Original ResearchInfluence of Conjunctival Folds on Calculated Tear Meniscus Volume Along the Lower Eyelid
Introduction
The tear fluid on the ocular surface is present in three sections: at the exposed area between the lids covering the cornea and sclera, in the tear menisci at the lid margins, and in the conjunctival sacs of the upper and lower lid.1 The tear menisci along the superior and inferior lid margins represent 75% to 90% of the tear film volume at the ocular surface,2 although a lower estimate of 27% has been made.1 The shape of the lower central meniscus is described to be roughly wedge-shaped in sagittal section, with a concave anterior surface, and posterior and peripheral surfaces that bathe and moisten the hydrophilic mucosae of the cornea and bulbar conjunctiva or palpebral conjunctiva.3 However, the cross-sectional profile of the meniscus is likely to have a more complex shape,3 with a parabolic anterior profile4 and a posterior surface that is influenced by the shape of the underlying conjunctiva at the paracentral lid locations.5
At the central lid location, the evaluation of tear meniscus parameters is regarded as an indicator of tear film volume.6, 7 The tear meniscus can be characterized by tear meniscus height (TMH), tear meniscus radius (TMR) or cross-sectional tear meniscus area (TMA), and these have been shown to be significantly correlated to one another at the central point of the tear meniscus.8, 9, 10, 11 For paracentral positions along the lower eyelid, however, the relationship between meniscus height, radius, and cross-sectional area has not yet been published.
The volume of the tear meniscus (TMV) has traditionally been calculated from TMH, TMR or TMA of the central lower tear meniscus multiplied by the length of the lid margin.12, 13 Since the meniscus is spread along the eyelid margins, variations in the measured meniscus parameters along the lid are likely to influence the calculation of the lower lid tear meniscus volume. Lid parallel conjunctival folds (LIPCOFs) are folds in the inferotemporal and inferonasal quadrants of the bulbar conjunctiva, parallel to the lower lid margin. LIPCOFs can be observed with the slit lamp or by optical coherence tomography (OCT), and they have been found to correlate with dry eye symptoms.5, 14, 15, 16, 17, 18, 19 Like conjunctivochalasis, LIPCOFs are assumed to alter the measurement of the tear meniscus area.16, 18, 20, 21
Using a portable digital meniscometer (PDM), it was shown that an increase in LIPCOF grade is associated with a higher TMH and a larger TMR at the nasal and temporal locations of the tear meniscus.22 Furthermore, it was suggested that LIPCOFs also impact the central TMH evaluation, and that the presence of LIPCOFs may cause the central TMH measurement to overestimate the actual central tear meniscus volume.23 However, TMH and TMR measurements are limited to one dimension and describe only the anterior surface of the tear meniscus; they do not account for the posterior section of the meniscus, so the extent of the LIPCOFs is likely to influence the cross-sectional TMA.
Consequently, the aims of this study were: 1) to investigate the influence of LIPCOFs on TMH, TMR and on TMA, measured by OCT at the central and paracentral position of the lower lid, and 2) to analyze the influence of LIPCOFs on the calculated tear meniscus volume at the different locations.
Section snippets
Subjects
Forty-two subjects (13 male, 29 female) were randomly selected from the staff and students of the Höhere Fachschule für Augenoptik Köln (Cologne School of Optometry), Cologne, Germany. The mean age of the subjects was 27.3 ± 8.4 (SD) years (range, 20-67 years). Subjects were excluded if they were pregnant or breast-feeding; had a current or previous condition known to affect the ocular surface or tear film; had a history of previous ocular surgery, including refractive surgery, eyelid
Differences between Tear Meniscus Parameters with Location
Mean values and standard deviations for the tear meniscus parameters at the different locations are summarized in Table 2. Compared to TMH measured in the central location, TMH at the temporal location was 0.088±0.102 mm higher, and at the nasal locations was 0.044±0.081 mm higher (P<.001). Temporal TMH was also found to be 0.044±0.130 mm higher than nasal TMH (P<.05). Compared to TMR measured in the central location, TMR at the temporal location was 0.063±0.061 mm larger (P=.009). However, no
Discussion
The principal aim of the study was to use OCT to investigate the influence of LIPCOFs on TMH, TMR, and for the first time on TMA (and therefore TMV), at the central and paracentral positions along the lower lid margin. For the central TMH, an increasing height was correlated to LIPCOF sum. This is in concordance with a recently published study in which digital slit lamp images were used to measure the central tear meniscus.23 Furthermore, the high-resolution, cross-sectional OCT images used in
Conclusion
Using OCT tear meniscus parameters, it has been possible to investigate the influence of LIPCOFs on TMH, TMR, and for the first time on TMA at the central and paracentral positions on the lower lid. The presence of LIPCOFs results in an irregularity of the tear meniscus along the lid length, and it is also associated with a variation in the relationship between tear volume and tear meniscus height or radius.
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Disclosures: The authors have no commercial or proprietary interest in any concept or product discussed in this article.
Single-copy reprint requests to: Stefan Bandlitz, PhD (address below).