Quality of Vision Following LASIK and PRK-MMC for Treatment of Myopia.

INTRODUCTION: Femtosecond-assisted thin flap, laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy with mitomycin-C (PRK-MMC) are the two most common refractive surgical procedures used to enhance visual capability in the U.S military. The purposes of the study were to examine effects on quality of vision following LASIK and PRK-MMC using a novel computer-based quick contrast sensitivity function (qCSF) test. MATERIALS AND METHODS: This prospective clinical study included 58 active duty U.S. military service members who elected LASIK (n = 29) or PRK-MMC (n = 29) refractive surgery for myopia (nearsightedness) treatment. Monocular photopic and mesopic quality of vision of the right eyes in spectacle correction preoperatively and unaided right eyes at four postoperative follow-up visits (1 week, 2 weeks, 1 month, and 3 months) were examined using the qCSF device. Two qCSF parameters, area under a log CSF (AULCSF) between 1.5 and 18 cycles per degree, and CSF cutoff acuity (CSF Acuity), were collected using a 50-trial setting at a 4-m testing distance. General linear model (GLM) Repeated-measures Analysis of Covariance was used to examine effects on quality of vision following LASIK and PRK-MMC. Post hoc testing with Bonferroni correction was used for pairwise comparisons, and preoperative cylinder refraction was used as a covariate. Two-tailed independent t-test was used to compare preoperative and postoperative parameters between LASIK and PRK-MMC. Pearson's correlation, Bland-Altman plots, and multiple linear regression were used to examine the relationship among the qCSF and other vision tests. RESULTS: Quality of vision, AULCSF, and CSF Acuity returned to the preoperative baseline at postoperative 2 weeks under mesopic condition and at postoperative 1 month under photopic condition after PRK-MMC. In comparison, photopic and mesopic quality of vision were not significantly different from the baseline at any of the four postoperative visits following LASIK. Changes of CSF Acuity from the baseline after LASIK were significantly better under photopic than mesopic condition by 0.067 ± 0.014 logarithm of the minimum angle of resolution (logMAR); P < .001). Quality of vision was not significantly different between the LASIK and PRK-MMC groups at postoperative 1 and 3 months. When predicting photopic AULCSF (overall model fit R2 = 0.47), 5% contrast acuity (beta = -0.43), visual acuity in 100% contrast (beta = -0.18), and residual refraction in spherical equivalent (beta = 0.20) were significant predictors (P ≤ .001), while high-order aberrations (beta = -0.07, P = .22) were not significant predictors. Visual acuity (beta = -0.12, P = .07) and high-order aberrations (beta = -0.04, P = .58) were not significant predictors of mesopic AULCSF. Bland-Altman plots show that photopic CSF Acuity and visual acuity had a mean difference of 0.19 ± 0.01 logMAR with limits of agreement (LOAs) at -0.01 and 0.39 logMAR. Photopic CSF Acuity and 5% contrast acuity had a mean difference of -0.06 ± 0.01 logMAR with LOAs at -0.33 and 0.21 logMAR. CONCLUSION: Quality of vision recovers at postoperative 1 week after LASIK and at postoperative 1 month after PRK-MMC. The standard black-on-white high-contrast, chart-based visual acuity test is weak in predicting quality of vision. The qCSF detects mild-to-moderate visual changes and is suitable for quality of vision assessment following refractive eye surgery.

Colour vision classification - comparing CAD and CIE 143:2001 International recommendations for colour vision requirements in transport.

