For Life recently interviewed Dr Gemmy Cheung from Singapore National Eye Centre on wet age-related macular degeneration (wAMD) and the difference between wet AMD and other conditions such as glaucoma and cataracts.
Q: What is wet AMD?
Age-related macular degeneration (AMD) is one of the leading causes of severe vision loss in older adults in the developed world, if left untreated. Macular degeneration is diagnosed as either dry (non-exudative) or wet (exudative or neovascular) age-related macular degeneration. It occurs when the structures in the back of the eye produce excess VEGF, a naturally-occurring protein which triggers the formation of new blood vessels. This excess VEGF causes the growth of abnormal new blood vessels under the macula – the part of the eye responsible for central vision – which can leak fluid into the eye and damage central vision, causing vision loss. Although we refer to dry and wet AMD (wAMD) as subtypes, wAMD is actually just a progression of the disease, a more severe form of AMD. About 10% of AMD patients go on to develop wAMD. Although it can take many years for a patient to progress from dry AMD to wAMD, once it becomes wAMD the disease progresses much more quickly and can lead to complete and irreversible vision loss in as little as three months.
Q: How is wAMD different from glaucoma and cataract?
The difference between these conditions are characterised by the symptoms and the parts of the eye they affect.
Glaucoma is generally caused by too much fluid pressure in the eye. The function of the fluid in the eye is to nourish and cleanse the inside of the eye and it does so by flowing in and out of the eye. When too much fluid is being produced or the fluid is obstructed from flowing out freely, the intraocular pressure increases and damages the optic nerve, which causes a gradual loss in peripheral vision. Advanced glaucoma patients tend to develop tunnel vision, where their peripheral field of vision decreases. Glaucoma may eventually cause blindness.
A cataract is a cloudiness that occurs in the lens inside of the eye. The lens of the eye is made up mostly of water and protein which are constructed in a way that lets light through. When the protein clumps, the light is blocked and the lens appears cloudy. All of us develop cataracts as we get older. A cataract patient may find that colours appear to fade, develop poor night vision, or see halos which people with normal sight would not perceive.
Macular degeneration affects a small area of the retina which is found right at the back of the eye, known as the macula. The retina to the eye is like the film to the camera. This is where the picture needs to be taken before it gets transmitted to the brain, so it’s a very important structure. The macula is the central area of the retina that allows us to perceive the fine detail of whatever we are looking at directly, like when we are reading or driving. Macular degeneration occurs when the macula is damaged. The wet type of macular degeneration is where abnormal blood vessels develop under the macula and leak fluid.
In age-related macular degeneration, the symptoms are subtler; it tends to start right in the middle of the field of vision. For example, at the early stage of the disease, where one eye is unaffected and the other eye is affected, although the patient may perceive the whole overall picture, he/she may just perceive a little bit of blurring such that when he/she looks at the person across him/her, the central features of the face of the other person may appear a little distorted. If you are developing any distortion of the central vision, central blurring or central vision loss, don’t wait until the whole picture is blurred or distorted. Get it checked out. Also vision loss is usually reversible in a cataract, but that’s not usually the case in AMD.
Q: How is it diagnosed?
Swelling in the retina can be picked up with an eye scan. Suspected cases are then confirmed with an angiogram.
Q: How can wAMD be treated?
It is challenging to treat wAMD as the structure affected is right at the back of the eye where eye drops cannot reach.
Once the angiogram confirms that the patient has wAMD, we’ll begin a course of treatments divided into the (a) intense early phase where we want to stop the active disease from progressing and recover as much of the lost vision, and (b) the second phase which is about maintaining that vision.
In the earliest years of these injections it used to start off with a monthly injection over one or two years or even longer, which can be rather challenging logistically and financially for many patients and their caregivers.
So, with the ALTAIR study, we found that we can divide the treatment into the intensive phase and maintenance phase. The intensive phase is where the injections are administered once a month for up to six months which can be daunting for many patients. Thereafter we can start to lengthen the duration between injections and the patients can breathe a little. We found that up to about half the patients only require treatments spaced about three to four months apart so it becomes much easier to maintain. And it is important that we maintain the injection schedule because if you don’t, the disease will recur and all the efforts that we have put in to prevent the disease from progressing, recover lost vision and maintain vision will be lost.
Q: What does a treatment entail?
The injection is administered into the eyeball which may sound daunting for many patients. However let me assure you that it is very safe. At the Singapore National Eye Centre, we administer over 10,000 injections annually and the safety record has been excellent and we take the necessary precautions to ensure that infection does not take root. Prior to the injection, the doctor administering the injection will apply numbing drops, and so that the patient does not see the needle coming, he/ she will be asked to look to the right, if the injection is coming from the left side of the eye. With adequate numbing eye drops patients may feel pressure on the eyeball but he/ she should not feel a needle-prick type of sensation.
Over time the injections can be administered over different areas rather than concentrated in the same area, but no stitches are required and the needle hole closes within 24 hours. The entire procedure takes about five minutes.
Q: What leads to a patient developing AMD?
Ageing is the main factor in the development of this disease so we never see this in persons under 50 years old. Having said that, not every aged person develops it. Additionally, there are a couple of important risk factors we know about and the most important and preventable factor is smoking. So, for someone who smokes, the likelihood of developing the disease is about three to four times higher; that has been shown in multiple researches. Apart from that, having a family history and certain genetic predisposition can increase one’s chances of developing AMD.
Q: There is also another subtype of AMD, also known as polypoidal choroidal vasculopathy or PCV. How is this related to AMD?
PCV is a chronic, degenerative eye disease that causes blurred vision or a blind spot in the centre of one’s visual field as a result of damage to the macula caused by abnormal blood vessels that form polyps (hence polypoidal) that leak fluid or blood. PCV is a genetic variant of AMD, the leading cause of severe, irreversible vision loss in people over age 60.
Vasculopathy is a general term used to describe any disease affecting blood vessels and polypoidal means relating to or resembling a polyp. The choroid, or choroid coat, is the vascular layer of the eye, containing connective tissues, and lying between the retina and the sclera. So polypoidal choroidal vasculopathy describes a condition where polyps develop in, or on, the blood vessels of the choroid.
PCV is also treated with the same injections as are used for wAMD, and again we start with an intensive phase of monthly injections but once the condition is stabilised we can extend the period between injections. Sometimes for the intensive phase of treatment the injections are given in combination with photodynamic therapy (PDT) treatment, a kind of laser treatment.
Q: How prevalent is PCV?
PCV is very prevalent among Asians, it makes up around fifty percent of AMD cases in East Asian populations. 50 percent of the AMD that comes through our clinics in Singapore have the PCV subtype. So in terms of how common it is in our adult population, it is only about 0.5% of the population. However, it increases with every 10 years as we get older, so it likely to become more common in 70 and 80 year olds.
Dr Cheung is Professor and Senior Consultant Ophthalmologist at Singapore National Eye Centre (SNEC), Duke-NUS Medical School, National University of Singapore (NUS), where she is also the is the Head of the Medical Retina Department.