Lifestyle and glaucoma

Patients with a family history of glaucoma are glad to be advised whether there is anything they can do to avoid glaucoma and those with glaucoma or ocular hypertension wish to know whether there is anything they can do to prevent deterioration.

In recent times a great deal has been learned about the effects of lifestyle on the development of cataract and of age-related macular degeneration (AMD),1 but there has been a paucity of information concerning lifestyle and glaucoma. It would seem unlikely that the tendency to develop primary open-angle glaucoma (POAG) is uninfluenced by external factors, but little has been identified. However, interesting information is now coming to light.

Cataract and AMD are both related to nutrition and to the environment, with many factors in common including poor diet, exposure to sunshine, and to smoking. Poor health commonly relates to lifestyle and many aspects of poor health such as poor education, poor nutrition,2,3 smoking4,5 cardiovascular disease,6 renal disease,7 and obesity,8 predispose to cataract. A number of factors may act together to increase the risk.9 The confirmation that cataract is related to poor health is that cataract is a predictor for reduced life expectancy.10 The environmental factor associated with cataract is exposure to sunshine11,12 and the incidence of cataract increases towards the equator.

Vitamins, particularly A (beta carotene), C and E have been shown to be protective to the macula13 and to the lens. The carotenoids and the essential fatty acid, Omega 3, have joined the vitamins as protective to the macula against AMD14 and to the lens against cataract.15

There are now known lifestyle factors relating to glaucoma:

Ginkgo

Ginkgo is supplied as a dried extract of leaves of the Ginkgo biloba tree which is anciently known to Chinese medicine and often cultivated in Britain for its ornamental value. The fossil record shows that it is a very ancient genus.

The eye is embryologically a part of the brain and so it is to be anticipated that any substance benefiting the brain would also benefit the eye. The beneficial effects of Ginkgo on the brain are directly from its action on neurones and indirectly from its action of blood flow. Ginkgo has been shown to enhance mental ability and to improve memory. Ginkgo has anti-oxidant and blood flow promoting properties.

The direct action on the brain is related to the anti-oxidant properties of Ginkgo. Ginkgo contains the flavanoids quercetin and myrecitin which give it significant anti-oxidant properties which protect body tissues from oxidative damage by free radicals. This effect has been shown in the protection of brain neurones. Ginkgo enhances blood flow by inhibiting platelet aggregation with reduction in blood viscosity.16 A significant increase in ocular blood flow velocity was demonstrated in glaucoma patients taking 120mg of Ginkgo extract a day.17

Field of vision loss in POAG is consequential to axonal death in the optic nerve. A major factor in this appears to be poor blood perfusion of the optic nerve head. This depends on the balance between the capillary perfusion pressure and the intraocular pressure, but axonal death can also occur in normotensive subjects with normal blood pressure. It appears that in these subjects the blood perfusion is unable to prevail against a normal intraocular pressure. A substance that improves blood perfusion would be expected to have a protective effect for the neurones and so to preserve the field of vision.

Ginkgo has the potential for protecting the optic nerve neurones both by its anti-oxidant activity and by promoting optic nerve blood flow. One study has shown that visual field damage is reduced in patients with normotensive glaucoma who are given Ginkgo.18 This has led to the recognition of the potential value of Ginkgo in the treatment of glaucoma.19,20,21

Ginkgo is not without risk to the eye and it has been implicated in causing orbital and ocular haemorrhage. It seems that this is more likely to occur in patients who are already taking anticoagulants such as aspirin and clopidrogel.22,23 Retinopathy is possible with excess Ginkgo intake.24

Ginkgo: conclusion

It is reasonable to recommend a Ginkgo supplement of 120mg a day to patients with low tension glaucoma and to POAG patients who have progressive field loss in spite of good pressure control.

Selenium

Selenium has previously enjoyed an immaculate reputation as a mineral for eye health and it has been usual to recommend a selenium supplement. The Reference Nutrient Intake (RNI), which is the UK standard, is 60 micrograms a day for women and 70 for men. A reasonable daily supplement has been considered to be 55 micrograms1 and the commercially available supplements for eye health commonly contain selenium. The Food Standards Association (FSA) recommends an upper limit of 450 micrograms a day as excess selenium is known to be toxic. Recently a high selenium intake has been identified as a possible cause of glaucoma.

Selenium is an essential mineral to the body. It is described as having anti-oxidant properties. This is because it provides the metal ion for antioxidant enzymes such as glutathione peroxidase and it has been considered to reduce the incidence of cancer. Natural sources of selenium include cereals, nuts, and especially Brazil nuts. Selenium is also present in sea foods and dairy products.

