dry eye dx and tx
Protecting Dry Eyes From Harm
BY WILLIAM TOWNSEND, OD, FAAO
The surface of a dry eye is a fragile thing. Alterations in tear film osmolarity, electrolyte composition, surface mucins, microvilli and blink rate render the ocular surface susceptible to insult.
In dry eye syndrome the altered composition of ocular surface cells often demonstrates the extent to which normal cellular architecture has been affected. Marube and Rivas (2003) obtained conjunctival biopsies from Sjögren's Syndrome patients and found progressive stratification, hyperplasia, hypertrophy and cellular flattening of conjunctival cells; they also found a reduction in goblet cell density and mucous layer thickness. These cellular changes render the surface more susceptible to loss of surface-adherent mucins and rapid tear film breakup, ultimately leaving underlying conjunctival and corneal surface cells unprotected.
Medications may exacerbate the breakdown of surface tissue. Ousler et al (2007) showed that systemic loratadine was associated with a 34 percent reduction in tear volume, 35 percent reduction in tear flow and 22 percent increase in global fluorescein staining. In Ousler et al (2004), systemic loratadine caused a 107 percent increase in keratitis, 133 percent increase in conjunctival staining, and a decrease of 1.38 seconds (34 percent) in TBUT. Cetirizine hydrochloride yielded a 60 percent increase in keratitis, 50 percent increase in conjunctival staining and 20 percent decrease in TBUT versus baseline.
Watch for Preservatives
In prescribing products for dry eye patients, consider the potential effects a preparation may have on ocular surface tissue. The most common preservative in ophthalmic preparations is benzalkonium chloride (BAK). Göbbels and Spitznas (1992) found use of BAK-preserved artificial tears increased corneal permeability more than no treatment at all. In other words, dry eye patients are better off using no artificial tears than BAK-preserved options.
A study by De Saint et al (1999) showed that conjunctival epithelial cells exposed to BAK in concentrations from 0.1% to 0.0001% exhibited dose-dependent growth arrest and cell death.
But some defend the use of BAK for ophthalmic solutions. Abelson and Fink (2002) found that epithelial cells exposed to commercially available concentrations of BAK did not significantly differ from those exposed to preservative-free eye drops.
Adverse effects of medications can extend beyond simple toxicity; Ozdal et al (2002) showed that many ocular preparations are chemotactic for neutrophils. Several studies have established the undesirable effect of chronic medications such as glaucoma therapy. Long-term topical therapy can increase inflammatory mediators and cause changes in connective tissue. Guenoun et al (2005) evaluated three topical prostaglandin analogs for cytotoxic and apoptotic effects and concluded that inherent toxicity of the analogs was less important than the deleterious effects of preservatives, specifically BAK.
Prescribing for Dry Eyes
We must carefully weigh the benefits of a medication against the potential complications or damage from chronic use when prescribing for dry eye patients. Following are some guidelines:
• When possible, steer dry eye patients away from artificial tear products preserved with BAK.
• Review systemic medications that may exacerbate ocular dryness.
• Consider the potential effects of BAK-preserved medications for persistent conditions such as glaucoma, allergy, etc.
• When BAK-preserved products are indicated, select the one with the lowest dosing frequency.
• When prescribing a lifetime drug such as glaucoma therapy, consider a medication that is non-preserved or preserved with a tissue-friendly molecule. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #146.
Dr. Townsend practices in Canyon, Texas and is an adjunct faculty member at UHCO. E-mail him at firstname.lastname@example.org.