Hypoxia’s Impacts on Visual Functions
Oxygen, being in the elemental group chalcogens and making up 21% of the atmospheric air, plays a vital role in sustaining the physiological processes of almost all living organisms. When oxygen is delivered to cells via the circulatory and respiratory systems, it stimulates cellular respiration in which it is utilized to make energy in the form of adenosine triphosphate (ATP). This same energy powers us to perform all of our daily activities, such as walking, exercising, and working. Of the hundreds of diseases that pertain to different regions of the human body, one particular condition that affects the body as a whole is hypoxia: a medical condition in which an individual has a low oxygen saturation (Merriam-Webster’s Collegiate Dictionary, 2020). Hypoxia has a negative impact on all areas of the body and results in symptoms such as changes in skin color, variations in heart rate, and muscle weakness. On top of these symptoms, hypoxia also affects the parts of the eye, impairing visual functions.
To understand why hypoxia has a disastrous impact on vision and other body parts, it is necessary to comprehend how oxygen is transported throughout the body and serves its normal function. Oxygen is inhaled through the nose and passes through the alveolar membrane and capillary endothelium to gain access to the bloodstream. In the bloodstream, 98.5% of oxygen is attached to a protein known as hemoglobin in red blood cells while the remaining 1.5% of oxygen is carried as a dissolved gas blood plasma. These oxygen molecules travel to each cell and combine with the glucose gained from food to make ATP, which serves as an energy source for the human body. As oxygen performs an important job in powering our daily activities, low levels of oxygen inhibit the proper function of body parts that require this energy to execute its tasks. Oxygen levels can be monitored through peripheral capillary oxygen saturation or commonly referred to as SpO2, which is an estimate of the oxygen content in the blood. More specifically, the SpO2 of a patient is the percentage of oxygenated hemoglobin compared to the total amount of hemoglobin in the blood. In normal individuals, SpO2 levels are at least 95% while in hypoxic patients levels range between 85% to 94%. When organs that regulate oxygen absorption and transmission are disturbed, many other organs are affected and have an inadequate supply of oxygen; for example, the eye.
Hypoxia also affects the cornea, transparent tissue at the front of the eye that covers structures including the iris and pupil. It controls the entry of light into the eye by refracting, or bending it. Because the cornea is transparent and can receive and bend light, it does not have any blood vessels. Therefore, its oxygen supply comes from the air present in the environment and is dissolved in the tears. Damage to the cornea due to hypoxia occurs primarily because of contact lenses since there is an artificial lens that prevents oxygen from entering the cornea. The cornea will then become less transparent and be unable to bend light, which negatively impacts the next parts of the visual process. This results in an impediment in visual function. To make up for the lack of oxygen, the sclera (the white tough tissue of the eye) can grow into the cornea, which results in scarring and a bloodshot eye. In addition, the retina may pump blood excessively and the eye may grow extra blood vessels to provide the cornea with nutrients and oxygen. It is best to avoid wearing contact lenses for long periods of time because hypoxia may ensue, causing corneal neovascularization and vision loss.
Even though hypoxia poses disastrous effects, such as visual impairment, receiving the appropriate treatment will increase oxygen levels and help someone living a normal, healthy, and happy life.
References
Merriam Webster. (n.d.). Hypoxia. In Merriam Webster. Retrieved from
https://www.merriam-webster.com/dictionary/hypoxia. (Accessed 2020–4–9)
Feenstra, D. J., Drawnel , F. M., & Jayagopal, A. (2018, April 18). Imaging of Hypoxia in
Retinal Vascular Disease | IntechOpen. Retrieved from
https://www.intechopen.com/books/early-events-in-diabetic-retinopathy- and-intervention-strategies/imaging-of-hypoxia-in-retinal-vascular-disease.
Photoreceptors. (2017, September 28). Retrieved from https://www.aao.org/eye-health/anatomy/photoreceptors.
Merriam Webster. (n.d.). Pathogenesis. In Merriam Webster. Retrieved from
https://www.merriam-webster.com/dictionary/pathogenesis. (Accessed 2020–4–9)
Healthline. (n.d.). Cornea Function, Definition & Anatomy | Body Maps. Retrieved from
https://www.healthline.com/human-body-maps/cornea.
Ophthalmic Partners. (n.d.). Corneal Neovascularization in Philadelphia, PA. Retrieved from
https://www.oppdoctors.com/corneal-neovascularization-philadelphia/.
Your eyes and oxygen. (n.d.). Retrieved from
https://www.oxygenworldwide.com/news/articles-and-information/635-your-eyes-and-oxygen.html.
Admesy. (2018, February 20). How Does the Human Eye Perceive Light? Photopic and Scotopic
Vision. Retrieved from https://www.azom.com/article.aspx?ArticleID=14971.
Glaucoma Research Foundation. (2019, December 17). Why Retinal Ganglion Cells Are
Important in Glaucoma. Retrieved from
https://www.glaucoma.org/glaucoma/why-retinal-ganglion-cells-are-important-in-glaucoma.php.
Vingrys, A. J., & Garner, L. F. (1987, June). The effect of a moderate level of hypoxia on human
color vision. Retrieved from https://link.springer.com/article/10.1007/BF00140454.
