The substances filling the back of the eye and keeping retinal and other tissues in place are known as humours. The aqueous humour fills the space around the crystalline lens and iris in the front part of the eye, and the vitreous humour, sometimes called the vitreous body, a relatively thick gelatin-like substance, keeps the back of the eye rounded and supports the retinal tissues, holding them snugly against the rounded inner surface of the globe.
As we age, it is normal for the gel-like vitreous humour to begin to break down somewhat into its components, protein strands and liquid. This is a process known as syneresis, which is considered to be a normal condition that can result in fluid-filled pockets that are mostly liquid but contain small amounts of collagen. When these pockets exist in close proximity to the retinal tissue, they can result in separation of the vitreous often seen in the older population called posterior vitreous detachment (PVD). This is not abnormal and is not dangerous, but a naturally occurring process.
However, if the separation of the vitreous and the retina is not complete, there may be areas of focal attachment or adhesions which can lead to pulling or traction on the tissue, known as vitreomacular adhesion (VMA). Depending on the strength of the adhesion, the pulling on the retinal tissue can lead to traction-related complications, especially apparent in the area of the macula, where humans get their clear, central vision. VMA traction can result in swelling or edema within the retina, damage to the tiny retinal blood vessels, and to the optic nerve where signals are sent to the brain. Macular puckers, macular holes, swelling and separation of retinal layers, can occur, resulting in vision that is distorted or blurred, and even loss of sight in the center of the field of view.
Enter Ocular Coherence Tomography (OCT)
Ocular Coherence Tomography (OCT) is probably the most important advancement in visual examination equipment in recent memory. This sensitive instrument uses non-invasive imaging techniques and sophisticated computer software to provide eyecare practitioners with highly detailed cross-section views of the retina and the optic nerve head. OCT is now being used extensively to diagnose and monitor eye conditions such as glaucoma, age-related macular degeneration, retinopathy of diabetes, and many others. In this instance, it is used to evaluate traction on the retina from collagen strands in the vitreous. OCT is providing the means for much earlier diagnosis and treatment of VMA, particularly in cases where the VMA is causing traction on the retinal tissue.
Thanks to OCT, eyecare practitioners can now view and diagnose much more accurately the conditions where such traction is occurring; VMA that causes symptoms like visual distortion or impairment is known as symptomatic VMA.
Previously, symptomatic VMA was treated by the surgical removal of the vitreous and replacing it with a saline solution; the procedure is known as a pars plana vitrectomy (PPV). Unfortunately, there are serious risks associated with PPV, including retinal detachment and tears, cataract formation, and endophthalmitis, a serious inflammation involving the entire eye.
In 2014, a new pharmaceutical, ocriplasmin, was approved for use in Canada and the US. Ocriplasmin is a recombinant enzyme that targets the protein/collagen strands causing traction on retinal tissue. Given via injection, ocriplasmin provides a non-invasive, non-surgical treatment for symptomatic VMA. This new drug is now available as the trade name drug Jetrea and is being used by ocular surgeons as a safer and more effective treatment than vitrectomy. Ongoing studies confirm that ocriplasmin injection results in quicker resolution of visual distortions, faster recovery time, fewer complications and reduced cost.
Advancements for Now and the Future
Ocriplasmin represents the progress being seen in drug research targeting specific conditions, as OCT scans are providing the means to better diagnose retinal traction associated with vitreomacular adhesions; together these two advancements should be the means of preventing the loss of vision due to symptomatic VMA.
It is important to see an eyecare practitioner as soon as possible if symptoms of distorted vision or flashes of light, particularly if they occur suddenly. Many people experience flashes and floaters, which are not in themselves dangerous, but any significant change in their location or number should be checked.