Light transmission/absorption characteristics of the meibomian gland - PubMed (original) (raw)
Light transmission/absorption characteristics of the meibomian gland
Ho Sik Hwang et al. Ocul Surf. 2018 Oct.
Abstract
Purpose: While meibography has proven useful in identifying structural changes in the meibomian gland (MG), little is known regarding the MG spectral transmission and absorption characteristics. The purpose of this study was to measure the transmission/absorption spectra of the MG compared to other eyelid tissues.
Methods: Human and rabbit eyelids were fixed in paraformaldehyde, serial sectioned (50 μm) using a cryotome and imaged by brightfield and reflectance microscopy. Eyelid regions (MG, muscle, tarsus and dermis) were then illuminated by a 100 μm spot using a infrared enhanced white light source. Transmission spectra over a 550-950 nm range were then measured using a spectrometer and differences compared using two-way analysis of variance.
Results: Brightfield microscopy of both human and rabbit eyelid tissue showed a marked decrease in light transmission for MG acini compared to other eyelid tissues. In rabbit, the dermis showed 5× and the muscle showed 2× more light transmission compared to MG (P < .001 and P < .001, respectively). For human, the muscle showed 14× and the tarsus showed 84× more light transmission compared to MG (P < .01 and P < .001, respectively). No specific spectral region of light absorption could be detected in either rabbit or human MG. Loss of light transmission in MG was localized to acini containing small lipid droplets, averaging 2.7 ± 0.8 μm in diameter.
Conclusions: The data suggest that light transmission is dramatically reduced in the acini due to light scattering by small lipid droplets, suggesting that Meibography detects active lipid synthesis in differentiating meibocytes.
Keywords: Light transmission; Meibography; Meibomian gland; Meiboscopy.
Copyright © 2018 Elsevier Inc. All rights reserved.
Figures
Fig. 1.
Measurement of eyelid tissue optical transmission. A. Light from a broad spectrum, white light source was focused on a 100 μm diameter pinhole, and light collimated and focused onto the eyelid tissue through a reflecting mirror. Light passing through the eyelid tissue was then reflected to fiber optic cable connected to a spectrometer. B. Reflected light image of rabbit eyelid tissue section showing a 100 μm illuminated spot (Red arrow) that covered the area of a single acini.
Fig. 2.
Brightfield microscopy of the eyelid. A. Rabbit eyelid showing very dark, acinar regions (arrow) indicating markedly decreased light transmission through the tissue section. Other areas showing increased light transmission compared to the acini were the central duct (asterisk), dermis (arrowhead) and orbicularis muscle (M). B. Note that the area adjacent to the acini in the region of disintegrating meibocytes releasing meibum into the short ductules (small arrows) showed increased transmission of light compared to the acini. C. Human eyelid showing similar loss of light transmission through the acini, and increased light transmission through the central duct (asterisk), tarsus (arrowhead) and orbicularis muscle (M).
Fig. 3.
Reflectance microscopy of rabbit (A) and human (B) eyelid tissue section. Note the marked scattering of light from acini (arrow) in both the rabbit and human meibomian gland. Substantially less scattering was detected from the meibomian gland duct (asterisk), dermis in the rabbit (arrowhead), tarsus in the human (arrowhead) and orbicularis muscle (M).
Fig. 4.
A. Spectral intensity curve for the infrared enhanced light that was passed through a glass side, PBS and coverslip. This spectrum was used as a control for measuring the percentage of light transmission through the different eyelid tissue sections. B. Percent transmission of light for rabbit eyelid tissue regions as a function of wavelength from 550 nm to 950 nm. Note that there was very low light transmission in the different regions, with the lowest transmission detected for the acini at less than 0.5%/wavelength and the highest was skin at 3% transmission at 925 nm. C. Percent transmission of light for human eyelid tissue regions. Note that like the rabbit, the acini region shows almost no transmission of light. In contrast, other regions including the muscle and tarsus show greater transmission of light compared to the rabbit eyelid.
Fig. 5.
Brightfield (A) and fluorescent imaging (B and C) of LipidTox stained human eyelid tissue showing presence of small lipid droplets in regions of diminished light transmission within the meibomian gland acini.
Fig. 6.
Brightfield image of thick rabbit eyelid tissue section before (A) and after (B) acetone extraction. Note that acinar regions show marked increase in light transmission after acetone treatment and extraction of lipid from intracellular droplets. No change in light transmission was detected for other tissue regions including the eyelid cilia (arrow).
References
- Lemp MA, Crews LA, Bron AJ, Foulks GN, Sullivan BD. Distribution of aqueous-deficient and evaporative dry eye in a clinic-based patient cohort: a retrospective study. Cornea 2012;31:472–8. -PubMed
- Lemp MA, Nichols KK. Blepharitis in the United States 2009: a survey-based perspective on prevalence and treatment. Ocul Surf 2009;7:S1–14. -PubMed
- Tong L, Chaurasia SS, Mehta JS, Beuerman RW. Screening for meibomian gland disease: its relation to dry eye subtypes and symptoms in a tertiary referral clinic in Singapore. Invest Ophthalmol Vis Sci 2010;51:3449–54. -PubMed
- Jester JV, Nicolaides N, Smith RE. Meibomian gland studies: histologic and ultrastructural investigations. Invest Ophthalmol Vis Sci 1981;20:537–47. -PubMed
- Mathers WD. Ocular evaporation in meibomian gland dysfunction and dry eye. Ophthalmology 1993;100:347–51. -PubMed