Dry Eye Syndrome, Preservatives, and Glaucoma

posted in: Eye Conditions

The interface of legal aspects of dry eye syndrome and glaucoma is of interest to ophthalmologists and attorneys.  This article summarizes some of the major clinical points of dry eyes, preservatives, and glaucoma.

Glaucoma is a serious, chronic condition that is generally characterized by elevated eye pressure resulting in degeneration of the optic nerve.  The incidence of glaucoma and dry eyes rises with increasing age.  Glaucoma and dry eyes can affect each other through various mechanisms.  Studies indicate that about 60% of patients with glaucoma also have some form of dry eye disease.  Both of these conditions can cause visual loss and thus the quality of life.

Glaucoma is usually responsive to medical therapy in the form of eyedrops.  Physicians who treat patients with glaucoma need to consider the risks and benefits of all treatments for their patients, including the use of medications for treating glaucoma.  Medications for glaucoma may cause red eyes, eye irritation, and a foreign body sensation that is often described as a sandy feeling.

In addition to pollutants and allergens, the active ingredient and the preservative in glaucoma medications may exacerbate eye problems that are also common to dry eyes.  Often, it is difficult to isolate the effects of long-term medication for glaucoma with symptoms from dry eye syndrome.

Preservatives in glaucoma eyedrops may result in:

1)     Ocular discomfort, such as burning, foreign body sensation and stinging.

2)     Instability of the tear film.

3)     Impairment of the surface of the cornea, such as punctate erosions.

4)     Limitation of compliance from symptoms of discomfort.

Preservatives used in medications are one important consideration.  One of the earliest preservatives in glaucoma medications was benzalkonium chloride (BAK).  First used in contact lens solutions, BAK has gained popularity in glaucoma medications because of predicate FDA approval for contact lens solutions.  BAK is a very effective preservative, minimizing bacterial and fungal growth in glaucoma medications.  Other preservatives used in glaucoma medications include Purite (Allergan), SofZia (Alcon).  Oxidizing preservatives like Purite and ZofZia have less of an effect on cells of the surface of the eye than does BAK.  Curiously, for unknown reasons the active ingredient in glaucoma medications appear to have a protective effect on the surface of the eye.

Because of potentially adverse reactions of the eye to preservatives, some companies have manufactured glaucoma eyedrops without preservatives.  Among these companies is Aton Pharma, which manufactures a preservative-free form of timolol maleate known as Ocudose.  Tafluprost is a prostaglandin analogue that is free of BAK.  It is also important to remember that the primary cause of worsening of dry eye syndrome in patients who are treated for glaucoma is the preservative in eyedrops.

The mechanism of impairment from glaucoma eyedrops is related to direct injury to the surface and also inducement of the superficial cells, also known as the epithelium, to create inflammatory markers.  For reasons that are yet unknown, even very low concentrations of preservatives may have an adverse effect on the surface of the eye.

Dryness of the eye may be assessed through various means.  Some of the most common methods for assessing dry eye include:

1)     Tear breakup: 7 to 10 seconds is a normal measure.

2)     Schirmer tear testing: Limited in value because it is not highly specific or sensitive.

3)     Corneal examination: punctate erosions of the surface of the eye.

4)     Lissamine Green staining of the conjunctiva: Uptake of dye indicates epithelial dysfunction related to dryness.

5)     Lid margin disease.  The presence of froth along the lid margins, neovascularization of the lid margins, or excessive opaque oil secretion from meibomian glands along the lid margin is often associated with dry eye syndrome.

Often, patients with severe dry eyes do not experience symptoms.  This paradoxical phenomenon may be due to denervation of the ocular surface from inflammation changes due to dry eyes.  Researchers have also considered tear osmolarity and corneal permeability as markers for dry eyes.

Dry eyes may be treated with artificial tears that have either no preservatives or mild preservatives.  The choice of artificial tears depends on the composition, viscosity, and mechanism of action that is selected by the doctor.  Lacrisert is a tear pellet that melts after it is placed in the cup behind the lower eyelid.  Restasis eyedrops may improve tear production, but it may take months before the effects of Restasis become apparent.  Dry eyes associated with significant lid margin disease may be treated with warm soaks and lid scrubs.

Dry eyes exacerbated by medications needs to be considered when treating patients for glaucoma.  When patients complain of chronic eye pain, chronic irritation, or variable vision throughout the day, clinicians need to consider the possibility of preservatives as a cause.  Examination features that include tear breakup time.  Lissamine green staining, or punctate erosions in the cornea, are key findings that clue the clinician to dry eye related problems.  Some studies indicate that almost 50% of patients experience symptoms related to dry eye disease.  Managing glaucoma and possible effects from preservatives in patients with underlying dry eyes is a challenge that needs to be considered in patients with long-term issues.

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