Retina is the third and inner coat of the eye which is a light-sensitive layer of tissue. The optics of the eye create an image of the visual world on the retina (through the cornea and lens), which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses. These are sent to various visual centres of the brain through the fibres of the optic nerve. Thus a person with a normal eye but a retinal disease will have poor vision.
The common diseases affecting the retina are:
• Retinal detachment
• Retinal vascular diseases e.g. Diabetic retinopathy, Hypertensive Retinopathy, Venous occlusions, Arterial occlusions.
• Macular disorders e.g. ARMD, CSCR, CNVM, macular dystrophies
• Vitreous Haemorrhage
• Retained intraocular foreign body
• Anterior segment complications e.g. Subluxated lens. Dropped Nucleus, Dropped IOL, Endophthalmitis etc.
These can be managed by both medical treatment &surgical treatment depending upon the stage of presentation and type of disease.
- Fundus Fluorescein Angiography
- Optical Coherence Tomography
- B - Scan Ultrasound
Fundus Fluorescein Angiography (FFA) is a diagnostic test to determine the health of retinal blood vessels. In this test we inject a small quantity of water soluble dye, sodium fluorescein is injected intravenously and pictures of the retina in the early, mid and late phase are taken at a rapid sequence with fundus camera. Abnormal blood vessels will show leakage of the dye. The site, severity, and time of leakage determine the disease pattern and guide the course of treatment and follow up.
This is a very safe test but adverse reactions are seen occasionally, the most common being nausea and vomiting, dark colored urine and skin may look yellow for a day or two. Serious side effects e.g. anaphylaxis which can be life threatening though rare have been observed.
Optical Coherence Tomography (OCT) is a non-invasive test and works on the principle of laser interferometry. Retinal slices are cut and viewed at different planes and at different places. Macular thickness pre and post treatment can be quantified e.g. in diabetic macular edema. Intraretinal or subretinal pathology can be detected and followed.
Common Disorders of the Retina
Diabetic retinopathy (DR) is a common vascular retinal disease affecting about 40% of type 1 diabetics and 20% of type 2 diabetics. Duration of the diabetes is the most important risk factor for DR.
All people with diabetes - both type 1 and type 2 - are at risk. That's why everyone with diabetes should get a comprehensive dilated eye exam at least once a year. The longer someone has diabetes, the more likely he or she will get diabetic retinopathy.
Diabetic retinopathy is symptomless in the early stages. By the time symptoms appear it become too late to stop the process of deterioration. The golden rule in diabetics is "Regular, frequent dilated eye examination."
Non proliferative diabetic retinopathy is characterized by leakage of small blood vessels in the retina, which causes reduced vision. Proliferative retinopathy is characterized by the growth of new blood vessels on the surface of the retina, which may lead to vitreous hemorrhage and retina detachment.
- Cataract often occurs at a younger age in diabetics.
- Decrease in vision due to ClinicallySignificant Macular Edema which affects the fine vision.
- Neo vascular Glaucoma can cause damage to the optic nerve and almost impossible to treat and control.
- At times diabetes can also cause weakness of the optic nerve or eye muscle.
- A diabetic patient is also more likely to develop sudden vision loss due to occlusion of the retinal vessels (branch or central retinal vein occlusion), vitreous haemorrhage, retinal detachment, or infections of the cornea and vitreous.
Diabetic retinopathy is detected during a comprehensive eye exam that includes:
- Visual acuity test: This eye chart test measures how well you see at various distances.
- Dilated eye examination: Drops are placed in your eyes to dilate the pupils (Fundoscopy). Retina is examined for any signs of the disease.
- To confirm diagnosis, to know the extent of damage, to plan treatment schedule and to record various changes for future reference we may suggest a FFA and OCT.
- The indications for treatment depend on extent of severity of the disease.
- The various treatment options include Intravitreal VEGF inhibitors, Steroids, Laser Photocoagulation and Surgery.
A retinal detachment is a separation of the neurosensory layer from Retinal Pigment Epithelium. Most retinal detachments are a result of a retinal break either hole or tear.
- Flashing lights and floaters
- Shadow or curtain that affects any part of the vision
- Younger adults (25 to 50 years of age) who are have a high minus number (myopic)
- Associated with peripheral retinal degenerations
- Older people following cataract surgery.
- Blunt trauma, as from a tennis ball or fist.
- Penetrating injury by a sharp object.
- A family history of a detached retina.
- In as many as 5% of patients with a non-traumatic retinal detachment of one eye, a detachment subsequently occurs in the other eye. Accordingly, the second eye of a patient with a retinal detachment must be examined thoroughly and followed closely, both by the patient and the ophthalmologist.
- Diabetes can lead to a type of retinal detachment that is caused by pulling on the retina (traction) alone, without a tear.
Retinal detachment can be prevented by doing prophylactic barrage laser. Barrage laser is indicated in following conditions
- One eyed, Myopic, Aphakic
- History of RD in fellow eye
- Symptomatic peripheral retinal degenerations
A tear or hole of the retina that leads to a peripheral retinal detachment causes the loss of side (peripheral) vision. Almost all of these patients will progress to a full retinal detachment and loss of all vision if the problem is not repaired. Early diagnosis and repair are urgent since visual improvement is much greater when the retina is repaired before the macula or central area is detached.
Age-related macular degeneration (AMD) is a disease that affects the macula by accumulation of metabolic bye products and thus blurs the sharp, central vision for activities such as reading, sewing, and driving.
- The greatest risk factor is old age.
- Smoking - Smoking may increase the risk of AMD
- Obesity - Research studies suggest a link between obesity and the progression of early and intermediate stage AMD to advanced AMD
- Race - Whites are much more likely to lose vision from AMD than African Americans.
- Family history - Those with immediate family members who have AMD are at a higher risk of developing the disease.
- Gender - Women appear to be at greater risk than men.
• Visual acuity test
• Dilated eye exam
• Amsler Grid Test