Corneal Sensitivity and Dry Eye Symptoms in Patients with Keratoconus

PurposeTo investigate corneal sensitivity to selective mechanical, chemical, and thermal stimulation and to evaluate their relation to dry eye symptoms in patients with keratoconus.MethodsCorneal 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.ResultsKC 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; p0.05). 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 (p0.05), 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).ConclusionsCorneal 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.研究目的 探究圆锥角膜（keratoconus）患者角膜对选择性机械、化学及温度刺激的敏感性，并分析其与干眼症状的关联。 研究方法 本研究纳入19例圆锥角膜患者（圆锥角膜组，KC组）与20名年龄匹配的健康受试者（对照组），采用气体触觉测量仪（gas esthesiometer）检测受试者角膜对机械、化学及温度刺激的阈值；通过施墨I试验（Schirmer I test）与无创泪膜破裂时间（non-invasive tear film breakup time, NI-BUT）评估泪膜动力学特征；所有受试者均接受旋转Scheimpflug相机检查，以评估圆锥角膜的严重程度。 研究结果 与对照组相比，圆锥角膜组患者的泪液分泌量显著降低，眼表疾病指数（ocular surface disease index, OSDI）评分显著升高（分别为5.3±2.2 vs. 13.2±2.0 mm与26.8±15.8 vs. 8.1±2.3；P<0.05）。圆锥角膜组患者对选择性机械刺激（圆锥角膜组：139.2±25.8 ml/min vs. 对照组：109.1±24.0 ml/min）、化学刺激（圆锥角膜组：39.4±3.9 %CO₂ vs. 对照组：35.2±1.9 %CO₂）、热刺激（圆锥角膜组：0.91±0.32 Δ°C vs. 对照组：0.54±0.26 Δ°C）及冷刺激（圆锥角膜组：1.28±0.27 Δ°C vs. 对照组：0.98±0.25 Δ°C）的平均阈值均显著高于对照组（P<0.05）。而对照组中，机械刺激阈值（r=0.52，P=0.02）、化学刺激阈值（r=0.47，P=0.04）、热刺激阈值（r=0.26，P=0.04）及冷刺激阈值（r=0.40，P=0.03）均随年龄增长而升高。在圆锥角膜组中，角膜厚度、泪液流量、NI-BUT及OSDI评分与机械、化学、热或冷刺激阈值均无显著相关性（所有变量P>0.05）。 研究结论 圆锥角膜患者角膜对各类刺激的敏感性均有所降低，且该降低不受年龄与疾病严重程度的影响。角膜神经传入的感觉信号减少，可能是此类患者出现不适症状的诱因之一，也可能导致泪膜动力学异常。