WHAT IT IS
This can be traced to a lack of tear production or an increase in tear evaporation.
An air-conditioned environment causes excessive evaporation of tears, as would poor eyelid closure, which can happen after cosmetic eyelid surgery, for instance, said Dr Jerry Tan,
a consultant eye surgeon at Camden Medical Centre. Long hours spent in front of a computer screen also causes people to blink less and this reduces lubrication of the eye with tears.
The tear film has three basic layers: oil, water and mucus. Problems with any of these layers can lead to symptoms of dry eyes. For instance, if the oil-producing meibomian gland in the eyelid is clogged, there would not be enough oil to coat the tear film, allowing it to evaporate more quickly, said Dr Por Yong Ming, a consultant eye surgeon at Mount Elizabeth Novena Specialist Centre.
Damage to the tear glands from inflammation can also hamper tear production.
Omega-3 and omega-6 fatty acids, when eaten together, have been shown to increase tear secretion slightly, said Dr Yong Shao Onn, a consultant at the NHG Eye Institute at Tan Tock Seng Hospital. They can also reduce symptoms in patients diagnosed with ocular surface disorders, such as dry eyes.
Omega-3 fatty acids reduce inflammation on the surface of the eye, preventing damage to the nerves, oil glands and tear glands of the eye.
Two omega-6 fatty acids - linoleic acid (LA) and its derivative, gamma-linolenic acid (GLA) - produce anti-inflammatory substances and are therefore beneficial to the entire body, including the lacrimal glands which secrete the watery component of tears.
Dr Tan said people should eat double the amount of omega-6 fatty acids as compared to omega-3.
Also useful is vitamin A, as this is needed by goblet cells, which secrete mucus, to work properly, said Dr Lee Hung Ming, medical director and senior consultant at Lee Hung Ming Eye Centre at Gleneagles Hospital.
A severe vitamin A deficiency can cause ulcers to form on the corneal surface and lead to xerophthalmia, a condition where the eyes fail to produce tears.
On the other hand, pregnant women should not consume excessive amounts of vitamin A, which can cause defective genes in their babies.
According to the Health Promotion Board, the recommended daily intake of vitamin A for a healthy adult is 750mcg. Half a cup (125ml) of carrot juice provides 966mcg of vitamin A.
Dr Por said a study showed that caffeine significantly increased participants' tear volume, compared with that of those in the placebo group who were given dextrose. This is why he tells his patients with moderate dry eyes to consume caffeinated beverages.
However, he would not recommend this method to people with heart disease or acid reflux, as they may get heart palpitations and stomach cramps.
Overall, a balanced diet helps in maintaining tear, conjunctival and corneal health.
Omega-3: Sardine, herring, mackerel, salmon (above), flaxseed, walnuts and linseed oil. Baking, stir-frying, steaming and poaching fish are preferred, to help preserve its omega-3.
Omega-6 (LA and GLA): Borage oil, blackcurrant seed oil and evening primrose oil.
Vitamin A: Carrot, sweet potato, spinach, pumpkin, tomato, mango, cod liver oil, animal (chicken, pork and beef) liver and cheddar cheese.
WHAT TCM SAYS
Dry eyes can result from one or more of these conditions: liver fire, which will dry up one's yin (the element responsible for cooling organs); "heaty" lungs; yin deficiency in the kidneys; and blood deficiency in the spleen.
Dr Tang Yue, a senior physician at Eu Yan Sang Premier TCM Centre at Paragon, recommended consuming food which can moisten the body, such as white fungus, bird's nest, raw rehmannia root and glossy privet fruit.
Other herbs which can promote vision include wolfberries and mulberry fruit.
AGE-RELATED MACULAR DEGENERATION
WHAT IT IS
This disease affects the central part of the retina, known as the macula, which is responsible for the sharp vision needed for tasks, such as reading and driving.
There are two forms of age-related macular degeneration (AMD).
Wet AMD, the more severe form, is characterised by bleeding and swelling at the macula due to the growth of abnormal blood vessels.
The dry form occurs when retinal pigment cells, which are crucial for vision, break down. It occurs in about 90 per cent of AMD patients.
The Age-Related Eye Disease Study (Areds), based in the United States and published in 2002, found that people who took high doses of vitamins C and E, beta-carotene and the minerals zinc and copper - called the Areds formulation - were 25 per cent less likely to progress to advanced AMD over a five-year period, compared with those who took a placebo.
These participants were already showing signs of moderate disease.
However, beta-carotene use has been linked to a heightened risk of lung cancer in smokers and there were concerns that the high zinc dose in the formula could cause minor side effects, such as stomach upset.
In 2006, a second study, Areds 2, was launched to find out if the original formulation could be improved on.
Researchers found that there was no additional benefit from adding omega-3 fatty acids or lowering the amount of zinc.
