Dry Eye – The Optometrist’s Perspective
Koh Lian Buck, BSc(Hons) Optom UK
To the optometrist, Dry Eye Syndrome (DES) is probably the next most common problem we see other than examining refractive errors in patients’ eyes. Be it young or old, contact lens wearers or not, we often hear our patients complain of symptoms such as burning and/or tearing (early symptoms), stinging, itching or grittiness, dryness, redness, heaviness of lids, photophobia, excessive mucus, and ocular fatigue. The definition of dry eye was adopted by the International Dry Eye Committee (DEWS) in 2007 as “A multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance, and tear film instability with potential damage to the ocular surface”
This article highlights and reminds us of the fundamentals behind dry eye: its causes, diagnosis and management of the problem within the context of an optometric practice.
The Pre-Corneal Tear Film
The pre-corneal tear film maintains the health of the ocular surface. It is the primary source of nutrients like oxygen for the cornea and it removes wastes like carbon dioxide from it. It is also the first line of defense against bacteria and it keeps cells moist and prevents its breakdown. The other important functions of the tear film are the preservation of clear vision by providing a smooth optical surface; and hence ensure comfort as the eye lids sweeps across the cornea through the lubricious ingredients found in the tear film. Hence a breakdown in the pre-corneal tear film will result in dry eye symptoms
Causes of Dry Eye
Two main mechanisms are well known to cause dry eye; increased evaporation and decreased tear production. The most common cause of increased evaporation from the eye is meibomian gland disease, whereby there is a reduced delivery of oil to the lid margin and to the tear film. Blepharitis, meibomian gland disease, and other lid abnormalities can cause evaporative tear loss. At the same time, reduced blink rate, area of palpebral aperture and unfavorable environmental conditions are contributing factors to dry eye, despite normal lacrimal function.
Aging of the population and the co-occurring diseases have a large effect on tear production and ultimately leading to dry eyes symptoms. Patients with systemic conditions like rheumatoid arthritis, SjÖgrens syndrome, and thyroid diseases are at risk of DE. Similarly, medications like antihistamines, decongestions, diuretics, beta-blockers, anti-depressions, anti-anxiety, hormone replacement therapy, oral contraceptives can also cause DE. In a Lasik surgery, the creation of the corneal flap severs almost all nerves on the surface of the cornea. Such nerves provide feedback to the lacrimal glands; so it is predictable that post Lasik patients experience DE symptoms as least in its initial stages until nerves regrow on the affected areas.
Contact Lens and Dry Eye
The presence of a contact lens with a thickness of almost 10 times that of the pre-corneal tear film can certainly disrupt the tear film, affect the tear physiology and increase the rate of evaporation and further decrease the tear break-up time. Lens related dryness is a significant problem affecting short and long term success with contact lens wear. Unlike non-contact lens wearers, lens related dryness experienced by wearers are not gender biased; and late day dryness symptoms are more frequent and intense compared to non-CL wearers. Although there have been advancement in lens materials, surface properties and edge designs, Dryness being cited as the reason for CL drop out remains high.
Diagnosing the Dry Eye Patient
Besides listening to the patient’s symptoms that may suggest DE, clinical signs which ECPs should look out for include reduced tear breakup time (TBUT), hyperemia, absence or reduced tear meniscus, increase tear debris, epiphoria (excessive tearing), corneal staining and blepharitis and/or meibomian gland disease. The use of a slit lamp is indispensable in the detection and clinical diagnosis of DE. Fluorescein dye is used commonly to measure TBUT and to reveal any corneal staining. The pattern/ type of staining will help differentiate between DE related or from other pathological etiology like toxicity or infectious keratitis. Table 1 shows the various tools that may be used to diagnose DE.
Figure 1. Various diagnostic tools used to evaluate and measure dry eye syndrome.
Since part of the early symptom of DE is reflex tearing, there may be instances where ECP may misdiagnose the tearing as some form of allergic reaction and hence prescribe anti histamine medications; hence potentially exacerbating the patient’s condition. Therefore it is important for the optometrist to understand patients’ chief complaints with a thorough investigation of his anterior ocular health and a detailed history taking of his systemic, ocular health and environmental conditions that may suggest DE.
