To understand what exactly happens in retinal detachment, it is necessary to know its anatomy. Retina is the photosensitive layer of the eye on which the image of objects seen is formed. It is 0.5 mm in thickness and is found at the back of the eye, in front of choroid. The latter is a layer rich in blood supply and vessels arising from it supply blood to 60 to 80% of the retina. “Choroidal blood vessels" mainly provide nourishment to the outer retina. The “central retinal artery" enters the retina along with the optic nerve and supplies blood to the inner retinal tissue. The space in front of the retina and behind the lens is filled with “vitreous humor", a clear gel.
The light enters the eye through the cornea and is focused onto the retina with the help of the lens. Once the light falls on the retina, it stimulates the photo receptor cells present in it. There are two types of photo receptor cells found in the human eye:
The cones are basically concentrated in a small region in the center of the retina called as the “macula." They help in perceiving the fine details of the objects that are seen. The rods are mainly located in the peripheral parts of the retina and provide peripheral vision. They help to see in dim light. Upon stimulation by light, these rods and cones generate an electrical impulse which is transmitted to the brain through the afferent fibers present in the optic nerve. Upon reaching the brain, this electrical impulse is processed in the optic region of the brain and helps in understanding and identifying the things that are seen.
Retinal detachment is the condition in which the retina separates from the underlying retinal pigment epithelium (RPE) or the choroid. The condition was first identified by de Saint-Yves in early 1700s but its clinical diagnosis only became possible after the invention of the Ophthalmoscope by Helmholtz in 1851.
Retinal detachment is one of the most serious emergencies encountered in the field of ophthalmology, coming next only to central retinal artery occlusion and chemical burns.
Mechanism of Retinal Detachment
The vitreous humor leaks into the space between the retina and the choroid following a retinal detachment. At times, the vitreous humor may shrink resulting in traction on the retina. This leads to the tearing away of the retina from the choroid. A retinal tear is most common in the peripheral region of the eye. The hole created by the tearing off of the retina leads to the seepage of vitreous behind the retina. This paves way for further separation of the retina from its base giving rise to a “total retinal detachment."
Types of Retinal Detachment
Retinal detachment has been classified into three major types :
Rhegmatogenous retinal detachment: Rhegma means a rent or a break. In rhegmatogenous retinal detachment, the vitreous accumulates in between the retina and the retinal pigment epithelium (RPE). The blood supply of retina is compromised to a high degree because of this. Rhegmatogenous retinal detachment is the most common type of retinal detachment encountered.
Tractional retinal detachment: In this type of retinal detachment, either there is shrinking of vitreous or some scar tissue, or there may be adhesions between the retina and the vitreous because of certain conditions like proliferative diabetic retinopathy, sickle cell disease, advanced retinopathy of pre-maturity and penetrating trauma. This causes the vitreous to pull the retina from the RPE. Tractional retinal detachment is more common in the elderly and about 70% of the patients affected by this condition are above the age of 70 years.
Exudative retinal detachment: Exudative or serous retinal detachment is seen when there is accumulation of fluid behind the retina and in front of the RPE as a result of some inflammatory condition of the retina or because of some tumor. It is also seen in conditions like hypertension, central retinal venous occlusion, vasculitis, or papilledema. There is no break in the continuity of the retina in this type of retinal detachment.
Prevalence of retinal detachment
Retinal detachment is commonest in two age groups:
Between the age of 25-40 years as a result of degenerative myopia.
Beyond the age of 60 years when it occurs following a cataract surgery.
Male patients with myopia of more than 6 diopters are at an increase risk of developing retinal detachment. Similarly, patients undergoing cataract surgery without the implant of lens are more prone to develop this condition. In case there is loss of vitreous humor during cataract surgery, then the chances of suffering from retinal detachment are considerably increased.
Risk factors for Retinal Detachment
Some conditions that increase the chances of developing retinal detachment include:
Myopia of more than 6 diopters.
Following a cataract surgery.
Direct trauma to the eyes.
Indulging in sports like boxing and bungee jumping.
Diseases like uveitis, which cause an inflammation of the eyes.
Abnormal growth in the eye.
Lattice degeneration of the eye.
Systemic illnesses like diabetes, sickle cell disease, etc.
A positive family history of the condition.
Certain eye medicines like pilocarpine.
Retinal detachment in the other eye.
About 15% people who have suffered from retinal detachment in one eye meet a similar fate in the other eye. Patients undergoing bilateral cataract surgery increase their chances of developing bilateral retinal detachment by 25 to 30%.
Belonging to Jewish ethnicity increases the chance of developing retinal detachment, while black ethnicity reduces the chances of the same.
Though retinal detachment usually affects people belonging to the age bracket of 40 to 70 years, traumatic detachment of retina is more common in young children and teenagers because of injuries sustained during sports activities.
Signs and Symptoms of Retinal Detachment
Often, retinal detachment goes unnoticed at the onset as it is a painless condition. The earliest symptom of the condition is sensation of a flashing light in front of the eye, called as photopsia, accompanied with specks in the field of vision which seem to float in front of the eyes. Later on, the patient may complain of a loss in peripheral vision which may gradually spread to involve the whole eye. Different individuals complain of a different manner of vision loss. While some may complain of a cloudy or irregular vision loss, others may complain of a film in front of the eyes. In certain patients, the loss of vision is sudden, like a curtain falling in front of the eyes. This is particularly common in traumatic retinal detachment. Some patients may complain of a wavy appearance of objects, a condition called as metamorphopsia.