Anti-oxidants are considered important in retinal and lens health1 and have been considered as being possibly beneficial in reducing the probability of glaucoma11 because patients with POAG have been found to have reduced antioxidant activity in the anterior chamber.25,26 However, the long-term selenium supplementation study indicated that selenium may be a factor in causing glaucoma.27

The further study by Bruhn in the July 2009 issue of the British Journal of Ophthalmology28 has also implicated selenium as a possible cause of glaucoma. Subjects with POAG were compared with controls without POAG. However, this is a small study and the controls were patients presenting for cataract surgery and not therefore normals. The subjects with POAG were found to have significantly higher plasma selenium levels than in the controls. The explanation of an association between selenium and POAG may be that a high selenium level causes damage to the cells of the trabecular meshwork and impedes outflow.29

Selenium: conclusion

Selenium is essential for health. A large selenium intake may be a factor in causing glaucoma. Do eat well (including selenium rich foods) but minimise or avoid selenium supplementation. However, the jury is still out.

Marijuana

Marijuana, particularly in high dose, lowers intraocular pressure significantly in normals and in POAG.30,31 The mechanism of action has not been identified. Unfortunately the duration of action is short, 3-4 hours and marijuana also lowers blood pressure so that the optic nerve blood perfusion is likely to be reduced and the effect on glaucoma may be negative.

Marijuana: conclusion

It does lower eye pressure, but the effect is not useful and there are undesirable side effects.

Caffeine

Coffee causes an increase in the intraocular pressure in proportion to consumption. In normotensive subjects, in ocular hypertensives and in POAG subjects,

180mg caffeine in 200ml produces an elevation around 3mm at 90 minutes.32 Caffeine has been shown to be a risk factor in the development of POAG, but only in subjects with a family history of glaucoma.33

Caffeine conclusion

Drink coffee in moderation or change to tea, particularly if you have a family history of glaucoma.

Exercise

Physical exercise has a moderate effect in reducing eye pressure,34 while the retinal blood flow remains stable.35 Excessive exercise is not needed and a brisk walk for 20 minutes four times a week is sufficient. However, in about half of the subjects there is no reduction. The effects of regular exercise wear off in one month if exercise is stopped.34 The effect of exercise in preventing the development of glaucoma is not established.

Excessive exercise activities such as weight lifting raise the venous pressure and have a huge temporary effect in raising intraocular pressure36 (see below).

Exercise can have an adverse effect on eye pressure in those patients with pigment dispersion syndrome and with pigmentary glaucoma. In these patients, activities which cause head bobbing such as jogging can disperse iris pigment to clog the trabecular meshwork.37 Tight swimming goggles elevate the intraocular pressure in swimmers, which is significant in a swimmer wearing goggles for any length of time.

Exercise: conclusion

Moderate exercise has a beneficial effect on eye pressure, but is unproven in the prevention of glaucoma or in the prevention or deterioration of glaucoma.

Water

An excessive water intake reduces the blood osmolarity and thereby increases aqueous production. The water-drinking test was once in favour as a confirmatory test in patients suspected of being affected by what was then called chronic simple glaucoma. The patient was given 1 litre of water to drink in 10 minutes. A positive result was considered to be a rise in intraocular pressure of 8mm at 45-60 minutes.38 A positive result indicates that the patient has poor pressure autoregulation and is therefore prone to glaucoma.

A modern application of the water-drinking test in patients with established POAG on treatment has shown that the pressure increase is greater in patients with progression field loss than those without progressive loss.39 The rise in pressure on water drinking indicates lack of autoregulation which is understandable as a characteristic of persons liable to POAG and of persons with POAG liable to progressive field loss.

Water: conclusion

Avoid excessive water consumption.

Alcohol

Alcohol has a significant but temporary effect in reducing intraocular pressure.40 This may be by the diuretic effect of alcohol, or by action on the ciliary body in reducing aqueous secretion.

It might be considered that regular alcohol consumption would reduce the risk of developing glaucoma. However, alcohol consumers have not been found to have a reduced risk.41 Nor has alcohol consumption been found to be beneficial or harmful in patients with established POAG.42

Alcohol: conclusion

Alcohol is neither harmful nor beneficial. A useful effect in the treatment of raised ocular pressure would only be achieved by continuous alcohol consumption - not to be recommended!

Venous pressure

Raised orbital venous pressure increases the ocular pressure. This can be accounted for by impeded outflow from the canal of Schlemm and possibly also by a raised aqueous production rate. Non-pathological causes of raised venous pressure include a tight necktie.43,44

Straining at sport such as weight lifting has a huge effect in raising intraocular pressure. This is because the participant undertakes a breath holding Valsava manoeuvre with each strenuous lift. This raises the venous pressure.36

Venous pressure: conclusion

A tight neck tie and straining at sport raises ocular pressure, which may be best avoided, but is not confirmed as a risk factor for glaucoma.

Smoking

Smoking has an adverse effect on the circulation and is a factor in the development of several vascular eye disorders. It has clearly been established in the causation of AMD and in cataract1 and an adverse effect would be expected in glaucoma. Several studies have failed to show an association between smoking and the development of POAG,45 but the study by Bonovas shows that current smokers are at risk of glaucoma.46 It is logical that smoking is a risk factor for the deterioration of field of vision in patients with established glaucoma, but this does not appear to be significant.47

Smoking: conclusion

Smoking is implicated in AMD, cataract, glaucoma and much else. Don't do it!

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? Nicholas Phelps Brown is a consultant ophthalmologist based in Harley Street, London