This article was originally published in a sponsored newsletter.

When SLs are applied to the ocular surface the physical properties of the fluid are altered, which impacts tear composition and concentration.²Midday fogging is a common complication of SL wear in which debris accumulates in the fluid reservoir during lens wear and has been reported in up to 46% of SL wearers.² Midday fogging may reduce vision and cause other physiologic complications.²
 
A novel study evaluated 13 neophytes (26 eyes, 69% female, 28 ± 9 years old) to wear custom SLs for four days to determine correlations between lipids in the fluid reservoir and the severity of midday fogging.²Anterior segment optical coherence tomography was utilized to quantify lens vault and midday fogging. The fluid reservoir was collected and analyzed by liquid chromatography–tandem mass spectrometry. Nonparametric correlation testing (Spearman rank) was used to assess the relative abundance of lipids compared to midday fogging scores.
 
Participants were examined after eight hours on days 1 and 4. Midday fogging severity was 33 ± 29 units on day 1 and 28 ± 24 units on day 4 (r = 0.94; p < 0.01) at the eight-hour time point of SL wear. A total of 170 distinct lipid species were detected and the lipid classes with greatest correlation to midday fogging were the wax esters, cholesteryl esters, and triacylglycerols.
 
Nonpolar lipids were the greatest contributors to midday fogging. This study reinforces the presence of several lipid classes and species in the fluid reservoir during SL wear and proposes that nonpolar hydrophobic lipids, especially wax esters, cholesteryl esters, and triacylglycerols, contribute to midday fogging. It was also proposed that cellular debris exists in the fluid reservoir independent of midday fogging severity due to the finding of lipids common to cell membranes (phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin). These hydrophobic lipids appear to collect in the SL fluid reservoir in susceptible patients, most likely originating from the meibomian glands, and are associated with the increasing turbidity that occurs in midday fogging.
 
Of interest, polar lipids were present in a greater proportion than expected and were not correlated to midday fogging. An example are phosphatidylcholine lipids, which comprise 0.015% to 0.2% of total natural tear lipids, were 50% to 90% of total lipids detected in the fluid reservoir.² Polar lipids may be attributable to cellular debris, although they do not appear causative to midday fogging. No measured ocular surface or fitting values were correlated to midday fogging. 
 
Future studies investigating other tear fluid components such as cells, proteins, and metabolites will help to develop a full appreciation of the complex fluid reservoir environment with and without midday fogging.

REFERENCES

1. Wizert A, Iskander DR, Cwiklik L. Organization of lipids in the tear film: a molecular-level view. PLoS One. 2014 Mar 20;9:e92461.
2. Walker MK, Bailey LS, Basso KB, Redfern RR. Nonpolar Lipids Contribute to Midday Fogging During Scleral Lens Wear. Invest Ophthalmol Vis Sci. 2023 Jan 3;64:7.

Melissa Barnett, OD, FAAO, FSLS, is a principal optometrist at the University of California Davis Eye Center in Sacramento, specializing in anterior segment disease and specialty contact lenses. She is the past president of the Scleral Lens Education Society. She is an advisor to and/or has received honoraria or travel expenses from AccuLens, Alcon, Allergan, Bausch + Lomb, Bruder, Contamac, CooperVision, EveryDay Contacts, Johnson & Johnson Vision, Mojo Vision, Ocusoft, ScienceBased Health, Shire, SynergEyes, Tarsus, and Visus Therapeutics.