The retina is a very delicate, photosensitive membrane that lies on the inside of the eyeball.
The role of the retina is to convert the light signal into an electrical impulse that is further transmitted via the optic nerve to the brain. This is possible due to the highly sophisticated and precise structure of the retina, i.e. the various types of cells found in it, the most famous of which are rods and cones.
The retina is divided into peripheral and central zones, enabling different visual functions such as detailed central vision, color perception, vision in dim lighting and peripheral vision.
The thickness of the retina is 0.1-0.25 mm
We distinguish three parts of the retina:
- Visual part ( pars optica )
- Ciliary part ( pars ciliaris retinae )
- Iris part ( pars iridica )
- The border between the visible ( pars optica ) and the blind ( pars coeca ) part of the retina is formed by the jagged line of the ora serrata.
Histologically, the retina is divided into 10 layers, looking from the inside out:
- Internal boundary membrane
- A layer of nerve fibers
- Ganglion cell layer
- Inner mesh layer
- Inner granular layer
- Outer mesh layer
- Outer granular layer
- Outer boundary membrane
- A layer of cones and sticks
- Pigment layer
Optic nerve head (papilla n. optics) it is the place where the retinal nerve fibers coming out of the eyeball (blind spot) gather and form the optic nerve.
The area we call the macula or yellow spot ( macula lutea ) occupies, in a broader sense, the area of the posterior pole, which is also called the central region.
In the center of the macular area is the fovee centralis, which contains only cones, and is the place of sharpest vision.
Light waves with a length of 400 to 700 millimicrons act on the eye’s neuroepithelial cells to cause light sensation. The retina is most sensitive to wavelengths between 510 to 550 millimicrons.
Photoreceptors consist of rods and cones.
- There are about 130 million sticks
- Čunjić has about 6.5 million
Cones are concentrated in the central fovea where there are no rods, but they are also sparsely distributed on the retinal periphery.
The peripheral part of the retina serves to see in the dark and detect movement.
The composition of rods and cones is similar, and the outer boundary membrane divides them into two parts. In the outer part, there are several hundred discs, each of which has a certain amount of visual pigment (rods rhodopsin, cones iodopsin). Such a structure of the discs enables the transformation of light into chemical energy.
Diseases of the retina
Diabetic retinopathy
A very common cause of blindness.
The basic therapy is photocoagulation of the retina using a laser.
Retinal ablation
A disease characterized by detachment of retinal sensors from the retinal pigment epithelium. The cause of this phenomenon is the passage of liquid and diluted vitreous through the retinal rupture into the retinal space. Visual acuity is reduced to a greater or lesser extent. It occurs more often in myopes than in emmetropes or hypermetropes. The longer the retinal detachment lasts, the worse the visual acuity, so retinal detachment should be performed sooner.
Senile macular degeneration
Risk factors are high blood pressure, smoking and increased exposure to sunlight. The clinical sign of the disease is the weakening of vision in one eye, and the patient complains of metamorphopsia and photophobia.
Senile macular degeneration is a progressive and degenerative disease, and is one of the main causes of blindness in developed countries. The prognosis for recovery of visual function is often not good, despite treatment.
Autor:
bc. Livio Svržnjak, optometrist
