Evaluation of Dry Eyes

Jason S. Rothman

Claudia U. Richter

A healthy tear film and ocular surface are necessary to help maintain the health and normal function of the eye. The prevalence of patients with dry eye syndrome is not precisely known, although epidemiologic data suggest it may be as high as 15% of patients over 65 years. Although there is no cure, early recognition and treatment can improve patient symptoms, can treat the underlying pathophysiology, and may delay progression. Dry eye syndrome may be due to systemic disease or medications, or may occur as part of the aging process. The primary physician’s role includes evaluating for possible underlying systemic disease(s), instructing patients on symptomatic measures, and referring to an ophthalmologist when appropriate.

PATHOPHYSIOLOGY AND CLINICAL PRESENTATION (1, 2, 3, 4 and 5)

Normal Tear Formation and Function

Normal tear volume ranges between 7 and 9 µL, although the thickness of the tear film on the eye surface varies. The tear film’s major functions are to maintain optical clarity, protect from infection, clear foreign matter and tissue debris, provide a
trophic environment for the underlying cornea and conjunctiva, and maintain surface comfort. The tear film has three major components—lipid, aqueous, and mucin. Previous research described the tear film as having three distinct layers comprised of each of these components. However, a new proposed structure is that of an aqueous/mucin gel, which increases its density closer to the ocular surface and is coated by an outermost lipid layer.

The outermost lipid layer is produced by the meibomian glands (holocrine-type glands) whose ducts open just anterior to the mucocutaneous junction (Marx line) on the upper and lower lid margins. This layer retards evaporation and counters gravitational forces on the aqueous layer. The aqueous component, secreted by the lacrimal and accessory lacrimal glands, accounts for the largest portion of the tear film. It contains the necessary growth factors, proteins, electrolytes, and antibodies to maintain the health of the eye’s surface. The mucin component is secreted by conjunctival and corneal goblet cells. Some mucins are bound to the surface, while soluble mucins are secreted into the tear film. The mucins decrease surface tension and create a hydrophilic ocular surface. A normal blink rate and eyelid closure are critical components to distribute and maintain the tear film.

Pathophysiology

Dry eye syndrome is characterized by a reduction of tear volume, tear hyperosmolarity, and inflammation of the tear film and ocular surface. Mild dry eye is common in the elderly as tear secretion is reduced with age (secondary to hormonal and neural changes). Medications, such as diuretics and drugs with anticholinergic properties (e.g., antihistamines, tricyclic antidepressants, bladder relaxants, and psychotropics), will reduce tear secretion. Risk for dry eye symptoms is particularly high when three or more drugs with known drying side effects are used concurrently. Prolonged visual efforts from reading or computer use may reduce blink rate and lead to dry eye due to increased tear film evaporation.

Blepharitis (infectious, inflammatory, or allergic) may alter the meibomian gland oil production and composition, causing an evaporative dry eye, and/or directly irritate the ocular surface. Rosacea and staphylococcal blepharitis are common etiologies. Lagophthalmos, incomplete blink, and eyelid malposition often will cause or exacerbate dry eye syndrome. Patients with an inadequate seal around a continuous positive airway pressure (CPAP) mask and those with nocturnal lagophthalmos will often present with severe dry eye symptoms in the morning.

Systemic pathology may result in dry eyes. Sjögren syndrome is a chronic disorder characterized by severe dry eyes and mouth. This can be either primary (patients without an associated autoimmune disease) or secondary (patients with an associated autoimmune disease). The most common condition associated with secondary Sjögren syndrome is rheumatoid arthritis. Other conditions include systemic lupus erythematosus, autoimmune hemolytic anemia, polyarteritis nodosa, and Raynaud phenomenon. In both primary and secondary Sjögren syndrome, the lacrimal and salivary glands are infiltrated with lymphocytes, causing a reduction in tear and saliva secretion. Ocular cicatricial pemphigoid and Stevens-Johnson syndrome can cause severe conjunctival inflammation, scarring, goblet cell destruction, and dry eye. Less common etiologies include vitamin A deficiency, graft versus host disease, Riley-Day syndrome, and anhidrotic ectodermal dysplasia.

Clinical Presentation

Patients with dry eyes typically complain of irritation, grittiness, burning, difficulty in moving or opening the eyelids, and/or a foreign-body sensation. Symptoms can vary from day to day or change during the day. Patients may also notice vision fluctuation, commonly while reading or using the computer. When ocular irritation stimulates reflex tearing, dry eye patients may present paradoxically with tearing. Although not exclusive to dry eyes, eyes may also be red. Rarely, dry eyes may be so severe as to cause corneal ulceration.

DIFFERENTIAL DIAGNOSIS (2,4,6)

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