Retina

Anatomy of Retina

• It is the innermost tunic of eyeball. It is a thin, delicate & transparent membrane.
• It is the most highly developed tissue of eye.
• It appears purplish red.
• Retina divided in to three distinct regions (1) optic disc (2) macula lutea – (3) rest of the peripheral retina

OPTIC DISC : 

• Pale, pink, well defined circular area of about 1.5 mm diameter,which continue as a optic nerve which is connected to the brain.

MACULA LUTEA :

• It is a yellow spot,which is comparatively dark area of 5.5 mm diameter.
• It corresponds to approximately 15 degree of visual field
• A healthy macula is crucial for tasks involving fine vision such as reading, recognizing faces and distinguishing things,identifying different colours.
• Eyeball acts like a camera with a lens in front and a film (retina) at the back. The retina converts the ocular image into a signal that is sent to the brain.
• In front of the retina is the vitreous cavity, which is filled with a gel-like substance, called the vitreous.
• Diseases of the retina, the vitreous, and the optic nerve can cause serious vision problems. Fortunately, most of them can now be managed satisfactorily with modern methods of diagnosis and treatment.

Symptoms and signs of retinal diseases :

Usually the symptoms of retinal diseases are painless, and some may be slight and difficult to notice. When the disease is present in only one eye, the healthy eye will compensate for the other; many people live with a disease for years without knowing.

1. FLOATERS: with age, normally transparent vitreous gel liquefies & breaks up, leading to the presence of little particles & fibrous strands floating in the vitreous cavity. This debris casts shadow onto the retina. Patient complaining of seeing black dots ,rings, strands, spider like images that are more noticeable against a bright background & move even when the eye is stationary. Floaters indicate some form of vitreous degeneration & liquification & are usually age related and also common at younger age in myopic patients. However shower of dots or a sudden increase in their number could indicate formation of retinal tear, especially if associated with flashes of light.
2. PHOTOPSIA: A sensation of flashing lights or flickering lights in one or both eyes.usually age related but could be an indicator of a developing retinal tear or early retinal detachment.
3. Blurred vision or vision loss
4. A dark or empty spot in the center of vision
5. A shadow over a portion of the visual field
6. Poor night vision
7. Difficulty adjusting from bright to dim light
8. Distortion of vision
9. Micropsia : object looking small
10. Macropsia :object looking large

Diabetic Disease of the Retina

Diabetes is the second leading cause of blindness in the world.

Diabetes mellitus is a common disease & occurs in 2 forms :

• Type 1 – Insulin dependent diabetes mellitus (IDDM)
• Type 2 – Non insulin dependent diabetes mellitus (NIDDM)

Almost all patients with type 1 diabetes develop a retinopathy in about 15 years. In those with type 2 diabetes, the risk of diabetic retinopathy increases with the duration of diabetes , accompanying hypertension & smoking. Diabetes have a 20-25 times greater risk of blindness as compared to the normal population. As therapy of the retinopathy will at best stabilize vision or decrease the rate of visual loss, it is important to screen all diabetes annually by examining the retina after dilating pupil so as to institute therapy as early as possible.

WHAT IS DIABETIC RETINOPATHY?

Most persons suffering from diabetes develop changes in the retina over a period of time. This is caused by damage to the small blood vessels (or capillaries) in the retina. Swelling (edema) in the central part of the retina (macular edema) can cause blurring of fine vision. Fragile new blood vessel sprouts may break and bleed into the interior of the eye, causing blurring of the vision. In the early stages of the disease the vision remains good, therefore, the disease may escape notice. That is why it is essential to have regular retinal examinations if you know that you have diabetes.

TYPES OF DIABETIC RETINOPATHY

1. Non proliferative diabetic retinopathy(NPDR) -mild, moderate,severe,very severe
2. Proliferative diabetic retinopathy(PDR)
3. Diabetic maculopathy

Retinal changes are the major problem, but at times diabetes can also cause a rise in eye pressure (glaucoma), clouding of the lens (cataract), and weakness of the optic nerve or eye muscle. Damage to the small vessels of the optic nerve can affect vision, and weakness of the eye muscles may cause double vision. A diabetic is also more likely to develop sudden vision loss due to occlusion of the retinal vessels (branch or central retinal vein occlusion), bleeding in the vitreous cavity, detachment of the retina, or infections of the cornea and vitreous.

