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Retina: Structure, Function and Disorders

The retina is the light-sensitive layer at the back of the eye that captures visual signals and transmits them to the brain. It is essential for vision.

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Things worth knowing about "Retina"

The retina is the light-sensitive layer at the back of the eye that captures visual signals and transmits them to the brain. It is essential for vision.

What is the Retina?

The retina is a thin, light-sensitive layer of tissue that lines the inner back wall of the eyeball. It functions similarly to the film in a camera: it captures incoming light, converts it into electrical signals, and transmits these signals via the optic nerve to the brain, where visual perception takes place. Without a healthy and intact retina, normal vision is not possible.

Structure of the Retina

The retina consists of several layers of specialized nerve cells. The most important are the photoreceptors, which are divided into two types:

Rods: Approximately 120 million rod cells are responsible for vision in low light and twilight conditions, as well as detecting movement.
Cones: Approximately 6 million cone cells enable color vision and sharp daytime vision. They are concentrated in the macula (also called the yellow spot), particularly in the fovea centralis, the area of sharpest vision.

Additional retinal layers include bipolar cells and ganglion cells, whose axons form the optic nerve. At the point where the optic nerve exits the eye, there are no photoreceptors, creating the so-called blind spot.

Function of the Retina

Light entering the eye through the cornea, lens, and vitreous humor is focused onto the retina. The photoreceptors respond to different wavelengths of light and convert these optical signals into electrical nerve impulses through a biochemical process called phototransduction. These impulses travel along the optic nerve to the visual cortex in the brain, where the image is processed and interpreted.

Common Retinal Disorders

Retinal Detachment

A retinal detachment occurs when the retina separates from the underlying choroid layer. This is a medical emergency that can lead to permanent blindness if not treated immediately. Warning signs include sudden flashes of light, a sudden increase in floaters (small dark spots or threads), and a dark curtain or shadow spreading across the visual field.

Diabetic Retinopathy

Long-term diabetes mellitus can damage the tiny blood vessels of the retina, leading to diabetic retinopathy -- one of the leading causes of blindness in working-age adults. Regular eye examinations are therefore essential for people with diabetes.

Age-Related Macular Degeneration (AMD)

Age-related macular degeneration is one of the most common eye conditions in people over 50. It affects the macula and leads to progressive loss of central vision. There are two forms: the slower-progressing dry AMD and the faster-progressing wet AMD, which can be treated with medication.

Retinitis Pigmentosa

Retinitis pigmentosa is an inherited condition in which the photoreceptors -- primarily the rods -- gradually degenerate. Affected individuals first notice a decline in night vision and a narrowing of their visual field over time.

Diagnosis of Retinal Conditions

Ophthalmologists use various examination methods to assess the health of the retina:

Ophthalmoscopy (funduscopy): Direct visualization of the retina through the pupil using an ophthalmoscope.
Optical Coherence Tomography (OCT): High-resolution cross-sectional imaging of retinal layers without radiation exposure.
Fluorescein Angiography: Imaging of the retinal blood vessels using an injected dye to detect leakage or blockage.
Visual Field Testing (Perimetry): Assessment of the full extent of the visual field to detect any gaps or defects.

Treatment of Retinal Conditions

Treatment options depend on the specific condition and its severity:

Laser Photocoagulation: Targeted laser treatment to seal leaking blood vessels or retinal tears.
Intravitreal Injections: Injection of anti-VEGF medications directly into the vitreous to treat wet AMD or diabetic retinopathy.
Vitrectomy: Surgical removal of the vitreous humor, commonly performed for severe retinal detachment.
Cryotherapy: Application of freezing temperatures to treat retinal tears and prevent detachment.

Prevention and Eye Health Tips

To maintain retinal health, experts recommend the following measures:

Regular eye examinations, especially from the age of 40 or if you have diabetes or high myopia
Protection from UV radiation by wearing sunglasses with certified UV protection
A balanced diet rich in lutein, zeaxanthin, omega-3 fatty acids, and vitamin C
Avoiding smoking, as tobacco use significantly increases the risk of AMD
Careful management of blood sugar levels in people with diabetes

References

Yanoff, M. & Duker, J. S. - Ophthalmology. 5th edition. Elsevier, Philadelphia, 2019.
Bhavsar, A. R. - Diabetic Retinopathy. In: StatPearls. StatPearls Publishing, Treasure Island (FL), 2023. Available at: https://www.ncbi.nlm.nih.gov/books/NBK560805/
World Health Organization (WHO) - World report on vision. Geneva, 2019. Available at: https://www.who.int/publications/i/item/9789241516570

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