PURPOSE: To evaluate the colour vision severity classification standard 'CIE 143:2001 International recommendations for colour vision requirements in transport' (CIE 143:2001), which has become out of date because of the lack of commercial availability of required colour vision tests. METHODS: One-hundred-five subjects had colour vision tested and colour vision severity classified according to a modified CIE 143:2001 algorithm that included pseudoisochromatic plates (Ishihara's test and Hardy Rand Rittler (HRR) 4th edition), Optec 900 lantern and Farnsworth D-15. Subject's results and colour vision severity classification were compared to performance and colour vision severity classification on the computerized 'Colour Assessment and Diagnosis' (CAD) test. RESULTS: According to CIE 143:2001, using Ishihara's test, Optec lantern and Farnsworth D 15, 11 subjects (10%) were category I (normal), 16 (15%) were category II (mild), 48 (46%) were category III (poor), and 30 (29%) were category IV (severe). Classified by CAD score, 10 (10%) were category I, 11 (10%) were category II, 41 (39%) were category III, and 43 (41%) were category IV. The correlation between the two estimates of the severity of colour vision loss (i.e. CIE 143:2001 and CAD) was high, with a Kendall's Tau test of 0.81 (τ = 0.81 p < 0.001). A suggested CIE 143:2001 classification including new CAD score limits improves the classification correlation to 0.90 (τ = 0.90 p < 0.001) for all diagnoses. CONCLUSION: The colour vision severity classification standard 'CIE 143:2001 International recommendations for colour vision requirements in transport', has not implemented new diagnostic tools with better accuracy. We propose three possible revisions to the CIE 143:2001 algorithm, based on the availability of CAD: (1) Replacing the current CIE 143:2001 algorithm using new CAD threshold limits, (2) Use of CAD as a secondary test to Ishihara's test and HRR or (3) Revising the current CIE 143:2001 algorithm using Ishihara's test, HRR, Optec 900 and FD15.

Correlation between observation task performance and visual acuity, contrast sensitivity and environmental light in a simulated maritime study.

PURPOSE: To examine the relevance of visual acuity (VA) and index of contrast sensitivity (ICS) as predictors for visual observation task performance in a maritime environment. METHODS: Sixty naval cadets were recruited to a study on observation tasks in a simulated maritime environment under three different light settings. Their ICS were computed based on contrast sensitivity (CS) data recorded by Optec 6500 and CSV-1000E CS tests. The correlation between object identification distance and VA/ICS was examined by stepwise linear regression. RESULTS: The object detection distance was significantly correlated to the level of environmental light (p < 0.001), but not to the VA or ICS recorded in the test subjects. Female cadets had a significantly shorter target identification range than the male cadets. CONCLUSION: Neither CS nor VA were found to be significantly correlated to observation task performance. This apparent absence of proven predictive value of visual parameters for observation tasks in a maritime environment may presumably be ascribed to the normal and uniform visual capacity in all our study subjects.

Hearing loss in the Royal Norwegian Navy: A longitudinal study.

The aims of this longitudinal study were to investigate a significant threshold shift (STS) among personnel working on board the Royal Norwegian Navy's (RNoN) vessels between 2012 and 2014 and to identify possible determinants of STS. Hearing thresholds were measured by pure tone audiometry in two consecutive examinations (n = 226). STS was defined as an average change in hearing thresholds ≥ + 10 dB at 2,000 Hz, 3,000 Hz, and 4,000 Hz in either ear. Determinants of STS were assessed through a questionnaire. The incidence of STS was 23.0%. Significant determinants of STS were the number of episodes of temporary threshold shifts (TTS) in the Navy, exposure to continuous loud noise during work on board, and the number of gun shots (in the Navy, hunting, and sports). This study indicated a significant association between noise exposure on board Navy vessels and development of STS.

Noise and exposure of personnel aboard vessels in the Royal Norwegian Navy.

