Human ocular surface microcirculation quantified by in vivo computer assisted video microscopy and diffuse reflectance spectroscopy.

Non-invasive imaging techniques are increasingly used to objectively quantify anterior segment structures of the eye. In this study, we apply the novel oxygen delivery index (ODIN) concept that, quantifies microvascular capacity for oxygen delivery, to the ocular surface in healthy humans. The purpose of the study was to test the applicability of the technologies used for data acquisition from the human ocular surface. We also validated whether the ODIN concept has sufficient sensitivity to detect and differentiate between microvascular structure and function in limbal and bulbar conjunctiva. Multiple ocular surface measurements using computer-assisted video microscopy (field of view: 1.6 mm × 0.9 mm) and diffuse reflectance spectroscopy (measuring volume: ∼0.1 mm3) were obtained from limbal and bulbar conjunctiva in 20 healthy volunteers. Three parameters were extracted during analyses: Functional capillary density, capillary flow velocity, and microvascular oxygen saturation. Functional capillary density was higher at limbus than in bulbar conjunctiva (11.2 ± 1.8 c/mm versus 5.2 ± 1.2 c/mm, p < 0.01), and microvascular oxygen saturation was lower at limbus (77 ± 8%) as compared to bulbar conjunctiva (89 ± 6%), p < 0.01. More than 80% of scored capillaries had continuous blood flow and no difference was seen between the recording sites (p = 0.68). In conclusion, the ODIN concept is applicable for the assessment of human ocular surface microvascular function and has sufficient sensitivity to detect increased capillary density and oxygen extraction at limbus as compared with bulbar conjunctiva.

Microvascular remodeling following skin injury.

OBJECTIVE: The aim of this study was to describe possible remodeling (i.e., dilatation and elongation) of papillary capillaries induced by increased oxygen demand for the repair process following a skin wound. METHODS: Computer-assisted video microscopy was used to examine 10 healthy volunteers before (baseline) and after (≈1 h and ≈24 h) an incision (5 mm long and 1 mm deep) on the forearm, 0-1 mm and 30 mm (control site) from the incision. We defined categories from 0 (low) to 3 (high) to grade dilatation and elongation of the nutritive papillary capillaries, as well as the visibility of the superficial vascular plexus. Approximately 10 000 capillaries from 200 films were scored. RESULTS: The nutritive papillary capillaries were dilated and elongated (p < 0.01) after ≈24 h; that is, elongation (score 1.9 ± 0.9) vs baseline (score 0.9 ± 0.6), p < 0.01 and dilatation (score 2.2 ± 0.7) vs baseline (score 0.3 ± 0.3), p < 0.01. Superficial plexus visibility increased (p < 0.01) after ≈1 h (score 2.0 ± 0.7) and ≈24 h (score 2.7 ± 0.3) vs baseline (score 0.8 ± 0.4). CONCLUSION: The superficial vascular skin plexus showed enhanced visibility already ≈1 h after the skin trauma. Morphological remodeling in the nutritive papillary capillaries-dilatation and elongation after ≈24 h-facilitate increased O2  supply.

Skin trauma rapidly induces thermoregulatory plexus hyperemia, while an increased nutritive papillary capillary function can be detected after 24 h.

OBJECTIVE: Clinical assessments and laser Doppler perfusion measurements (LDPM) of skin microcirculation have limited value, as they fail to capture events regulated by local metabolic needs at a papillary capillary level. This study aimed to examine the ability of computer-assisted video microscopy (CAVM) and diffuse reflectance spectroscopy (DRS) to assess skin nutritive perfusion-compared to LDPM. METHODS: Healthy volunteers (n = 10) were examined after (≈1 and ≈24 h) an incision (5 × 1 mm) on the forearm, at 0.1 mm (only with CAVM), 2-3 mm, and 30 mm from the trauma. RESULTS: No changes were detected by CAVM after ≈1 h. After ≈24 h, 0-1 mm from the trauma, both CAVM parameters were increased: functional capillary density (capillary crossings/mm, 11.8 ± 1.4 vs. 7.3 ± 1.2, p < .01) and capillary flow velocities (CFV, %capillaries with brisk flow, 10 ± 6.8 vs. 1 ± 1, p < .01). At a distance of 2-3 mm, only CFV was increased (6.2 ± 6.1 vs. 1 ± 1, p < .05). DRS and LDPM measurements increased 2-3 mm from the trauma line in relation to baseline after both ≈1 and ≈24 h, that is, with DRS (%microvascular oxygen saturation): 45.8 ± 7.4% (baseline), 70.0 ± 12.5% (≈1 h), and 73.1 ± 10.4% (≈24 h), p < .01 and with LDPM (a.u.): 7.2 ± 2.5 (baseline), 28.3 ± 18.7 (≈1 h), and 45.9 ± 16.3 (≈24 h), p < .01. CONCLUSIONS: ≈24 h after skin trauma, an increased function of the nutritive papillary capillaries can be detected by CAVM.

Quantification of ocular surface microcirculation by computer assisted video microscopy and diffuse reflectance spectroscopy.

In piglets we tested the applicability of digital video microscopy and diffuse reflectance spectroscopy for non-invasive assessments of limbal and bulbar conjunctival microcirculation. A priori we postulated that the metabolic rate is higher in limbal as compared to bulbar conjunctiva, and that this difference is reflected in microvascular structure or function between the two locations. Two study sites, Oslo University Hospital (OUH), Norway and Cleveland Clinic (CC), USA, used the same video microscopy and spectroscopy techniques to record limbal and bulbar microcirculation in sleeping piglets. Recordings were analyzed with custom-made software to quantify functional capillary density, capillary flow velocity and microvascular oxygen saturation in measuring volumes of approximately 0.1 mm3. The functional capillary density was higher in limbus than in bulbar conjunctiva at both study sites (OUH: 18.1 ± 2.9 versus 12.2 ± 2.9 crossings per mm line, p < 0.01; CC: 11.3 ± 3.0 versus 7.1 ± 2.8 crossings per mm line, p < 0.01). Median categorial capillary blood flow velocity was higher in bulbar as compared with limbal recordings (CC: 3 (1-3) versus 1 (0-3), p < 0.01). Conjunctival microvascular oxygen saturation was 88 ± 5.9% in OUH versus 94 ± 7.5% in CC piglets. Non-invasive digital video microscopy and diffuse reflectance spectroscopy can be used to obtain data from conjunctival microcirculation in piglets. Limbal conjunctival microcirculation has a larger capacity for oxygen delivery as compared with bulbar conjunctiva.