Alcohol is one of many psychoactive drugs with addictive potential, which has a significant impact on public health and individuals in society (Crocq, 2007). Alcohol is a modifiable lifestyle factor that has intentionally inflicted and unintentionally acquired injuries (Iranpour and Nakhaee, 2019, p. 132) that has resulted in hospitalization and is most widely used as a recreational drug in the Western world. The health of the eye is important because there is a co-dependent relationship between the eyes and the brain. Alcohol consumption can cause anomalies of the central nervous system (CNS), including the brain, and lead to a wide spectrum of ocular deformities (Stromland and Pinazo-Duran, 2002). Further studies have shown alcohol ingestion results in a varying degree of consequences regarding vision and eye health such as impaired eye coordination, blurry vision, cataracts (Silva et al., 2017). This essay will discuss the effects of alcohol on the health of the eyes. More specifically the essay will touch upon certain ocular diseases or conditions that are triggered by the consumption of alcohol, which include fetal alcohol syndrome (FAS), visual impairment, impairment of rod and cone photoreceptors and age-related macular degeneration (AMD).
Fetal Alcohol Syndrome (FAS)
Fetal alcohol syndrome begins with maternal alcohol consumption during pregnancy. This later leads to many anomalies of the central nervous system (CNS) and a wide spectrum of ocular deformities (Stromland and Pinazo-Duran, 2002). A retrospective study by Hug et al., (2000) looked at 11 children who had been diagnosed with fetal alcohol syndrome (FAS). Magnetic resonance imaging (MRI) and ophthalmologic exams were conducted, and it was found that all participants tested had abnormal magnetic resonance imaging results (Hug et al., 2000). Optic nerve hypoplasia was found in 91% of the subjects during the ophthalmology exam (Hug et al., 2000). Optic nerve hypoplasia is a condition whereby the optic nerves are underdeveloped (National Organization for Rare Disorders, n.d.). Alcohol exposure can damage the optic nerve and the retina by altering glial cells and degenerating myelin sheath, ganglions, and optic axons (Pinazo-Duran et al., 1997). These findings suggest that early pregnancy alcohol exposure affects the development and the health of the fetus's eyes. Stromland and Hellstorm's (1996) study of 25 children with fetal alcohol syndrome, which reported a finding of 76% occurrence of optic nerve hypoplasia in their subject's ophthalmology exam results is significantly lower than Stromland (2002) study. Since Hug et al., (2000) finding was conducted on small sample size (11 children), the retrospective study can be repeated on a larger sample size, to determine the accuracy of Stromland and Hellstorm's (1996) study, however there might be other reason for this difference, which might be worth exploring by Hug et al., (2000). Overall, FAS is important both in terms of its prevalence and its effects. The eye is a sensitive, yet accurate marker that serves as a helpful diagnosis for FAS, and many women will not admit to excessive drinking while pregnant. For several reasons, diagnosing FAS at birth may be difficult. There are no laboratory tests to show FAS, so finding the usual signs and symptoms such as underdeveloped optic nerve and damaged retina alongside finding a history of drinking during pregnancy is the only way to diagnose FAS. Treatments could be offered for more serious conditions when it has been detected earlier on (Chicago Medicine, n.d.). In conclusion, FAS is important both in terms of its prevalence and effects, this goes to show how it can have a detrimental effect on the fetus’s eye health.
Visual Impairment
One of the main causes of accidents is down to excess alcohol consumption. Consumption of a large quantity of alcohol can cause visual impairment, this leads to a decreased field of vision and an increase in saccadic eye movement. Saccadic eye movements are rapid eye movements which carry the image of a subject to the fovea (Wong, 2014). A study conducted by Marinkovic et al. (2013), showed that 22 healthy social drinkers were participated to functional magnetic resonance imaging (fMRI) which scanned and monitored eye movement when the participants were under the influence of alcohol. Visually guided prosaccades were used to move towards a target and volitional anti-saccades to move away from it (Marinkovic et al., 2013). The study shows that the consumption of alcohol can impair top-down function. This decreases control and increases saccadic eye movement, and results in a weak anterior cingulate cortex (ACC). The anterior cingulate cortex (ACC) is an important part of the human mediofrontal neural circuit it monitors the cognitive system's brain activity for any indications of error (Ridderinkhof, 2002). When the anterior cingulate cortex is weakened the communication between the optic nerve and the brain is slowed, thus delaying communication between the eye and the brain, and therefore affecting the individual's ability to make decisions (Marinkovic et al., 2013). It is noteworthy that the results of the ACC's sensitivity to saccadic conflict and error processing in the Marinkovic et al. (2013) study are consistent with other fMRI studies (Ford et al., 2005). In conclusion, since consumption of a large quantity of alcohol can cause visual impairment, which can affect decision-making, it is fair to say that any form of impaired vision can endanger other drivers on the road. Therefore, by optometrists or healthcare professionals recognizing visual impairment in drivers, traffic safety precautions can be guaranteed (Hartung et al., 2020).
