Abstract
BackgroundThe inter-visit variation of measuring bulbar conjunctival microvasculature and microcirculation needs to be considered when the results from multiple visits are interpreted. This study examined the inter-visit variability of measuring conjunctival microvasculature and microcirculation in habitual contact lens (HCL) wearers and non-contact lens (NCL) wearers.MethodsTwenty-eight subjects were recruited including 13 HCL wearers (10 females and 3 males; mean age ± standard deviation, 25.8 ± 4.6 years) who had worn contact lenses on a daily basis for at least 3 years and 15 NCL wearers (10 females and 5 males, age 25.5 ± 4.0 years) were recruited. The temporal bulbar conjunctiva was imaged using a functional slit-lamp bio-microscope (FSLB) imaging system. FSLB imaging was performed in the morning when the HCL wearers did not wear their lenses. The measurements included conjunctival vessel diameter, vessel density, blood flow velocity and flow volume. In addition, conjunctival microvasculature was analyzed using monofractal (Dbox, representing vessel density) and multifractal (D0 representing vessel complexity) analyses. The repeated measurement was conducted at least one week after the first visit and both eyes of each participant were imaged. The coefficient of variation (CV) was calculated as the standard deviation of the differences between test and re-test then divided by the mean of the measurements. The intra-class correlation coefficient (ICC) was also calculated.ResultsNo significant differences of all vascular measurements in both the right and left eyes were found between two groups (P > 0.05). Between two measurements on two different visits, the CV was from 2.4% (vessel density D0) to 63.5% (blood flow volume Q) in HCL wearers and from 3.4% (D0) to 40.6% (blood flow volume) in NCL wearers. The ICC was from 0.60 (vessel diameter) to 0.81 (axial blood flow velocity VA) in HCL wearers and from 0.44 (Q) to 0.68 (cross-sectional blood flow velocity VS) in NCL wearers.ConclusionsThe measurement variability of the vessel density of the bulbar conjunctiva appeared to have the smallest inter-visit variation. The measurement variability of the vasculature and circulation in HCL wearers were similar to that in NCL wearers.
Highlights
The inter-visit variation of measuring bulbar conjunctival microvasculature and microcirculation needs to be considered when the results from multiple visits are interpreted
Contact lens wear induces some level of low oxygen supply, lenses with high oxygen transmission materials [1,2,3] may already eliminate the issue with daily wear of contact lenses
When the eyelid is open, oxygen from the ambient air diffuses into the bulbar conjunctival microvasculature, which highly oxygenates all exposed micro-vessels within 10 s [4]
Summary
The inter-visit variation of measuring bulbar conjunctival microvasculature and microcirculation needs to be considered when the results from multiple visits are interpreted. This study examined the inter-visit variability of measuring conjunctival microvasculature and microcirculation in habitual contact lens (HCL) wearers and non-contact lens (NCL) wearers. In neophytes who have never had experience with contact lenses, contact lens wear induced a 30% increase of bulbar conjunctival blood flow velocity after 6 h of lens wear [5]. Bulbar conjunctival blood flow velocity in habitual lens wearers was about 22% higher than normal controls when they wore their lenses [6]. As noted from our previous study, these habitual lens wearers did not notice that their bulbar conjunctivas appeared to be slightly red. These subtle changes may indicate an ongoing response to contact lens wear. There is a knowledge gap in the inter-visit measurement variation, which is essential for calculating sample sizes and study designs of clinical research on contact lenses
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