In this study, machine learning models were trained to take subject characteristics, lifestyle behaviors and risk exposures, clinical assessments of the ocular surface, tear film and eyelids, and symptom scores from validated DE instruments, and combine them in prediction models of DE-related outcomes. Lifestyle factors were found to be among the most heavily weighted features used by the models to predict a number of clinical signs, subjective symptoms, and diagnoses related ocular surface disease. Prediction accuracies for DE-related symptoms ranged from 60.7–86.5%, for diagnoses from 73.7–80.1%, and for clinical signs from 66.9–98.7%.
Greater age was a heavily weighted predictor for clinical signs including the presence of eyelid notching, anterior displacement of the LoM, and shorter FTBUT among Asian subjects. Greater age was also a heavily weighted predictor for VAS dryness severity and frequency ratings, both throughout the day and at end-of-day, as well as for a clinical diagnosis of blepharitis. There is evidence to suggest that the LoM can shift due to aging, and due to the presence of DE.14,18 Eyelid margin irregularities such as notching are frequently observed in cases of blepharitis and MGD,19,20 both conditions known to be related to aging.21–24 It has been well documented that symptoms of DE and MGD are on average more severe, frequent, and prevalent among older populations.22,25–27
More years of CLW was a heavily weighted predictor in models of LWE, a thinner lipid layer, a higher SPEED II score, and a diagnosis of MGD, all of which are in agreement with the literature.28–32 In general, however, the interclass differences in these models were very small (0.2–1.4 yrs of CLW). Similarly, CLW frequency (days/wk) was a heavily weighted predictor of unstable vs. stable FTBUT33 but with small interclass differences (0.4–0.5 days/wk). These results illustrate how very small differences that are not considered to be of importance to clinicians can still be heavily weighted features in machine learning predictions.7
Duration of CLW (hrs/day) was a heavily weighted feature in predicting FTBUT among Asian subjects. In contrast, while the duration of comfortable CLW (hrs/day) was not a heavily weighted predictor for any clinical signs, it was an important predictor for every subjective measure of symptoms studied.34 Asymptomatic subjects averaged 0.8–4.4 more hrs/day of comfortable CLW. Total hrs/day of CLW is not always informative because corneal desensitization, wearer commitment, lifestyle needs, and individual pain sensitivity level can result in continuing wear far beyond the onset of symptoms. Hrs/day of comfortable CLW was a far better predictor of symptoms. Clinicians should ask symptomatic contact lens patients about their comfortable wearing time and distinguish it from their total wearing time.35
It is important to point out that with these machine learning prediction models the direction of causality is generally unknown, but sometimes can be inferred logically. For example, there was longer CLW duration (hrs/day) among Asian subjects with shorter FTBUT. Other than by chance (e.g., some unknown sampling bias), there is no reason to think that better tear film stability would cause contact lens wearers to wear their lenses less. The fact that those with shorter FTBUT were actually wearing their lenses longer implies that the direction of causation is from longer CLW to shorter FTBUT and not the reverse.
Amount of near work (hrs/day) was a heavily weighted predictor of eyelid margin erythema among all subjects and shorter NITBUT among Asian subjects. Subjects with erythema or reduced tear film stability averaged slightly over an hour per day more near work. Frequent near work is a well-known risk factor for DE, particularly in the context of digital display use.36–38 While there is little information on the effects of near work on the eyelids, Wu et al. found that an eyelid margin abnormality score was positively correlated with time using a visual display terminal, and that FTBUT, corneal staining, and OSDI score were all significantly worse in a cohort using visual display terminals for more than 4 hours per day.39 Most studies of near work and tear film stability have employed FTBUT as the outcome measure. Khezrzade et al., however, did find that NITBUT was significantly reduced after 30 minutes of reading.40 To our knowledge, the machine learning results presented here represent the only other evidence of the effects of sustained near work on non-invasive measurements of tear film stability, and that sustained near work may ultimately have effects on the eyelid margin.
