1. By Prof Dr. Soheir helmy

2. OUTER layer (protective) Middle layer (nutritive) iris cilliary body choroid Inner layer (retina-photosensetive)

4. It is the innermost layer of the eyeball. Histologically Histologically it is formed of 10 layers.Physiological:- layer of pigmented cells layer of rods & cones {photoreceptors} layer of bipolar cells. layer of ganglion cells.

5. /

6. 1)the retinal pigmented epithelium :- Functions:- 1- contain pigments which absorb light and prevent its reflection inside the eye. 2-store large amount of vit. A 3- phagocytosis of old rods and cones. 4-produce sticky extracellular matrix

7. A photoreceptor cell is a specialized type of neuron found in the retina that is capable of photo transduction. they convert light (visible electromagnetic radiation) into signals that can stimulate biological processes.there are two types of photoreceptors:- Rods cones

8. Rodscones Number120 million8 million SitePeripheral part of the retina Central part of the retina Connection Function PigmentRhodopsinIodopesin Time of visionDarklight

9. It is composed of :- 1-Outer segment 2-Inner segment 3- synaptic part The outer segment consists of a stack of discs embedded in the cell membrane. The photoreceptor's light-sensitive pigments are located on these discs. (rhodopsin) rods have a long, cylindrical, outer segment with many discs while cones have a short, tapering outer segment with relatively few discs.

11. Each disk contains:- 1- photopigment (rhodopsin) 2- G protien transducin 3-CGMP phpspho diesterase enzyme

13. In the dark: receptor potential equals -40 mv Dark current Unstimulated (in the dark), cyclic-nucleotide gated channels in the outer segment are open because cyclic GMP (cGMP) is bound to them.cyclic GMP positively charged ions sodium ions) enter the photoreceptor, depolarizing it to about −40 mV (resting )sodiumionsdepolarizingresting in other nerve cells is usually −70 mV). This depolarizing current is often known as dark current.current

16. 1-When light hits a photoreceptive pigment within the photoreceptor cell.2- The pigment, called iodopsin or rhodopsin, consists of large proteins called opsin and retinal (a derivative of vitamin A). 3-The retinal. activate a regulatory protein called transducin which leads to the activation of cGMP phosphodiesterase,cGMP phosphodiesterase which breaks cGMP allows the ion channels to close, preventing the influx of positive ions, hyperpolarizing the cell, and stopping the release of neurotransmitters

17. 1- optic disc ( blind spot 1- optic disc ( blind spot ) 2-fovea centralis 3- extra foveal area

18. it is slight medial to posterior of the globe. No rods or cons >>>not sensitive to light. It is the optic nerve head Blood vessels enter & leave the eye at this point. Overlap of two visual field>>cannot notice it

21. It is the area of acute vision. It contains only cones. All retinal layers are pulled aside to allow light to fall directly on the receptors.

27. Light reflects on an object,and if one is looking at the object- it enters the eye. Light rays pass through the cornea, aqueous humor, lens, and vitreous humor. All these structure reflect the light that it falls on the retina. This is called focusing. Maximum focusing is done by the cornea and the lens.