How do we describe the anatomy of the eye?
The eye is roughly globe shaped and is a complex structure with multiple components that work in unison to form an image on the retina that is perceived as sight by the brain.
The eye can be thought of as analagous to a camera:
- The cornea, which is the transparent covering on the front of the eye, acts much like a lens cover and a focussing element by bending entering light rays through the central ‘black hole’, the pupil, which combined with the coloured iris, the shutter, acts like the aperture of a camera.
- The lens is the next component in line and acts like the lens in a camera by its ability to focus light onto the retina, which acts very much like the film of the camera.
- The retina contains many light sensitive nerve cells called photoreceptors which transmit the light rays into electrical impulses which are delivered to the brain via the optic nerve where an image is perceived.
Similarly to a camera, if the film is of poor quality or malfunctioning, no matter how effective the rest of the components are, the final picture will be poor.
The macula is a small area (5mm) located in the very central part of the retina. There is a greater concentration of photoreceptors at the macula than the rest of the retina, which subsequently provides us with sharp central vision as well as recognition of colours. The macula can be thought of as analagous to the CBD of the retina.
The eyeball cavity itself is filled with a gel-like substance with a similar consistency as uncooked egg white, as is known as the vitreous. The vitreous is normally adherent (in close contact) to the surface of the retina. Around the age of 50-60, the vitreous contracts and separates from the retina. This physiological phenomenon is known as a posterior vitreous detachment (PVD). For more information on PVD, please refer to the section about Floaters, Posterior Vitreous Detachment & Retinal Tears.
The Retina: What is it?
The retina is the light-sensitive layer of tissue that lines the inside of the eye and is responsible for receiving visual stimuli from the environment and processing this information via the optic nerve to the brain. The central 5-10% of the retina, the macula, is responsible for clear central vision. The peripheral retina, as its name suggests, is responsible for peripheral vision. Like all tissues in the human body, it is supplied with nutrients and oxygen via arteries and is drained of waste products by veins. Beneath the retina is a supportive layer of cells called the Retinal Pigment Epithelium, the pigmented cell layer that nourishes the retina, with a further vascular layer beneath this called the choroid, a tissue layer that contains many of these vitally important blood vessels and other structures.
How do Retinal Detachments develop?
Retinal Detachment can occur A retinal tear or hole is potentially the first stage in the development of a retinal detachment. If a full-thickness retinal tear form and isn’t treated, fluid in the vitreous can migrate through the defect and accumulate under the retina. This causes the retina to progressively lift away, or detach, from its normal position.
What is a Retinal Detachment?
As discussed earlier, the retina is a multi-layered light sensitive tissue covering the inside of the eye and sends visual information to the brain. Retinal Detachment refers to the separation of the inner layers of the retina from the underlying Retinal Pigment Epithelium (RPE). A Retinal Detachment is considered to be a medical emergency and prompt referral and treatment should be sought.
There are three different types of retinal detachment:
- Rhegmatogenous Retinal Detachment refers to a retinal tear or break, which allows fluid to effectively dissect the retina away from the underlying nourishing RPE cell layer. This is the most common form Retinal Detachment.
- Traction Retinal Detachment refers to adhesions/scarring between the vitreous gel and the retina, or fibrovascular proliferation causing a surface contraction on the retina. These forces separate the retina from its underlying layers.
- Exudative Retinal Detachment refers to leakage of fluid underneath the retina not due to retinal tears or breaks, but rather due to Retinal Diseases.
What are the symptoms of a Retinal Detachment?
Similarly to a retinal tear, patients may experience new onset floaters, blurred or decreased vision and peripheral bright flashing lights or sparks.
- As the retina detaches – a shadow or curtain may develop in the vision that this area of retina would normally process
- Some people may experience complete and sudden loss of vision.
- The effect on eyesight depends on the location and severity of the detachment. For example, if the retina detaches involving the macula, central vision may be lost.
Who is at risk of developing a Retinal Detachment?
Retinal detachments are most commonly associated with posterior vitreous detachments, however, they can also occur secondary to trauma or other ocular conditions (eg inflammatory or infective ocular disease) and surgery which cause traction on the retina.
The risk of retinal detachment in the general population is low – about 15 per 100,000. It can occur at any age, but is more common over the age of 40 and affecting males greater than females.
A retinal detachment is also more likely to occur in people who:
- Are extremely nearsighted (myopia)
- Have had a retinal detachment in the fellow eye
- Have a family history of retinal detachment
- Have had prior eye surgery, such as cataract surgery
- Have other eye diseases or disorders
- Have had an eye injury
How is a Retinal Detachment detected?
The suspicion of Retinal Detachment is elicited through a careful clinical history and a dilated examination of your eyes. During your appointment with your Retinal Specialist, your pupils will be dilated with eye drops to enlarge the pupil and a specialised lens and microscope will be used to examine the Retina. This process identifies the presence of any retinal holes, tears or detachments.
Ultra wide-field imaging is now available to image retinal pathology in high-resolution detail. This is also useful for monitoring the retina after the detachment has been repaired.
How are Retinal Detachments repaired?
Surgery is the only treatment for retinal detachment. Retinal detachments can be successfully repaired in 98% of cases. A published internal retrospective audit of Dr Bourke's clinical cases over a 2 year period revealed a re-detachment rate of less than 5%, comparing favourable with a 2013 United Kingdom National Audit of Retinal Detachment* where 13.1% of patients required further surgery.
