Tear Film Lipid Layer Has Unique Characteristics Across Types of Meibomian Gland Dysfunction

Evaluating the thickness of tear film lipid layer (TFLL) in meibomian gland dysfunction (MGD) using a high-resolution optical microscope found that those with MGD and a group with mixed Ocular Surface Disease Index (OSDI) and meibum grade score (MGS) had the largest percentages of TFLL thicknesses in the thinnest modes (peak 34.3 and 33.8 nm, respectively), according to a study published in The Ocular Surface.

“These data show that measures of central tendency (e.g., averages, medians) do not fully appreciate the variable distributions of TFLL across disease spectra,” study authors report.

In the study, 190 patients were divided into four groups using the OSDI and MGS: Normal (OSDI<13 and MGS<10), mixed (OSDI≥13 and MGS<10), asymptomatic MGD (OSDI<13 and MGS≥10), and MGD (OSDI≥13 and MGS≥10). Researchers used a high-resolution optical microscope to take TFLL images in vivo. Histograms of TFLL thickness were then analyzed and curve-fitted with probability density functions (PDFs).

They found 3 obvious peaks in the distributions of TFLL across the groups. Using the curve-fitting process, main outcomes were displayed according to Gaussian functions using the position of peak (μ) and the summed percentage within the range of standard deviation (σ). Distribution for the normal group was: 33.3±0.005 nm, 26%; 53.9±0.019 nm, 40%; 79.4±0.064 nm, 12%. For the mixed group: 33.8±0.004 nm, 32%; 53.1±0.115 nm, 21%; 71.7±0.232 nm, 27%. For the asymptomatic MGD group: 33.5±0.004 nm, 20%; 49.2±0.041 nm, 25%; 62.9±0.063 nm, 47%. And finally, for MGD group: 34.3±0.004 nm, 34%; 53.7±0.022 nm, 28%; 74.9±0.060 nm, 16%.

“The novel high-resolution microscopy used herein has permitted a closer examination of the thickness distribution of TFLL in the context of MGD. When combined with contemporary biochemical techniques to analyze the lipid components of the TFLL and other methods to evaluate the stability of TFLL, the current imaging system may further advance the understanding of role of the TFLL structure and function in health and disease,” researchers explain.

Reference

Bai Y, Ngo W, Khanal S, Nichols JJ. Characterization of the thickness of the tear film lipid layer in meibomian gland dysfunction using high resolution optical microscopy. Ocul Surf. 2021;24:34-39. doi:10.1016/j.jtos.2021.12.011.