Corneal sensation is supplied by the ophthalmic division of the fifth (trigeminal) cranial nerve. Corneal esthesiometry is typically used clinically to evaluate for neurotrophic keratopathy.
In the clinical setting, an evaluation of corneal sensation is most commonly achieved with a cotton-tipped applicator. This is performed without topical anesthesia and should be done before IOP is checked. A wisp of cotton from the cotton-tipped applicator is used to compare sensation in each eye. Approaching the patient from the side and testing all 4 quadrants has the advantage of eliminating false-positive responses, which result when the patient sees the cotton-tipped applicator approaching the eye. The sensation in each location is recorded as normal, reduced, or absent.
Various quantitative methods exist, but they are typically reserved for research or complex cases. The most common quantitative method is use of the handheld (Cochet-Bonnet) esthesiometer; this is discussed in the following section. Other methods include the noncontact air-puff technique, chemical stimulation using capsaicin, and thermal stimulation with a carbon dioxide laser.
The handheld (Cochet-Bonnet) esthesiometer is a device that contains a thin, retractable nylon monofilament. Adjusting the length of the monofilament changes the pressure applied by the device. The maximum length is 60 mm, and the minimum length is 5 mm; as the length decreases, the pressure increases from a minimum of 11 mm/gm to a maximum of 200 mm/gm.
Steps for using the handheld esthesiometer are as follows:
Extend the filament to the full length of 60 mm.
Retract the filament in 5-mm increments until the patient can feel its contact.
Record the length. (Note: The shorter the length, the lower the sensation.)
Repeat steps 1–3 in the fellow cornea.
Repeat steps 1–4 in each quadrant: superior, temporal, inferior, and nasal.
Clean the filament and retract it into the device.
Greiner MA, Faulkner WJ, Vislisel JM, Varley GA, Goins KM. Corneal diagnostic techniques. In: Mannis MJ, Holland EJ, eds. Cornea. Vol. 1. 4th ed. Philadelphia: Elsevier; 2017:116–122.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.