Consuming caffeinated beverages was a heavily weighted predictor only for CLDEQ-8 score, and only with an average of 0.2 drinks per day more among those with a higher score. Caffeinated beverage consumption was not predictive of any other signs, symptoms, or diagnoses. Most studies have found either no relationship between caffeine consumption and DE,41 or a possible protective effect.1,42,43 Consumption of alcohol on the other hand was a heavily weighted predictor of poor meibum quality and of worse DE symptoms on several questionnaire instruments. Subjects with poor meibum quality averaged 1.0 drink more per week, and symptomatic subjects averaged 1.0-1.3 drinks more per week. Although the effect size appears to be small, it should be kept in mind that it is equivalent to 52–68 drinks more over the course of a year. The literature on the effects of alcohol on the signs and symptoms of DE is largely equivocal.1 Some studies have found alcohol consumption to be linked to tear film deterioration, reduced tear volume, increased osmolarity, and worse DE symptoms.43,44 Other studies have found alcohol to be a non-factor in DE, 42,45,46 and a few studies have reported a protective effect against DE.41,47 To our knowledge this is the first study to link alcohol consumption to lower quality meibum. Magno, et al. found that alcohol consumption significantly increased the risk of DE in women but not in men, possibly due to differences the hormone androgen, the deficiency of which has been linked to MGD.44 In men, it has been shown that excessive or chronic alcohol consumption can reduce serum testosterone.48 Modeling the interaction of alcohol consumption and sex was not performed in this study and may deserve further investigation.
More time exercising was found to be a heavily weighted predictor of less LWE. LWE is associated with sub-clinical inflammation,49 and exercise has been linked to reduced tear concentrations of several cytokines and other markers of inflammation or oxidative stress.50–52 Aerobic exercise has been shown to promote tear secretion and improves tear film stability in dry eye patients,50,53 and tear film instability has been linked to LWE.28 Other studies have also demonstrated a link between a lack of exercise (i.e., sedentary lifestyle) and risk of DE. Sedentary behavior has been associated with reduced tear breakup time, lower tear volume, and risk of DE.50–53 It has been speculated that exercise increases parasympathetic stimulation of the lacrimal gland and acinar blood vessels, increasing secretion of electrolytes and aqueous.1
Approximately 2.5 hours more per week spent outdoors was found to be a heavily weighted predictor of lesser corneal staining extent, and of lower CLDEQ-8 score among contact lens wearers. Some studies have found time outdoors to be a risk factor for DE,46,54 often related to extreme heat or cold conditions38 or excessive wind.55 Other studies have found time spent outdoors to be a non-factor in risk for DE.45 Rodriguez, et al. found that time spent on indoor work was associated with a decreased blink rate,56 which is well known to be an etiological factor in DE. In this study, a post-hoc analysis showed that our subjects who spent more time outdoors were also doing less near work on average (thus presumably blinking more), and exercising significantly more.
More time riding the train was a heavily weighted predictor of higher OSDI score. More time driving a car was a heavily weighted predictor of higher symptom scores including OSDI score, VAS ratings, and DEFC classification. Symptomatic subjects averaged 0.8-3.0 more hours per week exposure. There are likely similarities and differences in the mechanisms of DE symptoms in these two types of exposure. While there are studies on how DE affects the ability to drive,26 there are relatively few studies of car driving or train riding as a causative or risk factor for DE. Guillon, et al. found a greater incidence of symptoms among DE subjects after riding the subway and after driving a car for both contact lens wearers and non-wearers.57 Rodriguez, et al. found increased levels of ocular discomfort and a reduced interblink period associated with driving a car.56 The link between DE and these exposures could be due to the inside environment (e.g., windows open or closed; heater or air conditioner settings; fan settings; environmental contaminants or cleaning product irritants), which could apply to both cars and trains. It could also be due to extended visual tasking while driving for extended periods which reduces the interblink period,56 while extended visual tasking at distance would likely not apply to riding the train.
The limitations of this study include employing univariate logistic regression in the machine learning prediction models. More sophisticated statistical models and larger datasets for some sparse variables are likely to improve prediction accuracy further, especially for symptoms. There are numerous other likely important lifestyle behaviors and exposures that were not addressed in this study, including obesity, dietary habits, health and wellness supplements, sleep patterns, and a wide variety of ocular and systemic medications, to name a few. Future work would also benefit from modeling interactions among demographic and risk factors to determine if predictive relationships are the same for different ages, sexes, and races.