Floaters often help in differentiating the region of retinal detachment. Appearance of a large floater suddenly in front of the visual axis denotes a posterior vitreous detachment. When the vitreous detaches from its annular ring surrounding the optic nerve, a circular floater is observed.
Visual field defects can help in finding the specific location of the retinal detachment. Superior field defects indicate an inferior retinal detachment and are less noticed by the patients. Inferior field defects are more readily noticed by the patients. Large, black visual field defects are seen in case of bullous detachments whereas flat detachments produce grey areas in the visual field.
Diagnosis of Retinal Detachment
A thorough medical history of the patient is imperative for establishing a diagnosis of retinal detachment. This should include the following points:
Inquire about any history of trauma especially to the eyes or head just immediately or several months before the onset of symptoms.
Inquire about systemic illnesses like diabetes, sickle cell anemia, leukemia, angiomatosis of the central nervous system, eclampsia, pre-maturity, etc,
Inquire about any tumors of breast, melanoma, etc.
Inquire about surgeries like cataract extraction, removal of foreign bodies, any operation involving the retina, etc.
Inquire about previous conditions of the eye like uveitis, glaucoma, ambyopia, vitreous hemorrhages, retinopathy, etc.
Patient should be subjected to a complete examination of the eye. His visual acuity and papillary reaction to light should be checked. Visual field mapping should be done. The intraocular pressure should be measured and a slit lamp examination of the eye should be done. A thorough fundus examination using both direct and indirect fundoscopy should be done. An indirect fundoscopy is the most useful method of determining a retinal detachment. Direct fundoscopy may be useful in detecting vitreous hemorrhage and large detachment of the posterior pole but it cannot detect retinal tears elsewhere as it provides a limited view of the periphery of the retina.
Appearance of a Detached Retina
A detached retina appears undulating and dark grey in color because of the blood vessels which lie in its folds. The retinal surface may have the appearance of an orange peel with a line of demarcation denoting the extent of detachment. The retina is swollen and is clearly visible with a 3- mirror contact lens examination.
Treatment for a Detached Retina
The treatment of a retinal detachment depends upon its type, size and location. A small hole in the retina is generally fixed using cryotherapy or laser therapy. These are done as out-patient procedures and are meant to stop the tear from becoming a total retinal detachment. In these procedures, the edges of the torn retina are fixed to the adjoining retinal tissue by means of freezing or laser treatment.
In case of a complete retinal detachment, there are three main types of procedures that are employed. They are:
Scleral buckling: During this procedure, the tear in the retina is first localized using indirect ophthalmoscopy. The tear is plugged in such a manner that the scar tissue thus formed, prevents the vitreous from accumulating behind the retina. This is achieved by means of freezing, use of electric current or laser. Once the scar tissue is created, a sclera buckle is introduced onto the sclera. A sclera buckle is made up of plastic, sponge or silica and works by applying a continuous pressure on the eye. This pressure helps in keeping the hole in the retinal tissue approximated to the retinal pigment epithelium and prevents the retinal tear from progressing into a complete retinal tear.
Pneumatic retinopexy: It is done as an OPD procedure to treat simple retinal detachments. An inflatable gas is introduced into the vitreous cavity during the procedure. The head is placed in a particular position during the procedure. The gas expands and in the process, approximates the retina to the RPE. Once the retinal tear is indented onto the RPE, it is affixed with the help of freezing, laser or by using electric current. The gas gets spontaneously absorbed into the vitreous within two to six weeks. Incase, the procedure fails to seal the retinal tear, sclera buckling is the next option of choice.
Vitrectomy: In this technique, multiple holes are cut into the sclera to approach the vitreous cavity. Then an inflatable gas is injected into the vitreous space after removing the vitreous humor. The torn retina is relocated. Scleral buckling is usually done as an adjuvant procedure. The gas is spontaneously absorbed and replaced by fluids produced by the eye itself. As it is a complicated procedure, vitrectomy is reserved for large or complex retinal detachments which are caused as a result of the growth of aberrant blood vessels in the vitreous or on the retina because of diabetic retinopathy. Vitrectomy is also reserved for retinal detachments resulting from major ophthalmic infections, hemorrhages in the vitreous cavity and crusts on the retina. Big retinal detachments caused by pulling of scar tissue are also treated by means of vitrectomy. Tractional or exudative retinal detachments are treated through this procedure.
Recent studies have indicated that sclera buckling is the most preferred way of treating retinal detachment and there are fewer chances of recurrence following the procedure.
Medical treatment is generally employed to treat retinal detachments resulting due to inflammatory conditions.
Prognosis of Retinal Detachment
Almost 80% of cases of retinal detachment respond favorably to surgery. !5% of cases may suffer from another retinal tear and require a correction surgery. However, if the treatment is not initiated fast and the retinal detachment involves the macula; permanent blindness may result within 6 months.
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