Clinical findings of corneal hyperplasia and irregularity, scattered small facets of dried epithelium, decreased nerve density as assessed by in vivo confocal microscopy (IVCM), and decreased corneal sensation.

Clinical findings of corneal epithelial defect with smooth and rolled edges, decreased nerve density as assessed by in vivo confocal microscopy (IVCM), and decreased corneal sensation.

Symptoms of dry eye disease for at least 3 months, supported by clinical finding of decreased tear film break-up time or ocular surface staining. Normal corneal sensation.

Absence of any ocular symptoms, absence of surface findings (including corneal or conjunctival staining, corneal scar or surgical wound), and normal corneal sensation.

Quantitative Sensory Test (Medoc Ltd, Israel), QST is a non-invasive neurophysiological method that refers to a group of procedures that assess the perceptual responses to systematically applied and quantifiable sensory stimuli (modalities including heat, cold and vibration) for the purpose of characterizing somatosensory function or dysfunction. For this test, subjects will be seated comfortably on a chair in a quiet room, or laying supine in a horizontal examination chair, with ambient temperature of 24-25◦ C. Medial upper eyelid; just below the supraorbital notch, nasolacrimal sac area; 4-5 mm medial to nasal cantus, and non-dominant forearm will be used as test sites. Patients will be instructed in detail of the nature of the test and the need to react attentively and promptly to change in temperatures.

Cold and heat sensation thresholds will be evaluated by placing a 16 mm x 16 mm probe over the skin on the site to be tested, and an average of 3 reading while be taken for each stimuli. Participants will receive successive ramps of gradually decreasing or increasing temperature, starting from a resting neutral temperature of 32°C. Participants will be instructed to press a response button when a thermal sensation (either cold or warm) is perceived.

Vibration sensation threshold will be evaluated by placing a 16 mm x 16 mm probe over the skin on the site to be tested, and an average of 3 reading while be taken. Participants will receive successive ramps of gradually decreasing or increasing vibration, starting from. Participants will be instructed to press a response button when a mechanical sensation is perceived.

Cold pain threshold (CPT) and heat pain threshold (HPT) will be measured by asking participants to press a response button when they first feel a pain or discomfort from probe on QST testing

Vibration pain threshold (VPT) will be measured by asking participants to press a response button when they first feel a pain or discomfort from vibration probe on QST testing

In vivo confocal microscopy (IVCM) imaging will be performed to observe for any morphological nerve changes; such as decreased nerve density, nerve tortuosity presence of microneuromas.