ABSTRACT

In 1996, a questionnaire was distributed to 4000 Australiancommercial pilots for the quantification of symptoms of dryeye. The 1246 respondents ranged in age from 18–71 years(mean age 40.4 years), and 98.2% were men. Symptoms of dry eye during flight were reported by 901 (72.3%, 95%CI = 69.7–74.8) while only 67 (5.4%, 95% CI = 4.2–6.8)reported dry eye independent of flight. In univariate analyses,the following factors were associated with dry eye in flight:age, use of distance glasses, smoking, average weekly numberof flight hours, type of aircraft usually flown, and normal cruis-ing altitude. In a multiple logistic regression model, only theclass of aeroplane (large jets vs propeller-driven planes)(OR = 1.75, 95% CI = 1.34–2.28) and estimated number offlight hours per week (OR = 1.58, 95% CI = 1.34–1.86) wererelated to dry eye symptoms. In conclusion, self-reportedsymptoms of dry eye are common in Australian pilots and areassociated with aeroplane class and flying time.

Key words: dry eye, pilots, prevalence.

INTRODUCTION

Signs and symptoms of dry eye are more common inwomen, and increase with age.1–6 In the Melbourne VisualImpairment Project, we found that 5.5% of the populationaged 40 years and older report severe symptoms of dry eyenot associated with hay fever.5 Prior research has indicatedthat the increase in dry eye prevalence with age is causedby a decline in tear film function and tear flow.7 Researchconducted in Japan revealed that the use of video displayterminals decreased the maximum interval between blink-ing and thus was related to the development of dry eyesymptoms.8 Furthermore, these researchers showed thatthe blink rate is positively correlated with the tear evapo-ration rate in people with dry eye.9 Some occupationalgroups might be expected to have an increased risk of dry eye symptoms due to an increased blink rate and tear evaporation time.

The purpose of this study was to quantify the self-reported prevalence of the symptoms of dry eye inAustralian pilots and to identify potential risk factors for dryeye in this population.

METHODS

In 1996, a one-page self-administered questionnaire was dis-tributed to all commercial Australian pilots (n = 4000). Thequestionnaire elicited information regarding the usual air-craft operated, the average number of flights per week, theestimated number of hours in flight per week, the normalcruising altitude (feet), current smoking status, use of dis-tance glasses and contact lenses, use of the personal air flownozzle, and use of eye drops. Class of aeroplane was cate-gorized as jet aircraft (class J) versus propeller-driven aero-planes (classes H, R and T). The pilots were asked whetherthey experienced any of the following symptoms associatedwith flight or independent of flight: dryness, burning, itchi-ness, gritty feeling, redness, tearing, discharge, or foreignbody presence.

Data were entered into a Microsoft Excel spreadsheetand verified against the hard copy. Analyses were performedwith S P S S . A square root transformation of the averagenumber of flight hours per week was used to enable para-metric analyses. Univariate analyses included the χ2 and t-test. Stepwise multiple logistic regression was employed todetermine the variables independently related to self-reported dry eye symptoms. P values less than 0.05 wereconsidered to be statistically significant.

RESULTS

Questionnaires were received from 1246 pilots, a 31%response rate. The respondents ranged in age from 18–71years (40.4 ± 8.9 years, mean ± SD) and 98.2% were men.Seventy-seven (6.2%) were smokers, 31 (2.5%) reportedwearing contact lenses while flying and 222 (17.8%)reported wearing glasses for distance correction. Theaverage number of flight hours per week ranged from 0 to 80with a median of 20 h.

Clinical and Experimental Ophthalmology (2000) 28, 169–171

Clinical and Epidemiology

Survey of dry eye symptoms in Australian pilotsDaniel J McCarty PhD and Catherine A McCarty PhDCentre for Eye Research Australia, University of Melbourne, Department of Ophthalmology, Royal Victorian Eye and Ear Hospital, EastMelbourne, Victoria, Australia

■ Correspondence: Daniel J McCarty, Centre for Eye Research Australia, University of Melbourne, Department of Ophthalmology, Royal Victorian Eye and Ear

Hospital, 32 Gisborne Street, East Melbourne, VIC 3002, Australia. Email: dan@cera.unimelb.edu.au

The prevalence of the various symptoms of dry eye is dis-played in Figure 1. The prevalence of the various symptomsassociated with flight was significantly different from that ofthe symptoms independent of flight (all P < 0.001). The twosymptoms most commonly associated with hay fever (itchi-ness and a gritty feeling) were experienced by more pilotsindependent of flight than associated with flight. Dry-ness during flight was reported by 901 (72.3%, 95%CI = 69.7–74.8%), while only 67 (5.4%, 95% CI = 4.2%–6.8%)reported dryness independent of flight. The prevalence ofdryness during flight varied significantly by age group: 76%in ages 18–29, 75.7% in ages 30–39, 71.1% in ages 40–49and 64.5% in ages 50+ (χ2,3 d.f. = 11.2, P = 0.011). Theprevalence of dryness independent of flight was 5.4% anddid not vary significantly by age group (χ2,3 d.f. = 0.10,P = 0.992). Moisturizing eye drops were used by 174 (14%)of respondents. Pilots who wore contact lenses during flightwere significantly more likely to use eye drops than those

who did not (38.7% vs 13.3%, χ2,1 d.f = 16.2, P < 0.001).Pilots who reported symptoms of dryness during flight werealso more likely to use eye drops than those who did not(18.9% vs 1.2%, χ2,1 d.f. = 65.1, P < 0.001).