Since DE is multi-factorial, one must not just look into treating the disorder of the lacrimal system but patient’s lifestyle and environmental factors that may contribute to DES. Tear film instability or associated lid diseases may be improved with warm compresses using hot towels or microwavable eye masks. The practice of good hygiene is encouraged, especially for patients that apply makeup that may obstruct the orifices of the meibomian ducts, thus reducing the secretion of oil on the cornea surface. Advanced treatment using thermal pulsation system (LippiFLow®) have been offered in some countries though the efficacies and cost of treatment need to examined in more detail.
However, the use of topically administered lubricants is still regarded as first-line therapy for DE. The aim here is to stabilise the tear film, increase the tear volume and preserve the smooth refracting surface of the tear film. It also helps to improve lubricity of the ocular surface and hence reduce the friction of the eyelids on the cornea. All these, when put together, will create a more normal tear film environment for epithelial healing.
There are a wide range of over-the-counter artificial tear substitutes. They differ in their composition and hence vary in terms of viscosity and duration of action, presence and type of preservatives, osmolarity and PH. Some examples of lubricant polymers include hydroxypropyl methylcellulose (HPMC), carboxy methylcellulose (CMC), polyvinyl alcohol (PVA), carbopol polyvinyl pyrrolidone, dextran, hyaluronic acid (HA). These polymers may increase the viscous nature of the lubricants and may possibly facilitate adhesion to the mucus layer of the tears. HA is shown to benefit wound healing process; while hydroxypropyl Guar, when in contact with the pre-ocular tear film, forms cross linkages with borate to create a bio protective film. Naturally, the lesser the viscosity the formulation, the quicker the lacrimal outflow, reduced retention time and hence the more frequent the instillation. On the other hand, higher viscosity protects the ocular surface longer but causes visual disturbances; some may even precipitate as crystals on eyelids and lashes. Therefore the optometrist has to discuss and evaluate the pros and cons of the different types of OTC eye drops in managing and treating DES.
The Future for Contact Lens Wearers
While it is impossible to really summaries this area of study in one paragraph, it would be beneficial to highlight that manufacturers are tirelessly and relentlessly developing both contact lens and cleaning system that mimic the bio-compatibility of the ocular surface. While the past 10 years of developing silicone hydrogels have helped in improving the oxygen demand of the contact lens wearer, the fricto-mechanical relationship of the lens on the corneal surface remains to be studied in detail. The study of lid wiper epitheliopathy by Korb shows that evidence of damage to the lid wiper is related to the lack of lubrication of the ocular surface. A recent published data by Noel Brennan has proposed that of all lens attributes, it is the coefficient of friction (or lubricity) that is most highly correlated with lens comfort scores. Contact lens not just need to fulfil the oxygen demand of the eye but to also to possess the desired attributes of surface biocompatibility, wettability, tear film adherence and low friction properties. Lens cleaning systems (multi-purpose disinfecting solutions) have built in moisture locking lubricants to prevent water loss. Meanwhile, it is proposed that instilling a drop of lubricating eye drop prior to lens wear and after lens removal on symptomatic contact lens wearers may help prolong the comfort experienced by the wearers. Such initiative can alleviate patient’s intolerance to lens wear due to dryness. Management by way of advice and timely aftercare visits contact lens patients are important aspects of patient care. It is important to review the lens brand and the care system periodically as there will always be newer products that may benefit patients more. A status quo attitude in managing live long patients is not helpful as patients may silently leave our practice if nothing new is introduced to them.
Figure 2. Symptomatic SiHy patient with decreased tolerance to lens wear. Note the epithelial staining possibly associated to mechanical friction of lens on the ocular surface.
Figure 3. Same patient who was managed with change of solution to multipurpose with lubricating agent coupled with rubbing of lens as part of cleaning regime. She adopted the instillation of lubricant before wear and after lens removal. Note the staining was resolved and so was her symptoms of lens awareness and complaints of dryness.
Optometrists here are traditionally and culturally less apt in probing into the background of the patients’ health, and correspondingly patients are less forth right in disclosing them, especially so in the set-up of an eye exam room of an optical retail store. It is important that optometrist present and portray to the general public that primary eye care providers are fully capable of understanding ocular conditions and its systemic interactions, and handling them appropriately either by way of managing them at primary level or referring them for specialists’ opinion and treatment. This way of patient care would be beneficial to all as health care resource can be efficiently allocated while patient care is neither compromised nor delayed. Ultimately it is the desire of the optometrist to contribute more actively within the community and fit into the nation’s grand plan of first class health care for all.
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