Caffeine is found in coffee, tea, chocolate and some soft drinks. One study found that a cup of coffee has 107 mg of caffeine, one cup of tea has 34mg, and one glass of cola has 47mg, assuming all are caffeinated beverages. Another chart of typical caffeine content is shown below:
|1 mug of instant coffee||100mg|
|1 cup of brewed coffee||100mg|
|1 cup of instant coffee||75mg|
|1 cup of tea||50mg|
|1 can of cola||< 40mg|
|1 can of caffeine-containing “energy” drink||80mg|
|1 chocolate bar (100gm)||< 100mg|
|1 typical headache tablet||50mg|
Caffeine withdrawal can cause headaches and migraines which can result in visual symptoms such as temporary blind spots (scotomas), visual hallucinations or seeing spots in your vision. As caffeine is a vas0-dilator, it can affect the vessels in your eyes leading to many symptoms such as shifting vision and eye redness. Caffeine consumption has not been linked to an increase in eye pressure or glaucoma, although this has been suggested. If you consume too much caffeine, a ‘scintillating scotoma’ can occur causing the muscles in your eye start to spasm. It’s a temporary condition that lasts until your body metabolizes the caffeine. Long term the scintillating scotoma has no effect on vision.
Caffeine is classified as a central nervous system stimulant and diuretic (or urination promoter). Caffeine researchers Griffiths and Mumford examined the results of 37 studies conducted between 1833 and 1987, and found the following symptoms most often reported: headache (most common by far), drowsiness, decreased energy and alertness, increased work difficulty, decreased feelings of well-being and contentment, decreased sociability, friendliness, and talkativeness, flu-like feelings (muscle aches, stiffness, nausea), and blurred vision.
Coffee, especially caffeine has a bad reputation for vision practitioners. One reason is that coffee reduces nutrients in your eyes as well as your whole body. This is because coffee or caffeine is a diurretic that causes your body to rid of water and other nutrients in your body. This is because coffee causes the body to recycle less water and nutrients resulting to less absorption of water and nutrients. Hence, drinking coffee causes your body to eliminate water and nutrients faster than normal pace.
Caffeine may be effective in protecting the lens against damage that could lead to the formation of cataracts, according to a study presented on May 4 at the 2010 Annual Meeting of the Association for Research in Vision and Ophthalmology.
Researchers from the University of Maryland School of Medicine in Baltimore, MD hypothesized that caffeine may inhibit the intraocular generation of reactive oxygen species in the lens and consequent damage to the tissue.
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