Geography
atrophy (GA) is a chronic disease, which leads to visual function loss. It is
defined as a round or oval area of atrophy of 175 µm or more. It is the last
stage of dry age-related macular degeneration (AMD) that can result in the
progressive and irreversible loss of retina.
The
initial symptom of GA may be found during reading, when one or several letters
in a word are missing, or when looking at faces, a small part of the face
cannot be seen. Some risk factors of GA are family history of AMD, smoke and
increasing age.
GA
is classified in two types drusen-related GA and neovascularization-related GA.
Drusen related GA is the hallmark of ADM: it is seen as crystalline yellow or white
dots that lie between the retinal pigment epithelium and membrane whereas the
neovascular process leads to a plethora of cellular stresses such as ischemia,
inflammation and dramatic changes in cell environment that further taxes
retinal pigment epithelium cells already dysfunctional from drusen-associated
changes.
According
to study, “Geographic Atrophy - Pipeline Review, H2 2018” some
of the major companies that are currently working in the geographic atrophy are
Achillion Pharmaceuticals Inc, AcucelaInc, Alkeus Pharmaceuticals Inc, Allergan
Plc, Apellis Pharmaceuticals Inc, Cell Cure Neurosciences Ltd, Colby
Pharmaceutical Co, F. Hoffmann-La Roche Ltd, Foamix Pharmaceuticals Ltd,
Genentech Inc, GenSight Biologics SA, Ionis Pharmaceuticals Inc, Johnson &
Johnson, Novartis AG, NovelMed Therapeutics Inc, Ophthotech Corp, Ra
Pharmaceuticals Inc.
There
are some diagnostic procedures are involved in GA, which are;
autofluorescense,optical coherence tomography (OCT), multifocal
electroretinography and ordinary measuring. Autofluorescense is an imaging
technology to visualize the retinal pigment epithelium (RPE) in geographic
atrophy: itprovides important information on expected progression rate through
the amount of hyperfluorescense in the functional zone of the lesion.OCT can
help early recognition of intraretinal fluid, which is important in order to
start treatment and remain function. The atrophy of the retinal layers becomes
very obvious by OCT technique. In multifocal electroretinography, a light
stimulus is performed in patterns across the retina, and photoreceptor
signaling is detected by an electrode. Ordinary measuring provides poor
information on the actual function of the retina, due to foveal sparring and
parafoveal scotomas, therefore microperimetry tools is used to evaluate all
functions.
There
is currently no proven treatment for GA. Patients can benefit from increased
lighting, magnification and low vision devices that help with reading. However some
medication involved for GA includes nutritional supplementation formula,
neuroprotection and vasodilators. Nutritional supplementation formula consist
by 80 mg zinc oxide, 2 mg cupric oxide, 15 mg β-carotene, 500 mg vitamin C and
400 IU vitamin En the different stages of AMD. In neuroprotection, two main
drugs are used: brimonidine and ciliaryneurotrophic factor-501.In vasodilators,
alprostadil, MC-1101, moxaverine and sildenafil drugs are used for treatment of
GA. Some other drugs are underway in the treatment of GA for instance emixustat
and fenretinide. Additionally, cell based therapy and APL-2 injections are also
used for treatment of GA. Moreover, an implantable miniature telescope is also
used for treatment of GA.
Nowadays
there are two strategies are being explored to prevent the GA: photoreceptor
& RPE preservation and inhibition of the complement cascade. Photoreceptors
and the RPE are used to devise agents that ensure adequate circulation to the
choroidal vasculature, thereby preventing apoptosis secondary to ischaemia.
Lampalizumab is a monoclonal antibody fab fragment that inhibits complement
factors and improves the efficacy of eculizumab in reducing the progression of
GA AMD.
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