Dry Eye Dx and Tx

One Eye Dry? Managing Unilateral Dry Eye, Part 2

By William Townsend, OD, FAAO

When a patient presents with unilateral or asymmetric dry eye, you need to consider a broad spectrum of potential causes. Neurological disease may trigger unilateral dry eye from seemingly unrelated conditions. Crane and Basha (2008) reported the case of a 48-year-old female who presented with right upper lid ptosis and severe unilateral dryness in her right eye. The case history revealed that the patient had previously suffered fracture of cervical vertebrae C3-C4, near the site where the sympathetic nerves that innervate Mueller's muscle originate. The ptosis resolved with administration of phenylephrine 2.5%, confirming a diagnosis of ptosis secondary to sympathetic denervation of Mueller's muscle and presumed aqueous tear deficiency from denervation of the lacrimal gland. This case demonstrates the value of collecting a thorough medical history including past injuries of the head and neck.

Decreased Corneal Sensation

Diminished corneal sensation can result from a wide variety of conditions and is a common cause of unilateral dry eye (Benitez-Del-Castillo et al, 2007; Toker and Asfuroglu, 2010). Reduced sensation can be confirmed with aesthesiometry. In clinical practice, we need an effective tool for screening corneal sensitivity such as by touching the apex of the cornea with a cotton wisp or with non-flavored dental floss (Margolis, 2012).

Neurotrophic keratopathy (NK), a degenerative corneal disease involving impaired corneal sensation, is an important cause of unilateral dry eye. Many conditions can lead to NK, but the basic pathophysiology is trigeminal nerve (V) denervation, which results in surface alterations and dry eye.

The Mackie classification delineates NK into three stages. Stage 1 NK includes corneal irregularity, dry spots, punctate keratopathy, superficial vascularization, stromal scarring, and epithelial hyperplasia (Lambiase et al, 1999). Grade 2 NK presents with epithelial deficit, usually in the superior cornea surrounded by an area of loose epithelium; there may also be stromal edema. Grade 3 disease is characterized by corneal ulceration, stromal melting, and perforation. Several studies have shown the importance of innervation in preserving the health of epithelial cells. Araki et al (1994) reported that denervation of rabbit corneas led to alterations in the epithelial surface and adherence between cells. Ultimately, spontaneous epithelial breakdown was widespread; 83 percent of the corneas showed persistent epithelial defects.

Managing a Denervated Cornea

Management of a denervated cornea and accompanying dry eye can be very challenging. Some of the recommended therapies for milder cases include non-preserved artificial tears. For more severe presentations, lateral tarsorrhaphy and amniotic membrane transplantation may be indicated (Lambiase et al, 1999). Lambiase et al (1998) reported good results in treating refractory neurotrophic ulcers with nerve growth factor (NGF). Reynolds and Kabat (2006) described the case of a 46-year old female who had NK secondary to herpes simplex keratitis. She was previously treated with bandage contact lenses, topical antibiotic, and artificial tears with marginal success. Four weeks after adding b.i.d. Restasis (Allergan), the patient was able to discontinue the bandage lenses and antibiotic. CLS

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