What is Retina?
The retina is that portion of the innermost part of the eye which is light sensitive. The retina is like a camera as it helps in creating the image. The photoreceptor cells, cones and the rods are the ones responsible for receiving the light and this is sent to the brain through the optic nerves by transforming it into image forming signals. Actually the optic nerve can be said to be a central tract which is the connecting factor of the retina and the brain. Another important feature of the retina is that it is the only part which belongs to the central nervous system (CNS) which can be directly imaged.
The retina is made up of many layers, 10 to be precise. The different layers from the innermost to the outer one are listed below:
- Inner Limiting Membrane
- Nerve Fiber
- Ganglion Cell: the one responsible for producing the optic nerve fibers.
- Inner Plexiform Layer
- Inner Nuclear Layer
- Outer Plexiform Layer
- Outer Nuclear Layer
- External Limiting Membrane
- Photoreceptor Layer
- Retinal Pigment Epithelium
The retina is quite a complex portion of the eye. An adult’s retina is said to have a diameter of about 22 mm. the retina constitutes 72% of the entire area of a sphere. The retina is made up of 75-150 million rods and 7 million cones, figures which are even difficult to fathom. An image is created with the functioning of both the cones and the rods. The cones are the ones that react when bright light falls and decides upon high resolution and color vision whereas the rods react to dim light and arbitrate regarding lower resolution vision, night vision and also black and white vision. Cones that are sensitive to light that are green, red and blue in color are absent in certain individuals which causes color blindness problems and various other color vision deficiencies. Since humans have 3 cones as compared to other mammals which have two (they lack the red sensitive cone), the color vision of humans becomes superior. The retina functions in a truly amazing pattern by compressing the image size to fit the scope of the optic nerve.
The retina is also prone to various diseases such as macular degeneration, retinal separation, retinoblastoma and many others. There are various instruments and treatment methods available today so as to diagnose and treat these problems at the earliest. The retina is a crucial part of the eye and for good vision one would need a healthy retina lifelong.