How Drug Abuse Affects the Eye
It's no secret that Americans are in the midst of a substance abuse crisis. According to the NIH, more than 33,000 Americans died from opioid overdoses in 2015 alone. (1) That same year, approximately two million Americans suffered from substance abuse disorders related to prescription opioid pain relievers, 591,000 from heroin use alone. (2) The cost can be devastating, but substance abuse is a modifiable lifestyle factor. As primary care physicians, optometrists can play a role in recognizing damage or dysfunction to either ocular structures or the components of the visual pathway these drugs cause and counseling patients in these circumstances.
This article reviews commonly used legal and illicit substances, and how each are associated with the formation, or exaggeration, of disease or damage.
The average cup of coffee or tea (in the United States) contains between 40mg and 150mg of caffeine. (3,4) Over-the-counter commercially available caffeine supplements contain between 100mg and 200mg per unit. (3,4) It is not until an individual ingests in excess of 5g of caffeine that toxicity is observed. (3)
Lid and cornea impact. Excess caffeine is associated with eyelid myokymia. (5,6) In animal models, during prenatal development ingested caffeine caused decreased total corneal thickness; it changed the thickness of each corneal layer in chicken embryos via changes in structure and the amount of collagen fibers. (7,8)
Caffeine consumption increases pupil size and amplitude of accommodation and can even dampen spontaneous pupillary oscillations up to six and a half hours after ingestion. (9)
Glaucoma. Although previous reports indicated that coffee consumption (and by extension, caffeine) raised intraocular pressure (IOP), more recent studies could not elicit a statistically significant change. (10-16) The rise in previous studies was likely secondary to water absorption. (15,16) In fact, more recent research lauds the potential use of caffeine to decrease ocular hypertension and attenuate neuroinflammatory responses, particularly in reducing the loss of retinal ganglion cells in ocular hypertensives. (17,18)
Posterior segment. Additionally, caffeine consumption is associated with decreased choroidal thickness at least four hours after ingestion. (19) Highly caffeinated energy drink consumption can cause intraretinal hemorrhages and acute loss of vision, which may be irreversible. (20) Similarly, excessive energy drink consumption can lead to transient macular ischemia via choroidal vasoconstriction, which causes bilateral central scotomas. (21) With the increased frequency of these types of occurrences, these retinal findings have been termed "coffee and donut maculopathy" or "energy drinkers' maculopathy." (22) With these ocular effects in mind, it is recommended that daily energy drink dosage should not exceed 400mg/day. (23)
The most commonly abused substance in the United States, alcohol accounts for 3.5% of deaths annually. (24,25) It should go without saying that excess consumption creates adverse effects which include liver cirrhosis, neurotoxicity and carcinogenesis. (25)
Macular degeneration. When it comes to ischemic heart disease, alcohol consumption has a J-shaped curve, meaning the dose-risk association shows a clear benefit in moderate drinkers but an increased risk as consumption increases to abusive levels. (25) That J-shaped curve applies to age-related macular...