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.
What is a Macular Hole>?
In certain people, the vitreous is abnormally adherent to the underlying macula, forming very close bonds. During the process of a Posterior Vitreous Detachment, the macula and vitreous do not separate cleanly, instead the vitreous “pulls” on the macula, causing vitreomacular traction; translated as a pulling force on the macular by the vitreous gel. The vitreous may spontaneously release, however, in some cases the tractional forces at the macula causes separation with a tuft of macula being pulled away, causing a macular hole.
This full-thickness defect is usually very small, only about 0.2-0.4mm in diameter, but possesses the ability to cause loss of sharp, central vision that is required for “straight-ahead” activities like reading, driving and recognising faces.
In some rarer case, macular holes may be associated with severe trauma to the eye or retinal detachment. Macular holes do not represent or increase the risk of age-related macular degeneration.
What are the symptoms of a Macular Hole?
Early vitreomacular traction and macular holes may not cause any symptoms. Most holes will progress over weeks to months to form a full-thickness defect and loss of central vision in the affected eye. During this time, symptoms may include:
- Increasing blur of printed words
- Difficulty reading
- Distorted vision (straight lines look wavy)
- Black or grey spot in the central vision of one eye
- Difficulty recognising faces
How are Macular holes detected?
Your Retinal Specialist will enlarge your pupil with dilating drops and use a slit lamp microscope to view the retina and macula in detail. These drops will blur your vision for 2-3 hours and it is recommended that you do not drive on the day of your eye exam.
Optical Coherence Tomography (OCT)
Optical coherence tomography (OCT) allows non-invasive imaging of the macula in cross-section, akin to a high resolution photograph of the back of the eye. This can confirm if vitreomacular traction or a full-thickness macular hole is present. It is also useful in monitoring the response of the macula following surgery.
In fluorescein angiography, a small volume of fluorescein dye (vegetable based) is injected into a vein in the arm via a small cannula, which then travels through the circulatory system into the blood vessles in the eyes. A series of photographs are taken as the dye passes through the blood vessels in the Retina. Fluorescein angiography can be used to rule out other possible retinal conditions that may appear similar to a macular hole.
What treatments are available for Macular Holes?
There are currently no medications, eye drops or laser treatments that can treat a macular hole. Only a surgical procedure performed by a Retinal Specialist, known as a vitrectomy and Macular Hole Repair, can close a macular hole. For best results, surgery should be performed within 6 to 12 months of the macular hole developing. In these cases, 90-95% of macular holes are successfully closed and 85-90% of people will gain a significant improvement in vision. Surgery on long-standing macular holes generally has lower rates of successful closure and vision recovery. Generally, the more lines of vision that are lost pre-operatively are harder to gain back after the post-operative recovery period.
Vitrectomy surgery is performed under local anaesthesia with moderate sedation. Three small instrument ports are inserted through the sclera (white of the eye) at the front of the eye, each approximately half a millimetre wide. Very fine surgical instruments are inserted via these ports and the vitreous is removed under microscopic guidance.
The vitreous and epiretinal membrane that is placing the tractional force on the macula is identified and delicately peeled away, which releases the traction and allows the macula to recover and seal the hole. A careful peripheral retinal examination is performed to ensure there are no retinal tears, holes or areas of weakness.
Following this, a long acting gas bubble is inserted into the back of the eye, which serves to assist in sealing the macular hole during the postoperative period and provides internal support. At the completion of the surgery, the wounds self-seal and sutures are not usually required.
To facilitate correct placement of the gas bubble, you will be required to position facedown for 50 minutes of each waking hour for 5-7 days following surgery. Positioning while asleep may be required in some instances.
What can I expect after Macular Hole surgery?
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.
Vision is generally limited in the first two to six weeks due to the gas bubble which changes the focus of the eye, thus placing all images out of focus. As the bubble is naturally absorbed, your vision will gradually return to normal. Complete vision improvement usually takes 6 to 18 months. Vision will usually be much better but often will not return to normal vision before the macular hole developed. In particular, mild distortion of the central vision may persist, although this is usually not noticeable when using both eyes. Additionally, if you have not yet had cataract surgery, a vitrectomy will accelerate the growth of cataract and earlier surgical removal will be required.
Having a gas bubble in your eye will mean that you cannot fly for 2-8 weeks following surgery. It is important that your retinal specialist confirms that the gas has fully dissipated before you fly. Likewise, the use of anaesthetic agents containing nitrous oxide (laughing gas) should be avoided while gas is present in the eye. You will be given a wristband to wear after surgery to inform all medical practitioners that you have gas in your eye.
It is safe to return to light physical activity after you have completed the required period of positioning. You can take up moderate physical activity after two weeks. Heavy physical exercise and exertion should be delayed for at least 6-8 weeks. You may shower and bathe normally following surgery but take care to avoid getting water into the eye during the initial two weeks after surgery.