Corneal sensitivity plays a critical role in maintaining ocular health. The cornea has the highest concentration of sensory and autonomic nerve fibers of any human tissue, which not only helps detect sensitivity but also provides essential nourishment to the corneal epithelium. Disruptions in tear film stability and ocular surface damage can lead to corneal epithelial barrier dysfunction, making the cornea more vulnerable to injury.
One common cause of tear film instability and dry eye disease is the long-term use of certain topical eye medications, especially those used to lower intraocular pressure in glaucoma patients. This can result in pain, visual impairment, and reduced corneal sensitivity, which may eventually lead to neurotrophic keratitis, a degenerative condition characterized by dysfunction of corneal innervation.
A recent study used a noncontact and handheld esthesiometer called the Corneal Esthesiometer Brill (CEB) to assess corneal sensitivity in patients with dry eye disease, glaucoma patients using IOP-lowering eye drops, and healthy individuals. The study found that both dry eye disease and glaucoma patients had significantly reduced corneal sensitivity compared to the control group. Additionally, dry eye disease patients reported more symptoms compared to both glaucoma patients and healthy individuals.
Corneal esthesiometry is not routinely performed in clinical practice due to the invasive and difficult-to-use nature of current devices. However, the CEB offers several advantages over existing esthesiometers. It does not require contact with the cornea, making it suitable for use in infectious corneal pathologies. The CEB also provides precise and reproducible results, with limited user bias.
The CEB has five levels of stimulation, with the first level being subthreshold and the subsequent levels corresponding to increasing levels of corneal sensitivity. Healthy corneas typically fall within levels 2 and 3, while patients with dry eye disease or glaucoma often have reduced sensitivity threshold at levels 4 and 5, indicating corneal hyposensitivity.
The noncontact esthesiometry provided by the CEB can serve as a valuable screening tool for detecting early stages of neurotrophic keratitis. Early identification of corneal nerve damage allows for timely intervention and treatment to prevent long-term damage to the ocular surface. For glaucoma patients, decreased sensitivity may be an indication to switch to preservative-free eye drops or consider alternative interventions. In cases of dry eye disease, decreased sensitivity may prompt the use of specific medications such as cenegermin (Oxervate) to manage neurotrophic keratitis.
In conclusion, the use of noncontact esthesiometry, particularly with the CEB, can aid in the early detection of neurotrophic keratitis and enable eye care professionals to implement targeted treatments to restore corneal function. It also provides an opportunity for ongoing evaluation of treatment effectiveness.
