The wall of the eyeball has three main layers – the outer fibrous layer (sclera, cornea), middle vascular and muscular layer (choroid, ciliary body and iris) and the inner neurosensory layer (retina). All three layers adhere to each other and both the outer and inner layers are highly dependent on the rich blood supply of the middle layer for oxygen and nutrients.
The retina is the inner lining of the eyeball which is best known for housing the light-sensitive receptors that are the main functional component of the sense of vision. It is has several layers to allow it to complete its function :
- Inner limiting membrane
- Nerve fiber layer (optic nerve fibers)
- Ganglion cell layer (ganglionic layer)
- Inner plexiform layer
- Inner nuclear layer
- Outer plexiform layer
- Outer nuclear layer
- External limiting membrane
- Layer of rods and cones
- Retinal pigment layer (retinal pigment epithelium ~ RPE)
The inner limiting membrane is in contact with the vitreous humor, the gelatinous substance that fills the posterior segment of the eyeball. The retina has its own blood supply derived from the retinal artery which feeds the inner layers. However, the outer layers of the retina rely on the highly vascular choroid (middle layer of the eye) for its blood supply. Should the retina be separated from the wall of the eye, its inner layers may be able to sustain itself but the outer layers will degenerate since it has an insufficient supply of oxygen and nutrients.
What is a detached retina?
Retinal detachment or a detached retina is the separation of the inner layers of the retina from the retinal pigment layer or the entire retina from the underlying choroid. This separation compromises the blood flow to some of the inner retinal layers and with time this tissue can degenerate. Fortunately, the tissue degeneration does not happen immediately and can even survive for days in this state but nevertheless requires urgent attention to prevent loss of vision.
Types of Retinal Detachment
Different mechanisms gives rise to the three types of retinal detachment :
- Rhegmatogenous detachment
- Traction detachment
- Serous detachment (or exudative detachment)
Rhegmatogenous Retinal Detachment
This is the most common type of retinal detachment. Here vitreous humor leaks into underlying areas through a hole or tear in the retinal layers. The humor then accumulates between the neural layers and retinal pigment layer thereby separating it.
Traction Retinal Detachment
This type of retinal detachment arises when adhesions develop between the retina and vitreous humor. This pulls the outer retinal layers away from the wall of the eye.
Serous Retinal Detachment
Fluid from the surrounding vessels pass into the subretinal space thereby separating the entire retina from the underlying choroid.
Causes of a Detached Retina
The causes may vary depending on the type of retinal detachment.
- Trauma to the eye
- Age-related shrinking of the vitreous humor (posterior vitreous detachment)
- Diabetes mellitus – diabetic retinopathy
- Sickle cell retinopathy
- Choroid tumors – hemangioma (benign) or malignant tumors (primary or metastasis)
Patients who are at risk may include :
- Diabetics especially in cases of poorly controlled and long term diabete mellitus
- Undergone previous cataract surgery
Signs and Symptoms of Retinal Detachment
Symptoms can develop suddenly and progress within days to severe loss of vision. Initially there may be :
- Excessive eye floaters
- Flashing lights
- Blurred vision
As the condition progresses, the symptoms become more prominent :
- Loss of peripheral vision – shadow (‘curtain’/’veil’) or grayness
- Central vision then affected within days
It is important to note that retinal detachment is painless.
Diagnosing Detached Retina
Opthalmic examination by a doctor is necessary to detect retinal detachment. Eye drops will be used to dilate the pupils. Indirect funduscopy will allow the doctor to visualize the retina and identify retinal detachment. However this may not be possible in patients with cataracts or vitreous hemorrhage (bleeding). An ultrasound examination may therefore be required.
Treatment of Retinal Detachment
Drug therapy may only be useful in inflammatory conditions like uveitis that lead to retinal detachment. Systemic corticosteroids may be prescribed. Corticosteroids may also be delivered locally by the use of surgical implants.
Procedures such as laser surgery (photocoagulation), heat (diathermy) and freezing (cryotherapy) may heal retinal tears prior to detachment. These procedures are aimed more at prevention rather than treatment of retinal detachment.
Once retinal detachment occurs then the following procedures will be considered :
- Scleral buckling. Indenting the retina by pushing from the outside (sclera) over the affected area.
- Pneumatic retinopexy. Gas or air is injected into the vitreous humor which then creates pressure within the posterior segment (vitreous cavity) and pushes the retina back into place.
- Vitrectomy. Draining the vitreous humor from the posterior segment of the eye and then injecting in gas or fluid into the vitreous cavity.