Obesity and Glaucoma
Chat Highlights
June 18, 2008

On Wednesday, June 18, 2008, Dr. Michael Pro, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Obesity and Glaucoma".

Moderator: Welcome back to chat Dr Pro and chatters. This evening our topic is Obesity and Glaucoma. First, can you define obesity?

Dr. Pro:  Generally obesity is defined by body mass index (BMI). BMI is height divided by mass, but I do not have a specific number in the articles that I looked up. [The USA National Institutes of Health Heart, Lung, and Blood Institute defines normal BMI as 18.5-24.9, overweight as 25-29.9, and obese as greater than 30 – ed.]

P:  Is there really a connection between obesity and glaucoma? What percentage of patients would you say are obese?

Dr. Pro:  There is strong evidence that obesity is associated with elevated intraocular pressure, but so far nothing truly absolute as in many aspects of eye research. In terms of percentage of patients who are obese in the U.S., over 30% of the population could be in that category.

P:  Are there any studies done about which kind of glaucoma is affected more by obesity?

Dr. Pro:  The studies show a general relationship and generally imply POAG (open angle glaucoma). A relation between obesity and IOP was found in studies by Shiose et al., Klein et al, and Bulpitt et al., however those studies are now pretty old. Newer studies include a huge population study from Japan by Moria et al.

It is interesting that in the Japanese the IOP generally decreases with increasing age, something not seen in Western studies, but the study by Moria did show that IOP increased with increasing BMI. The study was a survey of 70,000 persons.

P:  Does the study in Japan indicate decreasing in IOP with age for obese patients as well?

Dr. Pro:  The increase in IOP in obese persons was shown to be independent of age.

P:  What kind of relationship was found in these studies? Was the IOP simply elevated, or was it elevated enough to cause glaucomatous damage or progression?

Dr. Pro:  It was really a sort of screening study; because it involved so many subjects, the data was collected and analyzed to see large patterns.

P:  Do glaucoma specialists routinely discuss weight with patients?

Dr. Pro:  I don't know if everyone does, but I usually mention exercise and weight loss to my patients as part of my discussions.

P:  What about someone like me with normal tension glaucoma, who never has had high pressures? Does obesity effect NTG pts?

Dr. Pro:  That's interesting, because these studies do not really tease out some of these subtle factors. It is notable that NTG is much more common in the Japanese, so the BMI data that I quoted may be relevant, but not every study has shown a relationship of BMI to glaucoma. Gasser et al. found no statistical difference in BMI between patients with glaucoma and control subjects.

Moderator: Thank you, Dr. Pro. Do you have any closing remarks on obesity?

Dr. Pro:  Well, let me add some ideas—IOP may increase due to excess intraorbital fat tissue, an increase in episcleral venous pressure, and a consequent decrease in outflow facility. Obesity increases blood viscosity through increasing red cell count, hemoglobin and hematocrit, and consequently increased outflow-resistance of episcleral veins results.

Episcleral venous pressure is the background innate pressure in the vascular system. The IOP cannot go lower than this pressure because the aqueous cannot leave the eye if the episcleral venous pressure is higher than the IOP.

It is also possible the IOP elevation may be an artifact; simultaneous breath-holding and thorax compression, with subsequent increase in venous pressure, may be a causative factor for transitory elevations of IOP.

Moderator: Dr. Pro, thank you once again for your time and valuable insights. Your work is greatly appreciated.

Dr. Pro:  Goodnight, and thanks.

On July 2, Dr. Pro discussed "Pediatric Glaucoma" in the Chat room. Click here for highlights of that meeting.

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