The Retina of the Eye: Structure, Layers, and What It Is Responsible For

The retina is the part of the eye where light is converted into a signal that the brain understands. An ophthalmologist often writes in the report "macula," "optic disc," "retinal layers" — and you finally want to understand what is meant. Let's go through the anatomy in plain terms, without formulas.

What the retina is and where it is located

The retina is the inner lining of the eye and the peripheral part of the visual analyzer. It lines the eyeball from the inside: on one side it is adjacent to the vitreous body, on the other — to the choroid. Here lie the photoreceptors, which convert light into nerve impulses.

Light passes through the cornea, pupil, and lens, reaches the retina — the photoreceptors convert it into signals, and along the optic nerve they travel to the brain, where the picture is assembled.

In an adult, the retina, about 22 mm in diameter, covers approximately 72% of the inner surface of the eyeball. Its thickness is uneven: at the edge of the optic disc — up to 0.5 mm, in the fovea — minimal. The visual part extends to the ciliary body; the anterior, blind part contains no photoreceptors.

How the retina is structured: 10 layers

The layered structure is visible only under a microscope. Going deeper into the eyeball are: the pigment layer, the photosensory layer, the external limiting membrane, the outer nuclear layer, the outer plexiform layer, the inner nuclear layer, the inner plexiform layer, the ganglion cell layer, the nerve fiber layer, and the internal limiting membrane.

The retina has three layers of nerve cells and two layers of synapses. Photoreceptors lie farthest from the center, ganglion neurons — deep within: light must pass through all the layers before reaching the rods and cones. Connections are provided by bipolar, horizontal, and amacrine cells, and all layers are penetrated by Müller glial cells.

Rods, cones, and the macula

Each retina has about 6–7 million cones and 110–125 million rods. There are more cones in the center and more rods in the periphery.

About 3 mm from the optic disc lies the macula, and within it — the fovea. This is the area most sensitive to light, responsible for clear central vision, and the fovea contains only cones. The central part is the fovea and the zone within a 6 mm radius around it; beyond that begins the periphery, where the number of rods and cones decreases, up to the ora serrata with no photosensitive elements.

The optic disc, with an area of about 3 mm², has no photoreceptors — this is the blind spot, or Mariotte's spot. Through a depression in its center pass the vessels that supply the retina.

Retinal vessels and blood supply to the eye

Vessels enter the eye through the optic disc and branch along the inner surface of the retina — they are visible during examination of the fundus. Both arterial hypertension and diabetes mellitus damage the capillaries that supply the retina with blood.

The outermost, pigment layer is more closely connected to the choroid than to the rest of the retina: this membrane also participates in nourishing the inner lining of the eye.

Which problems affect the retina

Retinal disorders cause blurred or distorted vision, and some lead to vision loss. Age is a common factor; risk is increased by smoking, obesity, diabetes and hypertension, eye trauma, and a family history of retinal diseases.

The more common ones are age-related macular degeneration (dry and wet), diabetic retinopathy, retinal detachment and tears, retinoblastoma (a rare cancer, more often in young children), macular pucker, macular hole, floaters, and retinitis pigmentosa.

You can notice the following in yourself:

• blurred or distorted vision;
• loss of central or peripheral vision;
• flashes of light and floating spots, "cobwebs";
• difficulty seeing in the dark.

Retinal detachment is an emergency. 103/112 — if vision has dropped sharply, flashes of light have appeared, or suddenly there are many more floating spots and "cobwebs" before the eye.

How the retina is examined and when a doctor is needed

The main thing is an examination with a dilated pupil: drops dilate the pupil, and the doctor sees the retina over its entire area. Additionally, OCT is performed — detailed images of the internal structures of the eye, fluorescein angiography of the retinal vessels, and perimetry, which measures peripheral vision.

Protective and sunglasses, regular vision checks, quitting smoking, and control of diabetes and blood pressure are what reduce the risk. Some retinal diseases are related to age or genetics, and they cannot be prevented.

This material is for reference: it helps to read an ophthalmologist's report but does not replace a doctor's consultation.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer