There are approximately 140–150 million contact lens (CL) wearers worldwide.1,2 Approximately 30% to 50% of CL wearers report dry eye (DE) symptoms.3,4 The Tear Film & Ocular Surface Society Dry Eye Workshop II (TFOS DEWS II) reported that CL wear increases the risk of developing DE by about 2–4 times.5,6 CL induced ocular changes leading to DE disease include tear film instability,3 increased tear evaporation rate and tear osmolarity7 and decreased tear film meniscus volume.8 DE and tear film changes in CL wearers are related to reduced visual acuity, decreased wear time,9 and are a major causative factor for discontinuation of lens wear.10

In addition to DE, CL use may induce complications such as keratitis, giant papillary conjunctivitis, infections3 and corneal disorders.7,11–13 CL wear has also been shown to be correlated with changes in meibomian gland (MG) morphology and function.2,4,10

Meibomian gland dysfunction (MGD) has been defined by the subcommittee of The International Workshop on MGD as a chronic and diffuse disorder that occurs in MGs. MGD is characterized by glandular orifice obstruction and/or changes in the quality and/or quantity of meibum that is secreted by the MGs. It may affect the tear function, causing evaporative DE, and also evoke symptoms of ocular discomfort.14 Furthermore, MGD has been associated with the cessation of CL wear.15

Key signs of MGD include plugged MG orifices and MG dropout.16 Eyes with MGD exhibit altered MG secretion that is turbid or cloudy, and tears that are frothy or foamy.17 Numerous structural changes occur, including thickening, rounding or irregularity of the lid, displacement of the mucocutaneous junction, vascular dilatation, telangiectasia,18 madarosis or trichiasis,19 and notching of the lower lid margin. 17

MGD is one of the most common diseases observed in ophthalmic and optometric clinics.20 Five pathophysiological mechanisms have been suggested: eyelid inflammation, conjunctival inflammation, corneal damage, microbiological changes and DE disease.21

In 2011, the International Workshop on MGD created a consensus of diagnostic criteria for the condition.16 These criteria include a questionnaire based assessment of symptoms, along with functional and morphological measurements. Functional aspects include meibum expressibility and quality, and tear production (Schirmer test). A tear quality assessment should be performed, consisting of blink rate and interval, tear meniscus height, tear osmolarity, tear-film breakup time, and corneal and conjunctival fluorescein staining. Morphological aspects include quantification of specified lid features and meibography.16 The Osmoprotection in Dry Eye Disease- Expert Opinion (OCEAN) group updated these diagnostic criteria in 201722 by adding functional diagnostic technologies such as interferometry, non- invasive tear film breakup time measurement, and a morphological assessment using in vivo confocal laser microscopy. Despite the international effort to create standardization in the diagnosis of MGD, the criteria are not often used in research, resulting in different definitions in various studies.23

Studies regarding the relationship between MGD and CL wear are inconclusive, some demonstrating a significant relationship between MGD and CLs,2–4,10,24–34 and others concluding that there is no significant relationship between MGD and CLs.7,35–40 This work aims to review the scientific literature regarding the effect of CL wear on MGD and to offer an objective approach to address the question in the future.

A Pubmed database search for research papers written in English between 1980 and 2021 was conducted. Primary search terms and their synonyms were used singly or in combination, including “meibomian gland,” “meibomian gland dysfunction,” “contact lens” and “dry eye", without Boolean operators. Studies whose purpose was to examine the structural and/or functional changes of the MGs in CL wearers were considered relevant and included. Searches were also performed for articles referenced in bibliographies that were not initially retrieved by the search.

The database search resulted in 115 papers, of which 22 were pertinent to the topic of this review. Of these 22 studies, 15 showed an association between MGD and CLs2–4,10,24–34 (Table 1) and seven did not (Table 2).7,35–40

Studies tabulated in Tables 1 and 2 used a wide variety of diagnostic criteria, making comparison of the results challenging. Some papers relied on functional assessments alone, while others also used morphological testing, which may better characterize the association of CL wear and MGD. Some papers did not include a control group, which could confound their observations. Thus, the following sections will focus on the studies that used both functional and morphological evaluations and included a control group.

The evidence for the effect of CL wear on the MGs is equivocal. Fifteen studies2–4,10,24–34 (Table 1) reported functional and/or morphological changes in the MGs among CL wearers, with five studies showing significant correlations between the duration of CL wear and MG loss.3,4,24,32,34

Conversely, seven studies7,35–40 (Table 2) did not report an association between CL wear and MGD suggesting that CL wear may not increase the risk of MGD. Of these, four found no correlation between CL wear and poor MG expressibility.35,36,38,39 However, one did find a correlation between CL wear and a higher meiboscore.39 Another examined overnight orthokeratology which differs greatly from other modalities of CLs, and may not be appropriate for assessing the effect of CL wear on MGs.37 Finally, three other studies,7,37,40 which found no effect of CL use on the MGs, did not include a control group of non-CL wearers, limiting these studies’ conclusions.