Impairment of Rod and Cone Photoreceptors
The visual processing system can detect a wide spectrum of light: between daytime and night-time (Olympus Life Science, n.d.). Rod cells are responsible for night vision (scotopic vision), whilst cone cells can absorb a broad range of light particles and are therefore responsible for color vision (photopic vision) (Kenhub, 2020). According to the findings of a present study, at mesopic light levels, small consumption of alcohol can impair both cone and rod functions (Zhuang et al., 2015). This was addressed in Zhuang et al. (2015) study, which measured the critical flicker frequency (CFF) before and after the consumption of excess alcohol (0.8kg) in social drinkers, which was later compared with the placebo beverage (control). The social drinkers' primary visual stimuli: cone, rod, and a mixture of both were measured under three light conditions: medium light intensity, low light intensity, and dim light intensity- this was done using the CFF test (Zhuang et al., 2015). In a CFF test, the frequency of the light is altered over time, and the patient is expected to describe the highest frequency at which they can still observe the light as 'flickering' (Bajaj, 2012). The results proved that alcohol had a significant impact on the CFF values of (cone, rods and, both), at all light intensity levels when compared to the control (placebo beverage) (Zhuang et al., 2015). Zhuang et al. (2015) study showed that an excess dose of alcohol impacted temporal processing, which is mediated by the magnocellular pathway - which is where rod and cone cells are mediated. The findings are consistent with a previous study done by Zhuang et al. (2012), who found that alcohol intake reduced the contrast sensitivity in the magnocellular pathway (Zhuang et al., 2015). Therefore, consumption of alcohol can impair both cone and rod functions, however, further research may be needed to determine if the impairment of rod and cone photoreceptors by alcohol, increases the risk of any rod and cone related ocular diseases such as progressive cone dystrophy.
Age-Related Macular Degeneration
Increased alcohol consumption increases the risk of age-related macular degeneration (AMD). Age-related macular degeneration is a common condition, amongst individuals over the age of 50 (NHS, n.d). It causes vision loss in the central view, but not complete blindness (NHS, n.d.). A study, conducted by Adams et al. (2012), reported that an increased risk of late AMD was associated with heavy drinking. Adams et al. (2012) study used 20,963 participants, aged 40-69, to investigate the correlation between alcohol consumption and AMD prevalence. A formal interview at the start of the study was used to assess participants' alcohol intake at baseline (1990-2007). Then from 2003 to 2007, digital macula images of both eyes were collected and evaluated for any indication of early and late AMD (Adams et al., 2012). The results showed that alcohol consumption of 20g or more a day significantly correlated with a 20% increase in the likelihood of contracting early AMD, compared to the results for late AMD. These findings indicate that there is a clear correlation between alcohol consumption and an increased risk of AMD. Majority of previous studies (Arnarsson et al., 2006; Knudtson, Klein and Klein, 2007; Varma et al., 2004) have reported findings of increased risk of late AMD when alcohol consumption is in excess (less than 40g a day) and a significant correlation between drinking and early AMD (Adams et al., 2012). Adams et al. (2012) study findings not only suggest that excess alcohol consumption is detrimental to eye health, but alcohol levels that are deemed 'moderate' or 'social' also increases the likelihood of contracting early AMD. In conclusion, limiting the intake of a large volume of alcohol per day could significantly slow down the rate an individual develops age-related macular degeneration. Alternatively, individuals should attend their annual eye examinations with the eye healthcare providers such as optometrists. This will enable the healthcare providers to detect any abnormalities to the retina and macula, and thus start treatment at its earlier stage.
Conclusion
In summary, this essay has discussed the effects of alcohol on the health of both eyes. Excess alcohol exposure can have a long-term effect on the fetus’s eyesight, including underdevelopment of the optic nerve (optic nerve hypoplasia). Similarly, the long-term implications of age-related macular degeneration rise with increased alcohol intake and alcohol affected ACC can lead to visual impairments. However, the short-term effects of acute alcohol consumption affected both cone and rods function at mesopic light levels.
References
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