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The 2019 National Coffee Drinking Trends report showed that 64 percent of people who participated in the survey said they had drunk coffee the previous day, which is interpreted as daily consumption. This was up from 57 percent in 2016, said the report. 

Even though the U.S. population is drinking more coffee than ever, the nation still only ranked 25th overall in per capita consumption. The people of Finland average 3 times as much coffee consumption as people in the U.S.

So what does all this caffeine intake do to our eyes?

The research is rather sparse and the results are mixed.

Here are some major eye topics that have been investigated:

Glaucoma

One study, published in the journal Investigative Ophthalmology and Visual Science, showed that coffee consumption of more than 3 cups per day compared to abstinence from coffee drinking led to an increased risk for a specific type of Glaucoma called Pseudoexfoliation Glaucoma.

Another analysis of several existing studies by Li,M et al demonstrated a tendency to have an increase in eye pressure with caffeine ingestion only for people who were already diagnosed with Glaucoma or Ocular Hypertension, but no effect on people without the disease. A separate study, published by Dove Press, done with the administration of eye drops containing caffeine to 5 volunteers with either Glaucoma or Ocular Hypertension showed that there was no change in the eye pressure with the drops administered 3 times a day over the course of a week.

Summing up the available studies in terms of Glaucoma, the evidence points to maybe a slight increase in Glaucoma risk for people who consume 3 or more cups of coffee a day.

Retinal Disease

A study done at Cornell University showed that an ingredient in coffee called chlorogenic acid (CLA), which is 8 times more concentrated in coffee than caffeine, is a strong antioxidant that may be helpful in warding off degenerative retinal disease like Age Related Macular Degeneration.

The study was done in mice and showed that their retinas did not show oxidative damage when treated with nitric oxide, which creates oxidative stress and free radicals, if they were pretreated with CLA.

Dry Eyes

A study published in the journal Ophthalmology looked at the effect caffeine intake had on the volume of tears on the surface of the eye. In the study, subjects were given capsules with either placebo or caffeine and then had their tear meniscus height measured. The results showed that there was increased tear meniscus height in the participants who were given the caffeine capsules compared to placebo. Increased tear production, which occurred with caffeine, may indicate that coffee consumption might have a beneficial effect on Dry Eye symptoms.

Eyelid Twitching

For years eye doctors have been taught that one of the primary triggers for a feeling of twitching in your eyelid has been too much caffeine ingestion (along with stress, lack of sleep and dry eyes). I have been unable to find anything substantial in the literature to support this teaching. Therefore, I’m going to have to leave this one as maybe, maybe not.

The End Result

Overall, the evidence for the pros and cons of coffee consumption and its effects on your eyes appear to be rather neutral. There are one or two issues that may increase your risk for glaucoma but it also may decrease your risk of macular degeneration or dry eyes.

Since there is no overwhelming positive or negative data, our recommendation is--and this holds for most things--enjoy your coffee in moderation.

What does blood in the back of the eye signify, anyway?

It could be a retinal vein occlusion, an ocular disorder that can occur in older people when the blood vessels to the retina are blocked.

The retina is the back part of the eye where light focuses and transmits images to the brain. Blockage of the veins in the retina can cause sudden vision loss. The severity of vision loss depends on where the blockage is located.

Blockage at smaller branches in the retinal vein is referred to as branch retinal vein occlusion (BRVO).  Vision loss in BRVO is usually less severe, and sometimes just parts of the vision is blurry.  Blockage at the main retinal vein of the eye is referred to as central retinal vein occlusion (CRVO) and results in more serious vision loss. 

Sometimes blockage of the retinal veins can lead to abnormal new blood vessels developing on the surface of the iris (the colored part of your eye) or the retina. This is a late complication of retinal vein blockage and can occur months after blockage has occurred. These new vessels are harmful and can result in high eye pressure (glaucoma), and bleeding inside the eye.

What are the symptoms of a retinal vein occlusion?

Symptoms can range from nothing to painless sudden visual loss. Sudden visual loss usually occurs in CRVO. In BRVO, vision loss is usually mild or the person can be asymptomatic. If new blood vessels develop on the iris, then the eye can become red and painful. If these new vessels grow on the retina, it can result in bleeding inside the eye, causing decreased vision and floaters – spots in your vision that appear to be floating.

Causes of retinal vein occlusion

Hardening of the blood vessels as you age is what predisposes people to retinal vein occlusion.  Retinal vein occlusion is more common in people over the age of 65. People with diabetes, high blood pressure, blood-clotting disorders, and glaucoma are also at higher risk for a retinal vein occlusion.

How is retinal vein occlusion diagnosed?

A dilated eye exam will reveal blood in the retina. A fluorescein angiogram is a diagnostic photographic test in which a colored dye is injected into your arm and a series of photographs are taken of the eye to determine if there is fluid leakage or abnormal blood vessel growth associated with the vein occlusion. An ultrasound or optical coherence tomography (OCT) is a photo taken of the retina to detect any fluid in the retina. 

Treatment for retinal vein occlusion

Not all cases of retinal vein occlusion need to be treated. Mild cases can be observed over time. If there is blurry vision due to fluid in the retina, then your ophthalmologist may treat your eye with a laser or eye injections. If new abnormal blood vessels develop, laser treatment is performed to cause regression of these vessels and prevent bleeding inside the eye. If there is already a significant amount of blood inside the eye, then surgery may be needed to remove the blood.

Outlook after retinal vein occlusion

Prognosis depends on the severity of the vein occlusion. Usually BRVO has less vision loss compared to CRVO. The initial presenting vision is usually a good indicator of future vision. Once diagnosed with a retinal vein occlusion, it is important to keep follow-up appointments to ensure that prompt treatment can be administered to best optimize your visual potential.