The retina is a thin, light-sensitive layer of tissue located at the back of the eye. It plays a crucial role in the process of vision by capturing light and converting it into electrical signals that are transmitted to the brain for interpretation.
Key features and components of the retina include:
1. Photoreceptor Cells: The retina contains two types of specialized photoreceptor cells, known as rods and cones. Rods are responsible for vision in low-light conditions and are more sensitive to light, while cones are responsible for color vision and visual acuity, functioning best in bright light.
2. Retinal Pigment Epithelium (RPE): The RPE is a layer of cells located between the retina and the choroid, a vascular layer supplying nutrients to the retina. The RPE helps nourish and support the photoreceptor cells, as well as absorbs excess light to prevent reflection and scatter within the eye.
3. Bipolar Cells and Ganglion Cells: Bipolar cells receive electrical signals from the photoreceptor cells and transmit them to the ganglion cells. Ganglion cells then combine and carry these signals from the retina to the brain via the optic nerve.
4. Macula and Fovea: The macula is a small specialized area at the center of the retina, responsible for high-resolution central vision. Within the macula, the fovea is a tiny pit that contains a high concentration of cone cells, providing the sharpest visual acuity.
5. Optic Disc: The optic disc, also known as the blind spot, is a small area where the optic nerve exits the eye. It lacks photoreceptor cells, resulting in no vision at that specific spot.
The retina acts as the initial site of visual processing, converting light into electrical signals that are transmitted to the brain through the optic nerve. Once the electrical signals reach the brain's visual cortex, they are further processed, leading to the perception of visual images.
Various conditions and diseases can affect the retina, such as retinal detachment, diabetic retinopathy, macular degeneration, and retinitis pigmentosa. Regular eye examinations, particularly dilated eye exams, can help detect and manage retinal disorders, preserving vision and ensuring optimal eye health.
4. Retina
The retina is the light- sensitive portion of the eye
Two types of receptors
Rods(dim light vision & black and white vision)
Cones(color vision)
7. Rods and cones from periphery to fovea
In periphery of retina
rods are 2 to 5 micrometers in diameter
cones are 5 to 8 micrometers in diameter
At fovea
No rods
Cones are slender with less/ no fat
18. Dark Adaptation
Initial inc. caused by cones
Rods provide persistent
progressively increasing sensitivity
for hours
Rods synapse with only ganglion
cells and their action potentials
summate and add up to give
persistent increase in sensitivity
19. Cones
The cones are about 30 to 300 times less sensitive than the rods with 4 times
faster initial response
three types of color pigments is present in each of the different cones,blue,
green, or red
Constituting protein portions, or the opsins—called photopsins in the cones
The absorption characteristics of the pigments in the three types of cones
show peak absorbencies at light wavelengths of 445, 535, and 570 nanometers
20. Colour vision
Three types of cones
Sensitive to wavelengths particular to Red, Blue and Green colours
Rest of the colours are perceived as a result of partial degree of stimulation
of more than one types of cones
