BACKGROUND OF THE DISEASE
Macular degeneration is an eye disease that has been the leading cause of visual disability and blindness in people aged 60 years in Europe and North America (Cook, Patel & Tufail, 2008). Worldwide, it is ranked third leading cause of blindness after glaucoma and cataract having led to 8.7% of all the legal blindness (Cook, Patel & Tufail, 2008). Macular degeneration is a condition encompassing the hyperplasia of the retinal pigment (RPE), drusen, choroidal neovascularization (CNV) and geographic atrophy. All these conditions are associated with the degeneration of the central portion of the retina (macula) where images are recorded and send to the brain for interpretation. Macula controls an individual's ability to drive a car, read, see objects in fine detail and recognize color or faces. Therefore, deterioration of this area as a result of macular degeneration leads to visual loss.
The macular disease is classified into two broad clinical categories; wet and dry. Wet macular degeneration is associated with the presence of abnormal neovascularisation whereas dry is associated with the atrophic type. To create a more elaborate understanding of macular degeneration, the paper examines in detail the diagnosis, symptoms, treatment and the current research on the disease.
People developing macular degeneration disease presents with a scotoma in their central retina. A scotoma is a blurry-like distortion which is rapid in onset neovascular condition or progressive in the geographic atrophy. Often, patients with vision loss occasioned by late macular degeneration in both eyes complain of hallucinations.
Clinically, patients with late macular degeneration have reduced visual acuity in the affected eye. The scotoma is mapped out by the patient using an Amsler grid. Also, an examination of the fundus using stereoscopic viewing may be preferred to detect the presence of exudative, pigmentary, drusen, atrophic or hemorrhagic changes affecting the macula.
Additional tests may be required during diagnosis to identify CNV. Fluorescein angiography may be used to ascertain the presence and assess the nature of neovascular macular degeneration. This process is accomplished by injecting sodium fluorescein intravenously. As the fluorescent dye fills the retinal and choroidal circulations, fundus photographs are taken. The photographs are taken through the barrier filter. CNV can be identified by its filling characteristics. CNV membranes fill with dye in the arterial phase and leak beyond the borders in later shots (Cook, Patel & Tufail, 2008).
When performing diagnosis of macular degeneration, however, some problems may be experienced. Some patients may develop visual hallucinations as clinical manifestations that would help in diagnosis, but many patients will not volunteer such symptoms unless the clinician is keen to directly ask them (Cook, Patel & Tufail, 2008). Also, patients who develop dry macular degeneration in both eyes may be asymptomatic making it difficult to suspect the disease. In such cases, diagnosis may be incidental during the routine optometric assessment (Cook, Patel & Tufail, 2008).
Symptoms of macular degeneration disease do not become easily apparent until late prognosis stages when treatment may not become effective. Common symptoms include gradual onset of dysmorphopsia, blurred vision, hemorrhagic RPE, scotoma, and neurosensory retinal detachment. The figure 1 below summarizes the symptoms and signs of macular degeneration disease. A scotoma is the loss of vision. Dysmorphopsia is the inability of the patient with macular degeneration to perceive objects correctly as a result of blurred vision (AOA, 2014).
Figure 1: Signs and symptoms of macular degeneration disease
Source: (AOA, 2014)
As shown in figure 1 above, signs and symptoms of macular degeneration vary according to different forms of the disease as well as the stages of prognosis. For instance, in late stages of the wet macular disease, a serious detachment of the sensory retina occurs with pigment epithelium hemorrhage, whereas in the dry late prognosis of the disease, geographic atrophy occurs with increased visualization of the underlying choroid.
Currently, there are some treatments for macular degeneration disease including the common laser photocoagulation and photodynamic therapy (PDT) as well as surgical methods. Conventional laser treatment, Argon laser photocoagulation is used to remove the area of active CNV in individuals with neovascular macular degeneration (Cook, Patel & Tufail, 2008). Photocoagulation potentially prevents severe loss of vision (Cook, Patel & Tufail, 2008). Conventional laser treatment is effective for patients with juxtafoveal classic no-occult CNV or extrafoveal CNV. Laser treatment will lead to dense scotoma in the area of treatment but it is minimized at the area of central vision to ensure that vision ability is not affected (Cook, Patel & Tufail, 2008).
Another common treatment is the PDT with Verteporfin. It involves a ten-minute intravenous infusion of Verteporfin to the affected area in the retina after which an application of diode laser (689 nm) follows. Photosensitizer molecules absorb light which initiates an oxidation process in protein and lipid membranes. Consequently, the cellular structures and thrombosis are disrupted which interferes with the vascular occlusion in active CNV (Cook, Patel & Tufail, 2008).
On the other hand, different surgical methods have been suggested as effective treatments including excision of choroidal neovascular membranes (ECNM) and retinal pigment epithelial cell transplantation (RPECT). In ECNM, a pars plana vitrectomy is performed to remove CNV through retinotomy incision. ECNM preserves retinal photoreceptors and allows an individual to regain his or her previous visual acuity. RPECT involves exogenous RPE transplantation and autologous RPE transplantation. In exogenous RPE transplantation, it is believed that poor visual acuity after CNV excision could be due to loss of RPE cells as part of the excised CNV. Thus, this surgical transplant introduces RPE cells to replace the lost ones and improve visual acuity. Autologous RPE transplantation is still restricted to research studies due to high complication rates (Cook, Patel & Tufail, 2008).
CURRENT AND NEW RESEARCH
Currently, although there are many recommended treatments of macular degeneration disease, there is more research to find new and more effective dry macular degeneration treatments. This follows the fact that treating dry macular degeneration disease has been elusive since the degeneration cannot be easily stopped or excised (NIHC, 2018). As the majority of the world population, especially in the US and Europe, heads to aging, more cases of macular degeneration are expected to occur. Therefore, more research in future will focus on effective treatments and prevention of the disease.
Macular degeneration is a serious disease causing blindness and loss of vision among elderly people. The fact that this disease affects elderly people and is currently ranked third cause of loss of vision raises worries amongst many people as the world's elderly population is increasing rapidly. It means that if more of the elderly people will be affected by the disease in as early as their age of sixty, they may lose their vision and become dependent on caretakers for the rest of their lives even if they have to live to 90s. It is likely that they will lead a poor quality life. Therefore, researchers have to put more efforts in the treatments and prevention methods.
AOA (American Optometric Association), 2014. Care of the Patient with Age-related Macular Degeneration [Internet]. Cited 02 March 2018.] Available from https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwj6qp38nJzaAhUJD8AKHbJABLsQFggnMAA&url=https%3A%2F%2Fwww.aoa.org%2Fdocuments%2Foptometrists%2FQRG-6.pdf&usg=AOvVaw3D_rxEFrW9fNiX1ueddfkM
Cook, H. L., Patel, P. J., & Tufail, A. (2008). Age-related macular degeneration: diagnosis and management. British medical bulletin, 85(1), 127-149.
NIHC (National Institute for Health and Care Excellence), 2018. Age-related macular degeneration: diagnosis and management [Internet]. [Cited 02 March 2018.] Available from https://www.ncbi.nlm.nih.gov/pubmed/29400919
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