Despite awareness of noise aboard vessels at sea, few studies have reported measured noise levels aboard ships. This study aimed to describe the noise levels aboard vessels in the Royal Norwegian Navy (RNoN), and to assess the noise exposure of personnel aboard RNoN vessels. In 2012/2013 noise measurements were conducted aboard 14 RNoN vessels from four different vessel classes (frigates, coastal corvettes, mine vessels, and coast guard vessels) which were included in this study. Mean and median A-weighted noise levels (L p,A) in decibel (dB(A)) were calculated for different locations in each vessel class. The noise exposure of RNoN personnel was assessed by dosimeter measurements, and with a task-based (TB) strategy. The TB strategy used means of area measured noise levels in locations and the personnel's mean reported time spent in the respective locations to estimate the exposure. Area measurements of noise during sailing with typical operating modes, showed that for all vessel classes the noise levels were high in engine rooms with median L p,A ranging from 86.4 to 105.3 dB(A). In all the other locations the vessel class with the highest noise levels (coastal corvettes) had a median L p,A ranging from 71.7 to 95.0 dB(A), while the vessel class with the lowest noise levels (coast guard vessels) had a median L p,A ranging from 41.5 to 57.8 dB(A). For all vessel classes the engineers and electricians had amongst the highest 24-hour noise exposure (L p,A,24h), both before and after adjusting for estimated use of hearing protective devices (L p,A,24h > 67.3 dB(A)). The vessel class with the highest personnel exposure levels (coastal corvettes) had L p,A,24h ranging from 76.6 to 79.3 dB(A). The vessel class with the lowest personnel exposure levels (coast guard vessels) had an L p,A,24h ranging from 47.4 to 67.3 dB(A). In general, the dosimeter measurements gave higher exposure levels than those estimated with the TB strategy. All vessel classes, except the coast guard vessels, had noise levels exceeding the RNoN standard's recommended maximum noise levels. The area measured noise levels and the personnel's exposure estimates indicate that navy personnel aboard RNoN vessels are at risk of acquiring adverse health effects from exposure to noise, and that a program to reduce the noise levels should be implemented.

Contrast sensitivity and the effect of 60-hour sleep deprivation.

PURPOSE: The study aimed to evaluate the possible influence of prolonged sleep deprivation on achromatic and chromatic (red-green and blue-yellow) contrast sensitivity (CS). METHODS: During 60-hr sleep deprivation, CS was measured in 11 naval officers every sixth hour using videographic (Vigra-C) sine-wave-generated stimuli. RESULTS: When comparing the CS measurements obtained in the first and last 24 hr of the study, no statistically significant mean changes of achromatic CS (2.0, 5.9 and 11.8 cpd) or yellow-blue CS (0.6, 2.0 and 4.7 cpd) were found, while a significantly increased mean red-green CS at 2.0 and 4.7 cpd was recorded in the last 24 hr (p = 0.003 in both). The variance of achromatic and chromatic CS measurements in the group did not differ significantly in the first and last 24 hr test periods. CONCLUSIONS: Prolonged sleep deprivation does apparently not cause clinically or occupationally significant changes of contrast sensitivity in otherwise healthy subjects with normal visual acuity.

Hearing loss in the royal Norwegian Navy: a cross-sectional study.

OBJECTIVES: Prior studies have indicated a high prevalence of noise-induced hearing loss (NIHL) among Navy personnel; however, it is not clear whether this is caused by work on board. The present study aimed to assess the prevalence of hearing loss among Navy personnel in the Royal Norwegian Navy (RNoN), and to investigate whether there is an association between work on board RNoN vessels and occurrence of hearing loss. METHODS: Navy personnel currently working on board RNoN vessels were recruited to complete a questionnaire on noise exposure and health followed by pure tone audiometry. Hearing loss was defined as hearing threshold levels ≥25 dB in either ear at the frequencies 3,000, 4,000 or 6,000 Hz. Hearing thresholds were adjusted for age and gender using ISO 7029. RESULTS: The prevalence of hearing loss among Navy personnel was 31.4 %. The work exposure variables: years of work in the Navy, years on vessel(s) in the Navy and years of sailing in the Navy were associated with reduced hearing after adjusting for age, gender and otitis as an adult. Among the work exposure variables, years of sailing in the Navy was the strongest predictor of reduced hearing, and significantly reduced hearing was found at the frequencies 1,000, 3,000 and 4,000 Hz. CONCLUSIONS: Our results indicate that time spent on board vessels in the RNoN is a predictor of reduced hearing.

Contrast sensitivity measured by two different test methods in healthy, young adults with normal visual acuity.