Discrepancies between studies may be due to differences in the definition of MGD, specifically prior to the 2011 international workshop on MGD.16 They may also stem from differences in the method of evaluation of MGD. For example, while some studies assess DE symptoms using the Contact Lens Dry Eye Questionnaire (CLDEQ),7,10,31,33,40 others used the Dry Eye Questionnaire (DEQ-5),10 or OSDI questionnaire.2,4,10,24,27,32,34,37

While some studies included a large pool of participants (≥100)2,3,7,10,29,30,34,35,38–40 others included small sample sizes4,24–28,31,32,36,37 (Tables 1, 2). Furthermore, studies differ in the inclusion2–4,10,24,30,32,34–36,38,39 vs. exclusion7,25–29,31,33,37,40 of a control group of non-CL wearers.

Studies also vary in the assessment techniques. For example, MG morphological changes were assessed by transcutaneous infrared MG photography,28 noncontact infrared meibography,7,10,37 transillumination observation meibography,32 BG-4M non-contact meibography system,4 Oculus Keratograph 5M Meibo-Scan,31,34,39,40 or scheimpflug imaging.2,24 Some studies examined only the lower eyelid4,7,25,26,28,32,35,36 or only the upper eyelid,27 while others examined both eyelids.2,3,10,24,31,34,39,40

Arita et al.3 reported that the total meiboscores of the upper eyelids were significantly higher compared to the lower eyelids in CL wearers. They suggested that the upper eyelid may experience more mechanical irritation since it completes larger movements during blinking. Therefore, there may be importance in the examination of both lids.

Another inconsistency between studies is the ages of participants which may influence the outcomes (see in Tables 1 and 2). Given that the number of MGs decreases with age,44 studies that do not control for age, can be misleading.

A further source of discrepancy between studies is the CL materials used by participants of different studies. CL materials may affect the physiology of the MGs as a result of constant mechanical interaction between them.27 Arita et al.3 found no significant difference in gland atrophy area between rigid gas permeable and hydrogel CLs wearers, while Llorens-Quintana et al.27 found significant changes in the area of gland atrophy and the number of glands of hydrogel CL wearers as opposed to silicone hydrogel CL wearers. Other studies25,26,35 did not consider CL materials or duration of CL wear, parameters that may affect the results.

Studies conducted in different countries with different ethnic populations (Malaysia,38 Los Angeles,35 Spain,27 Australia,31 Turkey,2 Japan3) may also account for differences in reported outcomes. For example, Asians have an absent or lower crease and more fat in their upper eyelids,45 and produce more secretion from the MGs upon expression compared to Caucasians.38

Additionally, some studies were multicenter clinical trials24,33,39,40 which may be limited by inter-examiner variation in methodology, evaluation and rating of clinical findings.

The results of the studies in Table 1 suggest several pathophysiological mechanisms for loss of MGs in CL wearers. Korb and Henriquez26 and Henriquez and Korb25 suggested that mechanical obstruction in which epithelial cells accumulate into keratotic clusters, block the meibomian duct, thereby changing the oily secretion. In addition, their results suggest that the presence of bacteria and/or their toxins can damage the MGs. Ong and Larke30 suggested that the permanent rubbing of the CLs at the lid margins during blinking may be a source of mechanical trauma to the lids. Arita et al.3 noted that MG shortening in CL wearers began from the distal side, indicating that chronic irritation of the MGs by CLs through the conjunctiva is a major causal mechanism for changes in the glands. Uçakhan et al.2 concluded that MG thickening may be due to friction, mechanical irritation, or as a result of primary or secondary inflammatory changes. Further research is required to elucidate the exact pathway and it may be a combination of mechanical obstruction, microbiological changes and mechanical abrasion by the CL that cause MGD.

Based on our review of the current literature, the effect of CL wear on the MGs is ambiguous and requires further elucidation. Prospective, longitudinal, large cohort, controlled, randomized studies are required to better understand the mechanisms of changes in MG morphology and function of CL wearers. Efforts should be made to include several CL materials, and CL wear-durations, with analysis taking these parameters into account. Furthermore, new studies should adopt the same criteria and techniques to diagnose MGD, such as those suggested by the international workshop on MGD16 or OCEAN group22 and include a control group. In so doing, these studies will efficiently and effectively identify the long-term impact of CLs on MG and MGD.