Physiology of Vision By Dr Abdel Aziz M
Physiology of Vision By Dr. Abdel Aziz M. Hussein Lecturer of Physiology Member of American Society of Physiology
The Retina • The retina is the innermost photosensitive layer of the eyeball. • It contains about 55 types of cells and 70% of total sensory receptors • Histologically, it is formed of 10 layers • Physiologically, 4 layers have special importance
The Retina
The Retina
Functional Layers Pigmented Epithelium Photoreceptors Bipolar cells Ganglion cells
Pigmented Epithelium
Contains large amounts of melanin pigments
Produces a sticky ECF matrix
continual renewal of the outer segment of the rods and cones.
Breakdown and Resynthesis of the Photopigments
Stores Large Amount of Vit. A
Photoreceptor Layer
Rods and Cones
Outer Segment
Outer Segment
Inner Segment Outer segment Inner segment
Rods and Cones Rod 120 millions Rod One pigment (rhodopsin) Cones 7 millions Cone 3 pigments (iodopsin)
Distribution of Rods and Cones cones are central Rods are peripheral
Rods and Cones Convergence
Rods and Cones Functions Rod Cone more sensitive to light less sensitive to light Less accurate more accurate Cannot perceive colours Can perceive colours Night vision Day vision
Ganglion and Bipolar cells
Rods and Cones Convergence Bipolar cells 1 st order neuron Ganglion cells 2 nd order neuron
Lateral Cells
Blood Supply of the Retina
Blood Supply to the Retina Central retinal artery Supply inner layer of retina Choroidal blood vessels Supply pigmented epithelium and photoreceptors
Blood Supply to the Retinal detachment (occurs between the pigmented epithelium and photoreceptors) In this case the retina can resist degeneration for days due to its own blood supply (from central retinal artery) and diffusion of fluids across the detachment gap. If the retina is not replaced rapidly within few days degeneration of the retina occurs.
Retinal Detachment
Special Areas of the Retina
Special Areas of the Retina • Fundus oculi is the part of the retina which can be seen by ophthalmoscope. Fovea centralis Optic disc
Fovea Centralis Fovea centralis
Phototransduction
Phototransduction 1. Decomposition of photosensitive pigment in rods & cones 2. Excitation of the photoreceptors by activated rhodopsin and generation of photoreceptor potential 3. Termination of excitation 4. Regeneration of photopigments
Decomposition of Pigment
Photoreceptor Potential In Dark
Photoreceptor Potential In Light
Termination of Excitation • Within a sec the activated rhodopsin is inactivated by the enzyme rhodopsin kinase
Regeneration of Pigment
Summary of Generation of Photoreceptor Potential
THANKS
- Slides: 45