The goals of surgery are:
- Identify the cause(s) of the Detachment
- Re-attach the retina
- Reverse or prevent further vision loss
The prognosis for vision following surgery depends on whether the central vision has been affected by the retinal detachment. If the macula has already detached (macula-off retinal detachment), the ability to read and see fine detail will already be significantly affected and may not recover fully even following successful reattachment of the retina. Only 60-70% of patients restore good central vision in these cases, as compared to 90-95% of patients with macula-on retinal detachments.
The status of the macula in a retinal detachment will also determine how urgently surgery is required. If the macula is still attached, surgery will be performed on a semi-urgent basis to protect the central vision. If the macula has detached, surgery may be performed within 10 days of the loss of central vision without having a significant effect on the final outcome.
The two most common methods of repairing a retinal detachment are vitrectomy surgery and scleral buckling. Both of these are day surgery procedures. The cause, location and type of detachment will usually determine which surgical procedure will work best. Co-existing eye conditions may also influence the type of surgery chosen. The success of each procedure in reattaching the retina and restoring good vision will vary case to case.
What happens during and after Vitrectomy surgery?
Vitrectomy surgery is performed under local anaesthesia and copious sedation. Three small instrument ports are inserted through the white of the eye (the sclera) at the front of the eye. Very fine surgical instruments are inserted via these ports and the vitreous gel is removed under microscopic guidance.
The fluid under the retina (subretinal fluid) is also drained, and the retinal tear(s) are sealed with either laser (endolaser) or freezing (cryotherapy).
The retina is always 100% attached at the conclusion of vitrectomy surgery.
At the conclusion of the operation, depending on the location, severity and amount of the detachment and tears, the eye cavity will be filled with either a long acting gas or silicon oil, which act to seal the tears and support the retina as it heals (laser takes a few weeks to become fully effective). Depending on the location of the tear, you may need to position your head for a few days after surgery to maximise the effect of the gas.
- The gas bubble can last anywhere from 1 to 8 weeks, depending on the type of gas used and its concentration, and you can not fly during this time. Vision through a gas bubble is very poor but it will gradually improve as the gas is reabsorbed by the eye.
- In some cases, silicon oil is used instead of a gas bubble. Silicone oil is much denser than gas and will stabilise the retina for a longer period of time. Silicone oil is not reabsorbed by thebody and a second surgery will be required at some point toremove the oil. Although there is some vision through the silicone oil, it will be blurry, and most patients become long-sighted while oil is in the eye. Silicone oil has many desirable properties such as the ability to fly and provides a long acting internal support of the retina with a simple elective procedure to remove the silicone oil approximately 4-6 weeks after insertion if the post-operative period is uncomplicated.
There is typically no pain following vitrectomy surgery, although you may experience temporary mild-to-moderate redness and grittiness, and swelling and drooping of the eyelid.
Vitrectomy surgery is highly successful, with an 85-95% single surgery reattachment rate. Approximately 5-15% of patients will develop a recurrent retinal detachment after surgery. The most common reason for this is growth of scar tissue across the surface of the retina (proliferative vitreoretinopathy) which causes new retinal tears to form. Recurrent detachments will require further surgery. It is not possible to prevent this scar tissue from growing.
Vision recovery occurs very slowly. If the macula was attached at presentation, good vision will usually return in 4 to 6 weeks, after the gas has fully reabsorbed. However, if the central vision was affected at the time of detachment then it can take anywhere from 3 to 12 months for full vision recovery, and the final vision may still not be as clear as it was prior to the retinal detachment.
In patients who have not had cataract surgery, cataract progression is more rapid following vitrectomy surgery and cataract surgery is usually required within 6 to 12 months. The retinal detachment itself can also predispose certain people to the formation of an epiretinal membrane across the surface of the macula. If the membrane becomes visually significant, it may need to be surgically removed.
In some cases, vitrectomy surgery is combined with scleral buckling, where a silicone band is surgically sutured (stitched) around the exterior of the eye. Scleral Buckling aims to improve success rates in certain types of retinal detachment.
What happens during and after Scleral Buckling?
Scleral buckling surgery is performed under general anaesthesia either in isolation or in combination with a vitrectomy. The retinal tears are usually treated with laser or cryotherapy and the subretinal fluid is drained. A silicone strip (the scleral buckle) is then sewn to the external wall of the eye (sclera) and wrapped around the eyeball like a belt. The buckle will ‘push in’ the eye at the site of tears, and support the retina for 360 degrees.
In order to place the scleral buckle, significant manipulation of the eye’s external tissues and muscles must be performed. Therefore, the eye is often red and swollen following surgery and it can take up to six weeks for the eye to fully recover. The eyeball will look completely normal once it has healed – the scleral buckle is hidden under the outer lining of the eye (conjunctiva) and is almost never visible afterwards.
The scleral buckle is generally left around the eye permanently. In rare cases, the buckle must be removed if there is associated infection or if it works its way through the surface tissues (a process known as extrusion).
Most patients who undergo scleral buckling also experience increased short-sightedness, and there may be a discrepancy in the size of objects between the two eyes. This is correctable to some extent with spectacles or contact lenses. In some cases, the buckle may cause a droop in the eyelid or limit full movement of the eyeball, causing double vision.
Vision recovery after scleral buckling occurs slowly. The vision in the eye is generally poor until an optometrist updates spectacles to the required prescription. This will usually be a minimum of 6-8 weeks after surgery, once the eye has fully healed. Additionally, if the central vision was affected at the time of detachment, it can take anywhere from 3 to 12 months for full vision recovery, and the final vision may still not be as clear as it was prior to the retinal detachment.