Corneal Sensitivity and Dry Eye Symptoms in Patients with Keratoconus.
OBJECTIVE
To investigate corneal sensitivity to selective mechanical, chemical, and thermal stimulation and to evaluate their relation to dry eye symptoms in patients with keratoconus.


METHODS
Corneal sensitivity to mechanical, chemical, and thermal thresholds were determined using a gas esthesiometer in 19 patients with keratoconus (KC group) and in 20 age-matched healthy subjects (control group). Tear film dynamics was assessed by Schirmer I test and by the non-invasive tear film breakup time (NI-BUT). All eyes were examined with a rotating Scheimpflug camera to assess keratoconus severity.


RESULTS
KC patients had significatly decreased tear secretion and significantly higher ocular surface disease index (OSDI) scores compared to controls (5.3±2.2 vs. 13.2±2.0 mm and 26.8±15.8 vs. 8.1±2.3; p<0.001). There was no significant difference in NI-BUT between the two groups (KC: 9.8±4.8 vs. control: 10.7±3.8; p>0.05). The mean threshold for selective mechanical (KC: 139.2±25.8 vs. control: 109.1±24.0 ml/min), chemical (KC: 39.4±3.9 vs. control: 35.2±1.9%CO2), heat (KC: 0.91±0.32 vs. control: 0.54±0.26 Δ°C) and cold (KC: 1.28±0.27 vs. control: 0.98±0.25 Δ°C) stimulation in the KC patients were significantly higher than in the control subjects (p<0.001, for all parameters). No correlation was found between age and mechanical, chemical, heat or cold thresholds in the patients with KC (p>0.05), whereas in the control subjects both mechanical (r = 0.52, p = 0.02), chemical (r = 0.47, p = 0.04), heat (r = 0.26, p = 0.04) and cold threshold (r = 0.40, p = 0.03) increased with age. In the KC group, neither corneal thickness nor tear flow, NI-BUT or OSDI correlated significantly with mechanical, chemical, heat or cold thresholds (p>0.05 for all variables).


CONCLUSIONS
Corneal sensitivity to different types of stimuli is decreased in patients with keratoconus independently of age and disease severity. The reduction of the sensory input from corneal nerves may contribute to the onset of unpleasant sensations in these patients and might lead to the impaired tear film dynamics.
Semmelweis University, Department of Ophthalmology, Budapest, Hungary.
Lóránt
L
Dienes
Semmelweis University, Department of Ophthalmology, Budapest, Hungary.
Huba J
HJ
Kiss
Semmelweis University, Department of Ophthalmology, Budapest, Hungary.
Kristóf
K
Perényi
Semmelweis University, Department of Ophthalmology, Budapest, Hungary.
Zoltán Z
ZZ
Nagy
Instituto de Neurociencias, Universidad Miguel Hernandez-CSIC, San Juan de Alicante, Spain.
M Carmen
MC
Acosta
Instituto de Neurociencias, Universidad Miguel Hernandez-CSIC, San Juan de Alicante, Spain.
Juana
J
Gallar
Semmelweis University, Department of Ophthalmology, Budapest, Hungary.
Illés
I
Kovács
D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D003315:Cornea / Q000503:physiopathology*; D015352:Dry Eye Syndromes / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D013666:Tears / Q000378:metabolism; D013697:Thermosensing; D014110:Touch; D055815:Young Adult