Tear film dynamics and lipid layer characteristics—Effect of age and gender
Introduction
Dry eye is a common and increasingly prevalent condition in people over 50 years of age [1]. Many epidemiology studies have identified age and female gender as risk factors in dry eye disease [2], [3], [4], [5], [6], [7], [8]. Recently a Spanish epidemiology study showed that dry eye is generally more frequent in women than in men and associated with aging [8]. Further, as part of the Australian epidemiology study, McCarty et al. reported, a significant decrease in tear production in women 50–59 years of age in addition to an increased prevalence of dry eye with age [7].
Whereas there is a general consensus in the dry eye epidemiology literature as to the higher prevalence of dry eye disease with aging and in particular in women, the effect of advancing age and gender on tear functions is less clear.
Mathers and Lane [9] have shown a decline in tear film functions with age; the tear flow and tear volume decrease with age, whereas, tear film evaporation and tear osmolarity increase. However, other studies have shown no effect of age on tear film evaporation [10], [11], stability [12], [13] or tear lipid layer characteristics [12], [13], [14].
Dry eyes have been classified in two major groups by the 2007 DEWS report [15] based upon their aetiology: aqueous tear-deficient dry eye (ATDE) and evaporative dry eye (EDE). Evaporative dry eyes have been associated with meibomian gland dysfunction leading to lipid insufficiency and/or poor lipid spreading. Regardless of the aetiology of the lipid anomaly the result is a failure to form a continuous and homogeneous film, leading to increased evaporation and decreased tear film stability [16], [17], [18], [19], [20].
The main function of the lipid layer is to provide an outer hydrophobic barrier [21] to prevent the evaporation of the aqueous phase [16], [22], [23]. In the absence of an outer oily layer, the tear film evaporation rate is 10–20 times greater [23]. More recently Craig and Tomlinson reported that an absent or non-confluent lipid layer was associated with a four-fold increase in evaporation rate [16]. A thick and homogeneous lipid layer, characterised by a visible amorphous pattern during slit-lamp examination with the Tearscope [24], is associated with the greatest tear film stability.
The prevalence of meibomian gland dysfunction (MGD) is high, at around 39%, in a population of non-contact lens wearers and increases with age [9], [25], [26], [27]. Treating meibomian gland anomalies has been proven successful at decreasing symptomatology both with and without contact lenses [28], [29] increasing tear break up time [28], lipid layer thickness [30] and stability [31].
The stability of the tear film has been shown to be different in dry eye sufferers [32] and in 2007, the DEWS workshop [15] has specified tear film instability as an integral part of dry eye disease: “Dry eye is a multifactorial disease of the tears and the ocular surface that results in symptoms of discomfort, visual disturbance, and tear film instability with potential damage to the ocular surface”.
It is therefore postulated that the greater prevalence of dry eye problems with aging is at least in part related to poorer tear film dynamics, in particular lipid layer related features.
The hypotheses tested were that the tear film dynamics, in particular lipid related characteristics, in the over 45 years of age are poorer than in younger people and among the older group they are worse in women than men.
Section snippets
Materials and methods
The in vivo evaluation of the tear film characteristics was carried out using a slit-lamp observation system (SLD7 Topcon digital slit-lamp magnification 6–40×) with the Tearscope lighting system allowing the different layers of the tear film to be visualised non-invasively under a 16–25× magnification.
The lipid layer was observed over the whole corneal surface; the mixing patterns observed within the lipid layer were classified based upon their appearance as described by Guillon and Guillon
Study population
A total of 218 subjects took part into the investigation; they were divided into two groups based upon their age: <45 years (n = 160) and ≥45 years (n = 58). The demographics of the sample are presented in Table 1. Each group was further divided based upon gender for the analysis. Two groups were well matched with, however, a trend towards slightly more female subjects in the older group 55% vs. 49% (p = 0.131).
Non-invasive break up time
The study population overall median non-invasive break up time (NIBUT) was representative
Discussion
The current study established that patients’ age and gender are significant factors that influence tear film lipid layer characteristics and tear film dynamics.
The tear film characteristics were shown to worsen with age. The 45 years and over age group had a thinner and more contaminated lipid layer, and a less stable tear film than the younger group. The current findings of the effect of advancing age on tear film stability are in agreement with recent studies from Ozdemir and Temizdemir on
Conclusion
Aging of the tear film is characterised by its destabilisation associated with significant changes in the tear lipid layer leading to less protection from evaporation in the aging population; the observed changes are more marked in women than in men.
The findings have significant implications for the management of older dry eye sufferers, for whom decreasing evaporative problems is essential. Further the gender of the subject should be taken into consideration during clinical examination and
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2022, Journal of OptometryCitation Excerpt :Despite evidence that the use of SG prevents the detrimental effects of swimming pool chlorine on the corneal epithelium,23 these results suggest that SG wear may have a negative impact on tear film stability, as assessed by TFSQ-BUT. Leaving aside the personal characteristics (e.g., age or gender) and lifestyle habits as factors associated with DED,49 the TFSQ-BUT has demonstrated to be altered by multiple causes such as wearing contact lenses, computer work, adverse environmental conditions (e.g., low humidity, air conditioning, pollution), medication use, and refractive or cataract surgery among others.4–18 In addition, these data revealed that SG wear acutely diminishes tear breakup time, suggesting that the use of SG leads to tear film disruption and possible ocular surface damage.