Note from our Author
I have always had an interest in ophthalmology so I just took this opportunity to look into different eye diseases specifically Glaucoma because the last time we went to the eye doctor, my mom was tested for Glaucoma, and one of my teachers that I am close with also talked about how she knew she should test for Glaucoma because it ran in her family. As a result, I decided to research more on this topic to learn more about what Glaucoma really was.
Glaucoma
Background
Glaucoma is a neurodegenerative disease that causes the progressive death of retinal ganglion cells and their axons. “Glaucoma is the most common cause of irreversible blindness and the second cause of visual impairment after cataract worldwide. Nevertheless, over one-third of cases remain undiagnosed” (Nuzzi, 2020). Glaucoma is caused by damage to the optic nerve and a major risk factor for Glaucoma is eye pressure. It is frequently referred to as the "silent thief of vision" since it advances covertly and initially shows no symptoms.
Pathophysiology
According to Schuster et. al (2020), retinal ganglion cells are neurons in the central nervous system that receive signals from photoreceptors, process them, and transmit them to other centers in the brain on axons through the optic nerve. These axons run from the nuclei of the ganglion cells in the retina to the optic disc (2) and then, along with the retinal vessels, through the lamina cribrosa, a sieve-like structure made of collagen. Behind the sieve plate, the axons, surrounded by a myelin sheath, continue as the optic nerve. Elevated intraocular pressure, low perfusion pressure, and/or low CSF pressure increase the gradient across the cribrosa and cause papillary hypoperfusion, resulting in structural changes and remodeling of the cribrosa and impairment of axonal transport in the fibers of the optic nerve. The functional and anatomical damage caused by glaucoma is usually irreversible and the first visual field defects can only be detected with traditional perimetry when 40% of the ganglion cell fibers have already been damaged (in the case of necrosis or apoptosis), early detection (Nuzzi et.al, 2020). In open-angle glaucoma, the pores in the anterior region of the lamina cribrosa are enlarged. The growing loss of ganglion cells of the retina leads to a progressive deterioration of the visual field, which usually starts in the middle of the half and then progresses until only a central or peripheral island of intact vision remains. This leads to a decrease in the normal intraocular pressure. “The normal intraocular pressure has an average value of 15.7 mm Hg” (Schuster, 2020). It is controlled by the balance between the secretion of the aqueous humor by the ciliary body and its outlet flow. The impact of normal intraocular pressure is different for each type of glaucoma (Chan, 2018).
Open-angle glaucoma
The classification of glaucoma is based on the occurrence and obstruction of the outflow pathway and whether it is primary which is the most common or associated with detectable comorbidity, (secondary glaucoma). and restricted aqueous humor flow associated with increased intraocular pressure (IOP), ie hypertensive glaucoma (Cvenkel & Kolko, 2020). “Due to this blockage, the pressure in the eye gradually increases, resulting in damage to the optic nerve and progressive visual loss. Secondary open-angle glaucoma can have multiple etiologies but is far less common than primary open-angle glaucoma (Foris & Tripathy, 2021). Open-angle glaucoma can be clinically evaluated using a variety of diagnostic tools but the following triad has been the cornerstone of diagnosis: Optic disc changes, Visual field changes, and Elevated intraocular pressure. Optic disc changes. For the optic disc changes, when an examination revealed an increased cup-disk ratio (CDR), CDR asymmetry, disc hemorrhage, or elevated intraocular pressure, there is a high risk for Glaucoma. Visual field changes show if one has glaucoma if that maps out the patient's visual field on a printout. For the elevated intraocular, if a difference of 3 mmHg or more is noted between the two eyes, there should be an increased suspicion for the presence of glaucoma. This is important as this helps with early diagnostics where medication, therapy or drops could be used to help relieve and reduce the progression of Glaucoma (Foris & Tripathy, 2021). All these treatments are surrounded by decreasing intraocular pressure. In patients with open-angle glaucoma, the intraocular pressure can be reduced with regularly applied eyedrops, laser therapy, and/or surgery, and tropical treatment (Schuster et al., 2020).
Treatment
There is no cure for glaucoma but treatment if the disease is diagnosed at an early stage can stop the damage and protect one’s vision. The only proven treatment strategy for glaucoma is to lower intraocular pressure (IOP). However, despite controlled IOP, some patients experience progressive loss of visual field and quality of life, indicating that other factors are involved in glaucoma. As a result, approaches that do not rely on IOP lowering to prevent or slow progression has been a necessity in research (Cvenkel & Kolko, 2020). In recent times, in order to tackle this problem and find an alternative treatment that slows progression, the interest in neuroprotective agents has arisen as they have learned that glaucoma doesn't only affect the retinal and axon fibers of the optic nerve but affects the brain (Nucci, 2018).
Memantine is a noncompetitive NMDA receptor antagonist which is used to treat Alzheimer's and Parkinson's disease. Memantine protected against retinal ganglion cell loss in animal glaucoma models. Unfortunately, in two large clinical trials, daily memantine treatment for four years did not prevent or delay progression in patients with open-angle glaucoma and was no better than placebo (Cvenkel & Kolko, 2020). This increases the need for research in this field as there is no cure for a disease that has impacted millions of people worldwide. In addition, there is no treatment for people diagnosed with glaucoma at a later stage of the disease. In addition, the treatment approach that has been used is shown to not be the most effective method for all people with glaucoma. Without increased research, many more people will be at high risk of losing their visions forever.
Conclusion
If undiagnosed and untreated, glaucoma is a serious eye ailment that can steal one's vision silently. Individuals can protect their eye health by taking preventative measures if they are aware of the types, risk factors, symptoms, and available treatments. Glaucoma management and maintaining one's priceless gift of sight require regular eye exams and adherence to prescribed treatment regimens. By spreading knowledge about glaucoma, we can promote early detection and treatment, ultimately aiming to lessen the burden of this condition that can cause blindness.
References
Barbosa-breda, J., Van keer, K., Abegão-pinto, L., Nassiri, V., Molenberghs, G., Willekens, K., Vandewalle, E., Rocha-sousa, A., & Stalmans, I. (2018). Improved discrimination between normal-tension and primary open-angle glaucoma with advanced vascular examinations - the leuven eye study. Acta Ophthalmologica, 97(1), e50-e56. https://doi.org/10.1111/aos.13809
Chan, K. K. W., Tang, F., Tham, C. C. Y., Young, A. L., & Cheung, C. Y. (2017). Retinal vasculature in glaucoma: A review. BMJ Open Ophthalmology, 1(1), e000032. http://dx.doi.org/10.1136/bmjophth-2016-000032
Cvenkel, B., & Kolko, M. (2020). Current medical therapy and future trends in the management of glaucoma treatment. Journal of Ophthalmology, 2020, 1-14. https://dx.doi.org/10.1155%2F2020%2F6138132
Mahabadi N, Foris LA, Tripathy K. Open angle glaucoma. [Updated 2022 Feb 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441887/
Nucci, C., Martucci, A., Giannini, C., Morrone, L. A., Bagetta, G., & Mancino, R. (2018). Neuroprotective agents in the management of glaucoma. Eye, 32(5), 938-945. https://dx.doi.org/10.1038%2Fs41433-018-0050-2
Schuster, A. K., Erb, C., Hoffmann, E. M., Dietlein, T., & Pfeiffer, N. (2020). The diagnosis and treatment of glaucoma. Deutsches Ärzteblatt International. https://dx.doi.org/10.3238%2Farztebl.2020.0225
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