This article was originally published in a sponsored newsletter.
Dry eye disease (DED) and neurotrophic keratitis (NK) are distinct yet interconnected ocular conditions that affect the health and functionality of the corneal surface. While they share overlapping features, their underlying mechanisms and clinical presentations differ significantly, making an accurate diagnosis essential for effective management.
Dry Eye Disease: A Chronic Condition of Imbalance
DED is characterized by a loss of homeostasis on the ocular surface. This imbalance arises from factors such as inflammation, tear film instability, hyperosmolarity and neurosensory abnormalities. Perpetuated by prolonged stress and unresolved inflammation, these elements create a vicious cycle that leads to chronic DED.
One unique aspect of DED is its impact on neural signaling between the ocular surface and the central nervous system. Over time, this disruption can lead to reduced corneal nerve density and sets the stage for the development of NK in susceptible patients.
Neurotrophic Keratitis: A Degenerative Disease
NK is a degenerative corneal disease that results from impaired corneal sensory innervation, primarily involving the trigeminal nerve. This nerve is critical for maintaining corneal health by regulating blinking, tear production and the secretion of trophic factors that support epithelial regeneration. When corneal nerve function is compromised, as in NK, these processes falter, leading to corneal staining, persistent epithelial defects and, in severe cases, corneal ulcers.
Unlike DED, NK is often marked by reduced corneal sensitivity. Patients may inadvertently create diagnostic challenges by not reporting symptoms proportionally to the extent of corneal damage. NK is often associated with specific risk factors, including diabetes, chronic use of topical medications, neurosurgical procedures, chemical burns or a history of herpes or zoster infections.
Diagnosing DED and NK
Given the overlapping pathologies of DED and NK, some patients may present with both conditions simultaneously. Differentiating them requires a thorough assessment of the signs and symptoms. In typical cases of DED with severe corneal staining, patients often report significant discomfort. In contrast, an eye affected by both DED and NK may exhibit intense corneal staining but present with disproportionately mild symptoms due to reduced corneal sensitivity.
DED is typically a bilateral condition. However, if a patient displays asymmetric corneal staining, it is prudent to suspect NK in the eye with more severe staining. To confirm this diagnosis, conduct a corneal sensation test with a Cochet-Bonnet aesthesiometer to precisely measure corneal sensitivity, or with dental floss, gauze or a modified cotton swab for a simpler touch test. In a healthy eye, the touch test typically elicits a flinching response or causes the patient to move away from the slit lamp. The absence of such responses, or a lack of reported sensation, indicates reduced corneal sensitivity and the presence of NK.
Once diagnosed, DED and NK require immediate management to prevent disease progression because advanced stages become increasingly difficult to treat.
