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. 1999 Jan;83(1):92–97. doi: 10.1136/bjo.83.1.92

Reflective meniscometry: a non-invasive method to measure tear meniscus curvature

N Yokoi 1, A Bron 1, J Tiffany 1, N Brown 1, J Hsuan 1, C Fowler 1
PMCID: PMC1722770  PMID: 10209444

Abstract

AIMS—To devise a method to measure tear meniscus curvature by a non-invasive specular technique.
METHODS—A photographic system was devised. The system consisted of a camera and an illuminated target with a series of black and white stripes oriented parallel to the axis of the lower tear meniscus. The target was mounted on a flash gun close to the objective of a Brown macrocamera and calibrated using a graduated series of glass capillaries of known diameter, ground down to expose the inner wall. It was then applied to normal human eyes (n=45) to measure the tear meniscus curvature. A video system was also assessed which provided qualitative online information about the tear meniscus.
RESULTS—Using the photographic system, measured values for capillary radii were in excellent agreement with theoretical calculations (r2=0.996, p<0.0001). The radii of curvature of lower tear menisci in normal human subjects (mean 0.365 (SD 0.153) mm, range 0.128-0.736; n=45) were similar to those reported in the literature. Both systems demonstrated variations in meniscus shape. The video system provided stable images of human menisci over prolonged periods of time and promises to be useful for the analysis of dynamic changes in meniscus volume.
CONCLUSIONS—Reflective meniscometry is a non-invasive technique providing quantitative information about tear meniscus shape and volume and of potential value in the study of ocular surface disease.

 Keywords: tear meniscus; reflective meniscometry; radius of curvature; tear kinetics

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Figure 1  .

Figure 1  

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Front view of the photographic system, consisting of the target and a Brown macrocamera.

Figure 2  .

Figure 2  

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Diagram of the photographic system. E=subject's eye; M=Brown's macrocamera; T=target; F=flash; A=flexible arm.

Figure 3  .

Figure 3  

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Diagram of the video system. E=subject's eye; L=lens; T=target; S=light source; C=video camera; R=video recorder; M=monitor.

Figure 4  .

Figure 4  

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(A) Relation between measured and theoretically derived radius of curvature of an individual capillary tube target. Excellent agreement is shown: (y=0.0300+0.936x (r2=0.996, p<0.0001); where x = theoretical (mm), y = measured (mm)). (B) Image formed by a ground down glass capillary tube (radius 0.547 mm; bar=500 µm).

Figure 5  .

Figure 5  

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A representative example of the normal meniscus of a human eye. Measurement is made in the region of the central part of the lid where the images of the target lines are usually parallel (see text; bar=500 µm).

Figure 6  .

Figure 6  

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Scatter plot of measured radius of curvature against age of subject.

Figure 7  .

Figure 7  

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Representative examples of variations in the meniscus shape; (A) forward serrations, (B) doubling; bars=500 µm.

Figure 8  .

Figure 8  

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Example showing the change in the tear meniscus curvature, after instillation of a single drop of Celluvisc (1% carboxymethylcellulose sodium, Allergan). Ordinate: Stripe width measured directly from the TV monitor using a multistripe target. The width of three black and white cycles is shown. Abscissa: Time in minutes. Average width (mm) (SD) (error bars are hidden by the symbols at 3, 10, and 12 minutes).

Figure 9  .

Figure 9  

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Ray diagram for theoretical determination of the radius of meniscus curvature. T=target; C=centre of the expected circular portion of the meniscus; I=image; F=focal point of the convex meniscus mirror; u=target distance; v=image distance; r=radius of meniscus curvature; f=focal distance.

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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