In vivo confocal microscopy features and clinicohistological correlation of limbal nerve corpuscles

Aims To describe the in vivo confocal microscopy (IVCM) features of human limbal nerve corpuscles (LNCs) and correlate these with the histological features.Methods We examined 40 eyes of 29 healthy living subjects (17 female, 12 male; mean age=47.6) by IVCM. Four limbal quadrants were scanned through all epithelial layers and stroma to identify the LNCs and associated nerves. Ten fresh normal human corneoscleral discs from five deceased patients with a mean age of 67 years and 17 eye-bank corneoscleral rims with a mean age of 57.6 years were stained as whole mounts by the acetylcholinesterase (AChE) method to demonstrate LNCs and corneal nerves. Stained tissue was scanned in multiple layers with the NanoZoomer digital pathology microscope. The in vivo results were correlated to the histological findings.Results On IVCM, LNCs were identified in 65% of the eyes studied and were mainly (84%) located in the inferior or superior limbal regions. They appeared either as bright (hyper-reflective) round or oval single structures within the hyporeflective, relatively acellular fibrous core of the palisades or were clustered in groups, often located anterior to the palisades of Vogt. They measured 36 µm in largest diameter (range 20–56 µm). The in vivo features were consistent with the histology, which showed LNCs as strongly AChE positive round or oval structures.Conclusion The strong correlation with histology will enable use of IVCM to study LNCs in normal and disease conditions

Corneal Sensitivity and Dry Eye Symptoms in Patients with Keratoconus.

PURPOSE: 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; 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 Delta degrees C) and cold (KC: 1.28+/-0.27 vs. control: 0.98+/-0.25 Delta degrees 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). 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

Ex vivo confocal microscopy of human corneal nerves

International audienceAims: To evaluate the distribution, morphometry and the post-mortem changes of the central and peripheral human corneal nerves by ex-vivo laser-scanning confocal microscopy (EVCM). Methods: 24 eyes from 14 cadavers were retrieved at different time intervals after death and examined by EVCM. Five regions were examined in each eye namely central, superior, inferior, temporal and nasal. In each region, corneal nerve images were categorized according to their anatomical location in the cornea into sub-basal, stromal and limbal nerves. Five nerve parameters were measured; density, orientation, diameter, numbers and branching pattern. Results: Ex-vivo confocal scanning of a motionless eye allows high quality imaging and tracking of corneal and limbal nerves. Stromal nerves from the sub-Bowman's plexus perforate the Bowman's zone and terminate in blub like structures, from each of which a leash of sub-basal nerves arise. Following death, sub-basal nerve parameters showed significant changes. The density decreased from 9.23±4.48 to 0.45±0.07 mm/mm2; the diameter from 4.01±0.81 to 2.08±0.20 ìm; the numbers from 8.3 to 1.0 and branching pattern from 39.38% to 0% (p<0.05) from day one to day five post-mortem. Stromal and limbal nerves showed no significant changes in their density and diameter. Conclusions: This study establishes a direct link between sub-basal nerves and the sub-Bowmans nerves via distinct terminal bulbs. Limbal nerves are the thickest, are seen in all quadrants and can be traced to the corneal centre. The sub-basal nerve plexus rapidly degenerates after death but stromal and limbal nerves survive during the first five days after death

Clinical evaluation and characterisation of corneal vascularisation

Background/aims: To clinically characterise corneal neovascularisation (CVas) with a view to elaborate clinical presentations and to standardise descriptors for clinical evaluation and research.Methods: Corneas of 165 patients with CVas due to a variety of corneal pathologies were observed clinically with the slit lamp biomicroscope and photography at different time points over the course of their disease. Parameters assessed included location, depth, length, branching pattern, colour, lipid leakage, nature of blood flow and presence of haemorrhage. A clinical grading of CVas was applied.Results: CVas can arise from the limbus, conjunctiva and iris. CVas preferentially travels along planes created by corneal incisions, suture tracks and lamellar keratoplasty, both deep lamellar and endothelial keratoplasty. CVas also principally follows the depth of pathology. CVas can be classified into active young, active old, mature, partially regressed and regressed. Herpetic infection was the most common cause of lipid keratopathy. Acanthamoeba keratitis induced the least amount of vascularisation. A simple and efficient clinical grading system for ascertaining the severity of CVas was developed and validated.Conclusions :The various clinical characteristics of CVas described in this study can be used to standardise the nomenclature and description of CVas and clinically grade its severity. As modern, effective methods of treating CVas are being introduced, it is important that there is uniformity in the descriptors used to establish baseline values and evaluate outcomes of treatment. The parameters established in this study can help in this regard