axial length is 17mm at birth and 25mm in the adult
What is the rate of basal tear production?
1.2ul/min
What chromosome and arm is the HLA gene complex located on?
6p21
