Diet is an important determinant of ocular health. In fact, a healthy diet is a key requirement for routine ocular function. Certain nutrients are essential for healthy vision and deficiency can lead to ocular dysfunction, disease and even blindness. Dry eye is a commonly encountered complaint in optometric practice, with about 38% of the general population affected. Notably, up to 40% of dry eye cases are moderate to severe, a cause of significant discomfort, reduced vision and even impaired quality of life. It is now well established that dry eye is driven by tear instability, and exacerbated by a number of environmental factors including contact lens wear, intense and prolonged visual tasks, smoking, central heating, preservatives in topical eye drops and importantly, an unbalanced diet.
The tear film is a complex microenvironment that helps maintain ocular surface integrity and comfort, protects from environmental exposure and infectious insult and provides a trophic environment for the corneal epithelium. Meibomian glands produce the lipid component of the tear layer which slows evaporation and aids tear stability, with meibomian gland dysfunction (MGD), a factor in a significant proportion of cases of dry eye.
The anti-inflammatory and antioxidant benefits of many nutrients are key to the long-term preservation of ocular health. Chronic inflammation and oxidative stress are the hallmarks of much age-related eye disease such as glaucoma, AMD and dry eye. In dry eye, these contribute to degradation in both the quality and quantity of tears, ultimately leading to chronic injury to the ocular surface. It is not surprising, therefore, that a healthy diet rich in antioxidant vitamins and minerals provides the best natural means to prevent, delay or even treat this type of ocular disease.
Ocular lubrication and lid hygiene are obvious ways to manage dry eye. However, they usually provide temporary relief and do not necessarily target the root causes of the problem. Dietary guidance along with targeted nutritional supplementation may offer a much better long-term solution that can significantly enhance patient outcomes.
Essential nutrients cannot be synthesised by the body and need to be sourced through a healthy diet, so that they can carry out a range of important functions in the eye. These include the omega-3 and omega-6 fatty acids which are of particular interest in the management of dry eye given their role in the production of meibomian secretions, anti-inflammatory effects and other properties. There is accumulating clinical data demonstrating a beneficial influence of omega-3 and omega-6 on tear stability, conjunctival inflammatory markers, signs and symptoms of ocular discomfort and tear evaporation rate.
The anti-inflammatory benefits of these fatty acids are critically dependent on their intake ratio. The optimal diet would include approximately equal quantities of both omega-3 and omega-6, but the modern diet is typically imbalanced in favour of much higher omega-6 intake (20 to 50 times higher than omega-3) due to increased consumption of processed foods and low consumption of fish. Instead of providing a potent anti-inflammatory influence, this imbalance can actually lead to increased inflammation and thereby contribute to dry eye disease.
Increased consumption of oily fish (e.g. just one portion of salmon or two portions of trout per week, baked or steamed rather than fried to preserve omega-3 content), coupled with decreased processed food intake could help redress this imbalance.
Of course, the recommended intake of those fatty acids can also be obtained from a high-quality dietary supplement for those who don’t like omega-3 rich foods. If you are going to recommend your patients a dry eye food supplement, here are a few important things to look out for:
- Where the fish was caught, is it an ecologically clean area?
- Is the supplement purified from pollutants and stabilised? (Highly unsaturated oils are very sensitive to oxidation). Quality marks are usually presented on the box (“quality silver”, “friend of the sea”, etc).
- Is the supplement blister-packed or is it loose in a jar? Blister-packed is preferable as it prevents oxidation of the active ingredients.
- Is the omega-6 to omega-3 ratio optimal, are there additional antioxidants in the formulation?
What can optometrists do to promote a nutritional and lifestyle approach to dry eye management?
As optometrists, we can increase the emphasis on preventative health in primary care practice and that process requires us to be better informed. The ophthalmic case history should explore every patient’s routine diet. We don’t have to wait for the patient to present with signs or symptoms of dry eye disease or something more sinister to respond with dietary guidance. We should be far more proactive with all our patients as the modern diet is often far from ideal, high in processed foods that are rich in calories but poor in nutritional content and can compromise long term ocular health. Reflecting the difficulty of initiating behaviour change in people with no manifest abnormalities, high-quality supplements can be stocked and recommended as a means of dietary fortification with nutrients that are not typically consumed in sufficient quantities. Indicators of nutritional status such as macular pigment levels can also be measured in practice and used to support dietary and supplement-based interventions. When disease does occur, the role of the diet and suitable supplements should become a priority. A more comprehensive, lifestyle-based approach to patient management that includes dietary guidance will be infinitely more beneficial to the long-term health of every patient we see.
