Blind spot of mariotte ?
Ans. is 'b i.e., Optic disc Posterior pole of retina has two distinct areas :- Optic disc (optic nerve head) : It is a veically oval area, with average dimension of 1.76 mm horizontally and 1.88 mm veically. The optic disc is placed 3-4 mm nasal to the fovea (fovea is temporal to optic disc). There is a central depression in the optic disc called physiological cup. There are no light sensitive rods or cones to respond to a light stimulus. Therefore, it causes a break in the visual field called the blind spot or physiological blind spot which is presented as physiological absolute scotoma on visual field chaing. Optic disc is the location where ganglionic cells axons exit the eye to form the optic nerve and optic disc represents the beginning of the optic nerve. The optic nerve head (optic disc) in a normal human eye carries 1-1.2 million neurons from the eye towards the brain. The optic disc is also the entry point for the major blood vessels (CRA & CRV) that supply the retina. CRA and CRV emerge through the physiological cup. Macula lutea (yellow spot) Macula lutea is a small yellowish area 5.5 mm in diameter, situated at the posterior pole of the eyeball, temporal to the optic disc. Fovea centralis is the central depressed pa of the macula and has a diameter of 1.5 mm. It is situated about 2 Disc diameter (3 mm) temporal to the temporal margin of optic disc. It is the most sensitive pa of retina, with lowest threshold for light and highest visual acuity because it contains only cones. Following pas are related to fovea centralis :? Foveola :- Forms the central floor of the fovea (0.35 mm in diameter). Actually, it is foveola which is situated 2 Disc diameter (3 mm) temporal to temporal margin of the disc Umbo Is a tiny depression in the very centre of foveola. Foveal avascular zone (FAZ) :- It is located inside the fovea but outside the foveola. It is an area about 0.8 mm in diameter (including foveola and some surrounding area) which does not contain any retinal capillaries
Fovea centralis
Optic disc
Macula lutea
Ora serrata