PURPOSE: This study reports contrast sensitivity (CS) reference values obtained by two different test methods in a strictly selected population of healthy, young adults with normal uncorrected visual acuity. Based on these results, the index of contrast sensitivity (ICS) is calculated, aiming to establish ICS reference values for this population and to evaluate the possible usefulness of ICS as a tool to compare the degree of agreement between different CS test methods. METHODS: Military recruits with best eye uncorrected visual acuity 0.00 LogMAR or better, normal colour vision and age 18-25 years were included in a study to record contrast sensitivity using Optec 6500 (FACT) at spatial frequencies of 1.5, 3, 6, 12 and 18 cpd in photopic and mesopic light and CSV-1000E at spatial frequencies of 3, 6, 12 and 18 cpd in photopic light. Index of contrast sensitivity was calculated based on data from the three tests, and the Bland-Altman technique was used to analyse the agreement between ICS obtained by the different test methods. RESULTS: A total of 180 recruits were included. Contrast sensitivity frequency data for all tests were highly skewed with a marked ceiling effect for the photopic tests. The median ICS for Optec 6500 at 85 cd/m2 was -0.15 (95% percentile 0.45), compared with -0.00 (95% percentile 1.62) for Optec at 3 cd/m2 and 0.30 (95% percentile 1.20) FOR CSV-1000E. The mean difference between ICSFACT 85 and ICSCSV was -0.43 (95% CI -0.56 to -0.30, p<0.00) with limits of agreement (LoA) within -2.10 and 1.22. The regression line on the difference of average was near to zero (R2=0.03). CONCLUSION: The results provide reference CS and ICS values in a young, adult population with normal visual acuity. The agreement between the photopic tests indicated that they may be used interchangeably. There was little agreement between the mesopic and photopic tests. The mesopic test seemed best suited to differentiate between candidates and may therefore possibly be useful for medical selection purposes.

Mental readiness for maritime international operation: procedures developed by Norwegian navy.

Seafarer's mental health is vital for a well-functioning organisation. Neglecting mental health status on board could be extremely costly for both the crew affected as well as the company. The present article outlines an extensive programme implemented in the Royal Norwegian Navy for personnel deployed in international operations. The challenges involved in international operations bare similarities to onboard personnel in civilian maritime operations. The program utilised by the Royal Norwegian Navy is extensive and not immediately applicable to civilian maritime companies. However, elements of this program could be used with limited resources. Questionnaire based screening, before, during and at the end of a contract period could result in early detections of mental health problems and increased retaining of personnel. This should be done by health professionals. Early targeting of at risk personnel could prevent serious costs for the individual as well as the company.

Cause-specific mortality and cancer incidence among 28,300 Royal Norwegian Navy servicemen followed for more than 50 years.

OBJECTIVES: The aim of this study was to examine mortality and cancer incidence in a cohort of 28,300 military servicemen known, from personnel files, to have served in the Royal Norwegian Navy during 1950-2004. METHODS: The cohort was followed from 1951-2007 for mortality and from 1953-2008 for cancer. Standardized mortality ratios (SMR) and incidence ratios (SIR) for cancer were calculated from national rates. Internal comparisons [rate ratios (RR)] were made using Poisson regression. RESULTS: Mortality for all Navy personnel was lower than expected for all causes combined (SMR 0.84) and for most disease groups and violent causes, but not for cancer mortality (SMR 1.02). Vessel crews had consistently higher SMR than land-based personnel, still with rates lower than - or close to - national ones. The relative risk between the two subgroups was in the same direction for mortality from alcohol abuse and non-malignant alcohol-related diseases (RR 1.56) and for the incidence of alcohol-related cancers (RR 1.58) and lung cancer (RR 1.65). An overall small excess in the incidence of all cancers combined for the entire cohort (SIR 1.06) was caused by prostate cancer, malignant melanoma, and non-melanoma skin cancer. An excess of bladder cancer was observed among submariners (SIR 1.53). CONCLUSION: The low all-cause mortality was in line with a "healthy soldier effect". Navy personnel had a lower-than-expected mortality from accidents and suicide. Alcohol-related diseases were more frequent among vessel crews than among land-based personnel, but largely comparable to the rates among all Norwegian men.