In univariate analyses (Table 1), the following factorswere associated with self-reported dry eye symptoms inflight: age, gender, use of distance glasses, smoking, averagenumber of flight hours per week, type of aircraft usuallyflown, and normal cruising altitude. Directing the personalairflow nozzle at the face was not associated with self-reported dry eye symptoms(χ2,1 d.f. < 0.001, P = 0.995).All of the significant univariate risk factors were put into a forward stepwise multiple logistic regression model todetermine the independent predictors of dry eye symp-toms. Only class of aeroplane (J vs H, R and T) (OR = 1.75,95% CI = 1.34–2.28) and average number of flight hoursper week (OR = 1.58, 95% CI = 1.34–1.86) were related todry eye symptoms.

170 McCarty and McCarty

Table 1. Factors associated with self-reported dry eye symptoms in Australian pilots during flight

Self-reported dry eye No self-reported dry eye Univariate test statistic, Multivariate odds ratio, (n = 901) (n = 345) P value 95% confidence limit

Mean age (years) 39.8 41.9 t = 3.53, P < 0.001 NSFemale gender (%) 2.2 0.6 Fisher’s exact test, P = 0.054 NA*Current smoker (%) 8.5 0 Fisher’s exact test, P < 0.001 NSUse of distance glasses (%) 16.3 21.7 χ2 = 5.01, d.f. = 1, P = 0.03 NSWeekly flight hours (mean) 18.5 15.8 t = – 6.05, P < 0.001 1.58 (1.34, 1.86)**Type of aircraft usually flown†

H, R, T class (%) 28.7 44.9 χ2 = 29.4, d.f. = 1, P < 0.001 1.00J class (%) 71.3 55.1 1.75 (1.34, 1.86)

Normal cruising altitude 83.7 73.9 χ2 = 15.4, d.f. = 1, P < 0.001 NS≥ 20 000 feet (%)

* Insufficient sample size for female gender (n = 22); ** included as a continuous variable with square root transformation; † class H, Rand T = propeller-driven aircraft, class J = jet aircraft.

Figure 1. Self-reported preva-lence of dry eye symptoms inAustralian pilots.

DISCUSSION

To our knowledge, this is the first study of self-reportedprevalence of dry eye in pilots. We found that the self-reported prevalence of dryness associated with flight wasvery high and was related to the class of aeroplane andaverage number of flight hours per week.

Three previous population-based studies have docu-mented self-reporting of dry eye.3,5,6 In the Salisbury EyeEvaluation, a study of 2520 Maryland residents aged 65–84years, one or more of six dry eye symptoms was reportedoften or all the time by 15% of the cohort, while 20%reported three or more symptoms sometimes, often, or allthe time.3 In the Melbourne Visual Impairment Project, apopulation-based study of eye disease in Melbourne resi-dents aged 40 years and older, 5.1% of the populationreported moderate or severe symptoms of dryness.5 Thisfigure is nearly identical to the 5.4% of pilots in the currentstudy who reported dryness independent of flight and lendsvalidity to the present study results. In a recent study of 598Japanese aged 18 years and older (mean age 35 years), 33%of participants self-reported dry eye and the dry eye was sig-nificantly associated with video display terminal tasks.6 Theself-reported prevalence of dryness in pilots is considerablyhigher than any of these population-based studies.

One possible reason for the increased prevalence ofdryness reported by these pilots during flight is theincreased blink time concomitant with concentration on thejob of piloting. As was mentioned previously, prior researchhas demonstrated that increased blink time is associatedwith the use of video display terminals and can lead todecreased tear function and dry eye.8,9

A potential limitation of this survey is the relatively lowresponse rate. If people who were more likely to experiencesymptoms of dry eye associated with flight were also morelikely to complete the survey, then the prevalence estimatewould be artificially high. Even if this did occur to someextent, the prevalence of dry eye symptoms associated withflight is still very high, especially in comparison with theprevalence of dryness not associated with flight. We con-ducted sensitivity analyses to evaluate the potential bias

introduced by the response rate. If there had been a 90%response rate and all of the initial non-responders reportedno dryness associated with flight, the prevalence of dry eyewould be 25% (95% CL = 23.6, 26.5). If the response hadbeen 75% and the initial non-responders did not reportdryness, then the prevalence would have been 30% (95%CL = 28.4, 31.7). Both of these prevalence estimates are significantly higher than found in the self-reporting of dryeye not associated with flight, in this study (5.4%), and inthe self-reporting of moderate or severe symptoms of dryeye in the population-based Melbourne Visual ImpairmentProject (5.1%).5

These data suggest that pilots frequently experience dryeye symptoms during flight. Further studies are warranted todetermine the severity of dry eye symptoms in pilots and ifdry eye causes functional impairment in pilots, other flightstaff or significant discomfort in the passengers.

ACKNOWLEDGEMENTS

This project was supported by a grant from AlconLaboratories (Australia) Pty Ltd. Dr Daniel McCarty is aNHMRC Postdoctoral Research Fellow. Dr CatherineMcCarty is the recipient of the Wagstaff Fellowship inOphthalmology from the Royal Victorian Eye and EarHospital. The authors acknowledge Dr John Colvin for hiscontributions to the design of the survey.

REFERENCES

1. Khurana AK et al. Indian J. Ophthalmol. 1991; 39: 55–8.2. Schein OD et al. Ophthalmology 1997; 104: 1395–401.3. Bandeen-Roche K et al. Invest. Ophthalmol. Vis. Sci. 1997; 38:

2469–75.4. Schein OD et al. Am. J. Ophthalmol. 1997; 124: 723–8.5. McCarty CA et al. Ophthalmology 1998; 105: 1114–19.6. Shimmura S et al. Cornea 1999; 18: 408–11.7. Mathers WD et al. Cornea 1996; 15: 229–34.8. Nakamori K et al. Am. J. Ophthalmol. 1997; 124: 24–30.9. Tsubota K et al. Arch. Ophthalmol. 1995; 113: 155–8.

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