Currently there is NO TREATMENT for AMD. Patients are simply advised to minimise the risk factors associated with AMD. These include stopping smoking, managing high cholesterol and blood pressure, reducing exposure to bright lights and taking nutritional supplements high in anti-oxidants. About 10% of AMD patients develop secondary complications that lead to formation and leakage from new blood vessels and this can cause sudden loss of vision. Anti-VEGF drugs now manage these complications effectively but this intervention does not alter the underlying progression of the disease.
Recent advances in research have provided a better understanding of the mechanisms underlying the development of AMD. It appears that the normal ageing process within the eye is considerably accelerated in AMD leading to the death of the visual cells of the retina.
For effective therapeutic intervention, the metabolic support to the retina needs to be improved. Scientists at AltRegen have demonstrated that compounds in ginseng extract can significantly improve the delivery pathways for providing nutritional support to the retina. Such an intervention is expected to slow the ageing process and thereby prevent the degenerative progress of AMD. This is the first viable treatment procedure for the prevention and treatment of AMD.
An ophthalmscope is used to view the back of a living eye and the typical features in the macular region of a normal eye are illustrated in the figure. A circular pale yellowish disc is the site of exit of the optic nerve. The blood vessels that supply two-thirds of the retina enter the eye through the optic disc and spread both on the surface and through the structure of the retina.
The macular region (shown as a dashed circular region) lies within the superior and inferior blood vessel "arcades". Within the macular region is a slightly depressed dark spot known as the fovea; this houses the highest density of photoreceptors and is used for discriminating fine detail.
Different layers of tissue lining the globe can be peeled away as shown in the figure. The thickest of these is the sclera and provides mechanical support to the eye. Lying on top of the sclera is the choroid, a tissue complex saturated with blood vessels providing metabolic support to the photoreceptor cells of the retina.
The retina is the innermost layer lining the inside of the eye and an enlarged, blue stained section is shown on the right in the figure. When isolated from a dark-adapted eye, the inner retina is transparent (allowing the transmission of light through it) whereas the outermost region is pinkish in colour due to the presence of the photopigment, rhodopsin.
Retinal nutrition is provided by a dual blood supply. The inner retina is supplied by blood vessels coming out of the optic disc and spreading on the surface and within the inner region. However, photoreceptors are supplied by the blood circulation in the choroid.
Rod and cone cells and information transfer in the retina. Light is detected by the photoreceptors and the information is passed on to other retinal cells in the inner retina for processing and final transmission via the optic nerve to the brain. There are essentially two types of photoreceptor cells, rods and cones, so named because of the shape of their light detection apparatus. In the human eye, there are about 120 million rods and 6-7 million cone cells.
Rod cells function optimally when light levels are low such as at night. As light levels increase, these cells become saturated and cannot contribute to visual function. Cone cells on the other hand operate in moderate to bright light and are therefore responsible for daylight vision. The intensity of light detected by rod or cone cells is transmitted to bipolar cells and these in turn pass on the information to the ganglion cells. However this basic information is processed by horizontal and amacrine cells so that not only is the detection of light by a given cell is registered but the amount of light in neighbouring cells is also included. The final signal sent to the brain is therefore very complicated but contains sufficient information for us to visualise our surroundings.
There are several types of cone cells, some responding to a limited range of wavelengths and others acting as motion detectors. The three major types are divided into red-, green-, or blue sensitive cones depending on the maximal absorption wavelength of light. In combination therefore, these cells allow us to appreciate the colours of the whole visual spectrum between 400-700nm.
In a digital camera, the resolution of the captured image is dependent on the pixel density of the detector. This is also true in the eye. If we know the density of photoreceptors in the eye, we can find the region that provides the greatest resolution. In the diagram below, the highest density of cone photoreceptor cells in found within the fovea, the region of highest resolution for daylight vision. The highest density of rod photoreceptors is also found in the macular region. Rod and cone densities fall away outside the macula. Thus in normal lighting conditions, the image obtained by the cornea and lens is focused on the macular region and for close-up work, on the fovea. If you focus on an object in front of you, then the image of the surroundings falls on the peripheral retina and it is very difficult to even recognise faces.
In diseases that lead to death of photoreceptors, the spatial density of these cells falls and therefore the image starts to degrade, commonly described as blurriness of vision. This is illustrated below where progressive loss of photoreceptors leads to blurred and unrecognisable images. In daily life, this would make it very difficult to read text and to recognise familiar faces. Further loss of photoreceptors would lead to blind spots and regions within the visual field of an individual patient.