As the healthcare system advances, one of the most essential factors in prognosis for a medical condition is early detection and treatment. While this can be done for many diseases, it is still difficult to identify the early stages of glaucoma, an eye condition that is the leading cause of blindness worldwide (Tham et al, 2014). Early detection is vital since symptoms do not usually appear in the early stages of open-angle glaucoma and, if the condition is not treated early enough, the damage can cause irreversible vision loss (Lemzi, 2007).
In order to understand possible detection methods, it is essential to discuss the mechanism of the disease. Glaucoma is a condition defined by degeneration of the optic nerve (Almasieh et al, 2012). This damage occurs in retinal ganglion cells, a type of neuron in the central nervous system with nerve fibres connecting the brain and retina (Almasieh et al, 2012). Without the optic nerve properly passing electric impulses from the eye to the brain, the quality of vision decreases (Abdelkader, 2016). This optic neuropathy occurs as a result of the buildup of a fluid in the eye called the vitreous humour (Figure 1) (Lemzi, 2007) which increases pressure in the eye, damaging the optic nerve (United States National Institute of Health, 2018).
It is widely accepted that the retinal ganglion cells then undergo apoptosis. Since they are nerve cells, they do not regenerate, causing permanent nerve damage (Almasieh et al, 2012). Given that primary vision loss with glaucoma affects mainly the peripheral vision (Figure 2), it is difficult to detect early symptoms (Thylefors and Négrel, 1994).
One of the hurdles many ophthalmologists face when attempting to diagnose glaucoma is that many of the tests are inherently flawed (Lemzi, 2007). Typically, medical professionals would measure intraocular pressure (IOP) as a warning sign of glaucoma (Lemzi, 2007).While increased fluid pressure in the eye may indicate an individual is at risk for glaucoma, intraocular pressure varies widely within a population, so it is not an accurate test for diagnosis (Lemzi, 2007). Another common test for glaucoma is a field test measuring peripheral vision; multiple tests are often required to gain a result, and there are often fluctuations between measurements, which hampers accuracy (Lemzi, 2007).
One of the more promising methods for diagnosis of open angle glaucoma is optical coherence tomography (OCT) (Adhi and Duker, 2013). This technique uses low coherence light (Huang et al, 1991), which is light that does not have a constant phase difference between multiple waves (Flores-Domínguez, Ochoa-Valiente, R. and García-Trujillo, 2015). This technology generates cross-sections showing different layers of a patient’s retina and the retinal nerve fibre layer (RNFL) (Adhi and Duker, 2013) (Figure 3). The latter measurement is essential since studies show that the RNFL is significantly thinner in patients with glaucoma, and that thinning of the RNFL typically precedes any loss of vision (Bowd et al, 2000). This means that OCT is particularly useful for patients who are in earlier stages of glaucoma because they could be treated before optic nerve degeneration becomes severe (Angeles and Chopra, 2017).
However, like any medical tests, there are downsides. Once the RNFL becomes too thin, any further deterioration cannot be measured, and researchers note that there are still limitations (Angeles and Chopra, 2017). While it is promising to see scientific improvements in testing for such a widespread condition, the progress that has been made must continue. Current estimates project that the number of glaucoma patients will increase from the current sixty million, to over one hundred and eleven million by 2040 (Tham et al, 2014), so research in this field is a necessary investment in the future.
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