Screening schedule

• Every year, till there is no diabetic retinopathy or there is mild NPDR
• Every 6 months, in moderate NPDR
• Every 3 months, in severe NPDR
• Every 2 months, in PDR

Age Related Macular Degeneration (AMD)

With aging( > 50 yrs of age) some people may develop changes in the macula, the portion of the retina responsible for our central reading vision. TWO TYPES:

1. DRY AMD: responsible for 90% vision loss, mild to moderate vision loss,most common type
2. WET AMD: responsible for 10% vision loss which can be severe. In this type bleeding occurs over macula from abnormally developed blood vessels.

SYMPTOMS :

• GRADUAL DIMNESS OF VISION IN DRY TYPE
• SUDDEN PAINLESS LOSS OF VISION IN WET TYPE
• OTHER COMPLAINTS LIKE DISTORTED VISION,SEEING STRAIGHT LINES SUCH AS THE SIDE OF A DOORWAY APPEAR WAVY,BENT OR FUZZY, SHADOWED AREAS IN CENTRE OF VISION, UNABLE TO RECOGNIZE FACES, UNABLE TO READ PAPERS

ASSOCIATED FACTORS : smoking,blood pressure,high myopia,deficiency of some Vitamins in food

DIAGNOSIS : BY AMSLER GRID CHART, FUNDUS ANGIOGRAPHY, OPTICAL COHERENCE TOMOGRAPHY

TREATMENT :

1. LATEST TREATMENT: (ANTI VEGF THERAPY) AVASTIN OR LUCENTIS type injections in the eye helps to prevent further vision loss and can improve vision
2. PHOTODYNAMIC THERAPY(PDT) : IN this treatment, visudyne drug is injected in to patient vein,which will be excited by light & then application of lasers over retina,helps preventing damage to normal layers of retina by lasers & also blocking abnormal vessels.

Retinal Detachmen

Treatment:

1. Scleral buckling surgery
   In this operation ,placement of a permanent silicon patch (buckle) on the wall of your eyeball. The external stitches will melt away and do not have to be removed. Usually the eye responds to one operation; occasionally, additional surgery may be required
2. Vitrectomy with injection of air, gas or silicone oil inside eye
   (ADVANCED HIGH END ACCURUS VITRECTOMY MACHINE (ALCON) FOR COMPLICATED RETINAL SURGERY)
3. cryotherapy
   ‘Cryo’ means extremely cold or freezing. This operation employs a delicate instrument that freezes small spots, which are transformed into pinpoint scars that strengthen the retina. The temperature required for cryosurgery is approximately minus 70 degrees centigrade.

Investigations for Retinal Dieseases

Fluorescein angiography is a test that use special cameras to photograph the structures in the back of the eye. These test is very useful for locating the damage to the blood vessels that nourish the retina and, in turn, checking on the health of the retina itself. In this test, a colored dye is injected into a vein in the arm of the patient. The dye travels through the circulatory system and reaches the vessels in the retina and those of a deeper tissue layer called the choroids.

PROCEDURE

You will have to give your consent before the procedure. You should have a light meal before undergoing the procedure and be accompanied by a family member or friend.
Eye drops will be put in your eyes to enlarge the pupils — this takes approximately 30 minutes. You will then be asked to sit still in front of the camera while a series of colour photographs of your eyes are taken. You will be given an injection in your arm, and more photographs will be taken.
The test takes approximately 15-30 minutes.

SIDE EFFECTS

Safe Procedure.
Still some side effects like, mild nausea, vomiting discoloration of skin & urine.

The thickness of the retina can be accurately measured by Optical Coherence Tomography (OCT). This recently developed instrument allows for topographical analysis of irregularities in contour of the retinal surface as well as painless measurement of the retinal thickness down to a small fraction of a millimeter. This technique works by reflecting light off the retina which is then captured by a computer which measures the differences in the density of the reflected light.

The following precautions should be observed for three weeks:

• Do not lift anything that weighs more than five kilograms.
• Do not bend over so that your head is below your waist.
• Avoid sleeping on the operated side, unless you are instructed to do so.
• Avoid sexual intercourse.
• Avoid alcoholic beverages.
• Do not rub the operated eye.
• Avoid vigorous activity.
• No automobile trips except to visit the doctor.
• You may bathe carefully from below your neck and shave, but do not get the eyeball wet for at least two weeks. You may carefully clean the orehead and cheek with a wet cloth.
• You may watch television sparingly.
• You may gently rub the eyelids with cotton or a clean tissue moistened with warm water. Do not bathe the eyeball.
• Always wear either protective glasses or an ‘eye shield’ to avoid accidental injury.
• Sleep in a position as advised by your doctor.