However, removing beta-carotene, which removed the risk of lung cancer in smokers, did not affect the efficacy of the formula.
Participants who had very little lutein and zeaxanthin (types of carotenoids) in their diets, but later took them in the Areds 2 formulation, which include lutein and zeaxanthin, were about 25 per cent less likely to develop advanced AMD than those on a similar diet who did not supplement it with lutein and zeaxanthin.
Dr Jerry Tan, a consultant eye surgeon at Camden Medical Centre, said lutein and zeaxanthin are good absorbers of excess blue light, which can cause oxidative damage to the retinal cells.
Zeaxanthin is mainly concentrated in the macula and may be more important than lutein in protecting the macula, added Dr Por Yong Ming, a consultant eye surgeon at Mount Elizabeth Novena Specialist Centre.
Lutein and zeaxanthin are types of carotenoids, which are the red, orange and yellow pigments found in many fruit and vegetables -
such as corn (left), spinach, kale, zucchini and broccoli - and egg yolk.
To promote their absorption, people should chop vegetables finely and cook them with little oil, said Dr Por. People above 50 years old with a strong family history of AMD can consider taking supplements containing lutein and zeaxanthin, he added.
WHAT TCM SAYS
The condition is linked to qi (vital energy) and blood deficiency in the liver, spleen and kidneys, said Dr Tang Yue, a senior physician at Eu Yan Sang Premier TCM Centre at Paragon.
When the kidneys grow weak due to ageing, they can be strengthened by herbs, such as Chinese wolfberries, mulberry fruit, tribulus and flastem milkvetch seed.
Boosting the kidneys can promote better vision because the kidney meridians - channels in the body through which qi travels - are located near the eyes, she explained.
WHAT IT IS
A cataract is formed when the lens of the eye, which is usually clear, becomes cloudy, blocking rays of light from entering the eye.
This makes images appear dim and blurred. Cataracts can be resolved by replacing the original lens of the eye with an artificial one. The risk of this condition increases with one's age.
Ageing eyes accumulate more by-products of normal chemical reactions in the eye, which can damage cells and cause cataracts to form, said Dr Jerry Tan, a consultant eye surgeon at Camden Medical Centre.
An abundant intake of fruit and vegetables, of more than three servings each a day, has been shown to reduce one's risk of cataracts by 10 to 15 per cent, he said.
Some fruit and vegetables contain vitamins and carotenoids which function as antioxidants, chemicals that counter certain oxidative processes in the eyes that damage the lens.
Vitamins B1 (thiamine) and B2 (riboflavin) have been found to help slow cataract formation, while vitamins B3 (niacin) and B9 (folate) reduce one's risk of cataracts, said Dr Tan. However, multivitamin supplements have to be taken regularly for up to several years, for one to reap the benefits, he added.
The production of coenzyme Q10 (CoQ10), an antioxidant in the body which helps to convert food into energy, diminishes with age, so replenishing it through one's diet "appears to be a logical method to help prevent cataracts", he said.
Vitamin B1 (thiamine): Yeast, yeast extract, pork, wholegrain cereals, animal liver and eggs.
About 25 per cent of thiamine in food may be lost during cooking. To preserve its content, food should be cooked in the shortest time possible and should not be soaked in water for too long, as thiamine is water-soluble.
Vitamin B2 (riboflavin): Yeast, yeast extract, milk, cheese, eggs, meat, fish, green beans, green leafy vegetables, wholegrain cereals and mushrooms. It is also used to colour food, such as ice cream, sauces and soups.
It can be degraded by prolonged exposure to light and also leaches into the water in which a food item is soaked.
Vitamin B3 (niacin): Tuna, chicken, turkey, mushrooms and salmon.
Vitamin B9 (folate): Green leafy vegetables, such as spinach, beans and peas, as well as egg yolk and liver.
Fresh leafy vegetables stored at room temperature may lose up to 70 per cent of their folate activity within three days, so eat them
fresh and do not overcook them.
CoQ10: Organ meat (heart, liver and kidneys). Smaller amounts are found in oily fish and whole grains.
WHAT TCM SAYS
Cataracts can be due to three underlying disorders, said Dr Tang Yue, a senior physician at Eu Yan Sang Premier TCM Centre at Paragon.
If the condition is due to qi-blood deficiency in the liver and kidneys - indicated by a sore back, fatigue and a frequent need to urinate at night - a person can take herbs, such as mulberry fruit, black dates, black beans and Chinese dodder seeds.
If the condition is due to a weak spleen that gives rise to a poor appetite, bloatedness and loose stool, then herbs, such as Chinese yam rhizome, white hyacinth bean, medicated leaven and hawthorn berries (above), can help.
If cataracts are due to a "heaty" liver - exhibited by a red face, dry mouth with a bitter taste and irritability - then opt for cassia seeds and tribulus, she added.