RETINA

Retina

The retina is the light-sensitive tissue on the inside and back of the eye.

Vision originates in the retina, which contains photoreceptor cells that convert light into electrical impulses.

These impulses are the visual information or “pictures” that travel to the brain via the optic nerve.

Most retinal disorders involve a disruption in the transmission of these impulses.

There are many kinds of retinal disorders, with a wide variety of causes and symptoms.

What are the symptoms of retinal disorders?

Symptoms include:

• a white pupil
• a loss or partial loss of vision
• night blindness
• a shower of black floaters in vision
• sudden, persistent flashing lights
• an intolerance of light

Tests for evaluation of retinal diseases

Apart from the routine tests that most ophthalmologists and retinal specialists perform, like visual acuity testing, intraocular pressure check and slit lamp examination, here is a list of tests that an expert may advise for a detailed retinal evaluation.

• Amsler Grid test
• Indirect Ophthalmoscopy
• Colour Vision Test
• Visual Field Test
• Optical Coherence Tomography
• Fundus Fluorescein Angiogram
• Indo-Cyanine Green Angiography (ICG)
• Ultrasound
• Electroretinogram (ERG)
• Electroculogram (EOG)
• Visual Evoked Response

Common eye conditions that affect the retina include

DIABETIC RETINOPATHY

Diabetes affects the eye in various ways.

• Diabetic retinopathy
• Cataract
• Glaucoma

Cataract requires cataract surgery and implant of an artificial lens (or intraocular lens), while glaucoma refers to increase in pressure of the fluid inside the eye (aqueous) that leads to optic nerve damage and loss of vision. A person with diabetes is nearly twice as likely to get glaucoma as other adults.

Diabetic retinopathy refers to damage to the retina caused by abnormal blood flow related to diabetes mellitus, which can potentially lead to severe loss of vision.

In some people with diabetic retinopathy, blood vessels may swell and leak fluid. In other people, abnormal new blood vessels grow on the surface of the retina. The retina is the light-sensitive tissue at the back of the eye. A healthy retina is necessary for good vision.

Diabetic retinopathy usually affects both eyes.

Remember:

• If you have diabetes get a comprehensive dilated eye exam at least once a year.
• Proliferative retinopathy can develop without symptoms. At this advanced stage, you are at high risk for vision loss.
• Macular edema can develop without symptoms at any of the four stages of diabetic retinopathy. You can develop both proliferative retinopathy and macular edema and still see fine. However, you are at high risk for vision loss..
• Whether or not you have symptoms, early detection and timely treatment can prevent vision loss.

Treatment for Diabetic Retinopathy:

The usual treatment paradigms for the disease are:

1. Laser treatment
2. Anti-VEG-F treatments
3. Retinal Surgery

Macular Degeneration

Age-related macular degeneration (AMD) presents as difficulty in reading small print, or seeing faces, leading to progressive loss of central vision. AMD is the most common cause of vision loss in individuals over 55 years of age.

There are two types of macular degeneration;

·         ‘wet’ type (about 10% of cases) that can lead to severe loss of vision and needs treatment in most cases, and

·         ‘dry’ type seen in about 90% of cases that does not usually progress to significant visual loss.

Treatment:
Dry AMD: No medical or surgical treatment is available at this time. However, vitamin supplements with antioxidants, lutein and zeaxanthin, have been suggested by a National Eye Institute, USA sponsored study.

Wet AMD: Anti-angiogenics or anti-VEGF (anti-Vascular Endothelial Growth Factor) agents have been shown to be effective in causing regression of the abnormal blood vessels and improvement of vision when injected directly into the vitreous cavity of the eye.

The injections have to be repeated monthly or in six weeks.

Agents such as Ranibizumab (Lucentis), Bevacizumab (Avastin), and Pegaptanib (Macugen) are routinely used these days. Only Ranibizumab and Pegaptanib are approved by the FDA for AMD, though Bevacizumab is used off-label.

Photodynamic therapy has also been used to treat wet AMD.

RETINAL DETACHMENT

Retinal detachment is a condition when the retina separates away from its normal position. This can happen at any age, and can lead to sudden or slow loss of vision, depending on the actual cause.

The detachment can occur due to many causes,

including a hole developing in the retina, as sometimes happens in myopia,

pull or traction developing on the retina as can happen in diabetic retinopathy, or

injury to the retina. In most cases, surgery is required to correct this disorder, which should be undertaken sooner to prevent further detachment and potential visual impairment.

RETINITIS PIGMENTOSA (RP) NIGHT BLINDNESS

Retinitis pigmentosa (RP) refers to a group of inherited diseases that lead to slow and progressive retinal degeneration that causes damage to the important cells of the retina, the rods and the cones.

People with RP usually experience night blindness early on, and later may develop progressive and gradual reduction in their vision and field of view.

The diagnosis of retinitis pigmentosa relies upon documentation of progressive loss in photoreceptor cell function by electroretinography (ERG) and visual field testing.

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The mode of inheritance of RP is determined by family history. RP can be inherited in an autosomal dominant, autosomal recessive, or X-linked manner. X-linked RP can be either recessive, affecting primarily only males, or dominant, affecting both males and females, although males are usually more mildly affected.

Genetic counseling depends on an accurate diagnosis, determination of the mode of inheritance in each family, and results of molecular genetic testing.

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Treatment:

·         There is no effective treatment for this condition at this time.

·         Wearing sunglasses to protect the retina from ultraviolet light may help preserve vision.

·         Some studies have suggested that treatment with antioxidants (such as high doses of vitamin A palmitate) may slow the disease in some patients

RETINOPATHY OF PREMATURITY (ROP)

Retinopathy of Prematurity (ROP) affects the retina in premature babies who are born weighing less than about 2.75 pounds (1250 grams) or those born before 31 weeks of pregnancy. This disorder usually affects both eyes at the same time, and is one of the most common causes of visual impairment in childhood.

CANCERS IN RELATION TO THE RETINA

There are two types of cancer in the eye;

Retinoblastoma, which is more common among children,

If the child’s eye looks ‘white’ or appears misaligned, it may mean an abnormality in the eye and this must be investigated. Unfortunately, retinoblastoma can affect both eyes simultaneously

Malignant Melanoma, which tends to strike older age groups.

RETINAL VEIN OCCLUSION

Central retinal vein occlusion (CRVO) is a blockage of the main vein in the retina.
Blockage of the branches of the central vein of the retina is called branch retinal vein occlusion (BRVO).

The blockage causes the walls of the vein to leak blood and excess fluid into the retina which leads to blurring of vision. When the leakage is in the central part of the retina, the vision loss is marked.

CENTRAL SEROUS RETINOPATHY (CSR)

CSR is a condition which causes temporary or permanent impairment of vision. It usually affects men between 20 – 45 years of age and is associated with stress.

A small pool of fluid accumulates under the macula (part of the retina). This typically becomes noticeable when central vision is affected.

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