Improving the saccade peak velocity measurement for detecting fatigue.

The aim of the study was to compare saccadic peak velocity (SPV) values measured with video based Fitness Impairment Tester (FIT) and electro-oculography (EOG) during prolonged wakefulness. We tested different numbers of saccades and two saccade paradigms to improve the EOG measurements for detecting fatigue. The SPVs were measured from 11 fast patrol boat navigators with FIT and EOG every sixth hour until 54 h. Subjective sleepiness was assessed with the Karolinska Sleepiness Scale. EOG was measured using an overlap and a gap paradigm and the data was divided into sequential five 20-saccade blocks and cumulative blocks of 20, 40, 60, 80, and 100 saccades. Compared to the gap paradigm, the overlap paradigm produced a higher number of analyzable saccades for a given measurement time. The shorter measurements (20-40 saccades) appeared to be more sensitive for fatigue, whereas the longer measurements (60-100 saccades) were more sensitive to time spent on the task. Thus, the optimal number of saccades varies also depending on the research question. The EOG method was more sensitive to fatigue than FIT. The FIT values measured after 30 and 36 h of wakefulness did not differ significantly from the baseline values, while subjective sleepiness and the EOG values showed that the participants were significantly less alert at these time points. The EOG measurements can be improved for detecting fatigue by using the overlap saccade paradigm. The SPV values measured with the EOG method appear to be somewhat more sensitive in detecting fatigue than the FIT method.

Asbestos-related cancers among 28,300 military servicemen in the Royal Norwegian Navy.

INTRODUCTION: This study focus on the incidence of asbestos-related cancers among 28,300 officers and enlisted servicemen in the Royal Norwegian Navy. Until 1987, asbestos aboard the vessels potentially caused exposure to 11,500 crew members. METHODS: Standardized incidence ratios (SIR) were calculated for malignant mesothelioma, lung cancer, and laryngeal, pharyngeal, stomach, and colorectal cancers according to service aboard between 1950 and 1987 and in other Navy personnel. RESULTS: Increased risk of mesothelioma was seen among engine room crews, with SIRs of 6.23 (95% CI = 2.51-12.8) and 6.49 (95% CI = 2.11-15.1) for personnel who served less than 2 years and those with longer service, respectively. Lung cancer was nearly 20% higher than expected among both engine crews and non-engine crews. An excess of colorectal cancer bordering on statistical significance was seen among non-engine crews (SIR = 1.14; 95% CI = 0.98-1.32). Land-based personnel and personnel who served aboard after 1987 had lower lung cancer incidence than expected (SIR = 0.77; 95% CI = 0.64-0.92). No elevated risk of laryngeal, pharyngeal, or stomach cancers was seen. CONCLUSION: The overall increase (65%) in mesotheliomas among military Navy servicemen was confined to marine engine crews only. The mesothelioma incidence can be taken as an indicator of the presence or absence of asbestos exposure, but it offered no consistent explanation to the variation in incidence of other asbestos-related cancers.

Effects of 60 hours of total sleep deprivation on two methods of high-speed ship navigation.

This study investigated how workload and performance in high-speed ship navigation was affected by sleep deprivation using methods based on either paper charts or electronic chart display and information systems (ECDIS). In two separate weeks, five navigators sailed 10 routes in high-fidelity simulators while undergoing progressive sleep deprivation for up to 60 h. Results showed that navigation performance was better using ECDIS, but was largely unaffected by sleep deprivation in both. There was significant interaction between speed, sleep deprivation and navigation method, indicating that navigators using ECDIS reduced their speed more while sleepy. Secondary task performance was reduced by sleep deprivation, but was equally affected in both conditions. Workload was higher in the ECDIS condition, as indicated by subjective ratings and heart rate variability. No significant differences in sleepiness were found, but electroencephalographic recordings indicated more frequent microsleep episodes in the ECDIS condition. This may be influenced by lower overall arousal while navigating with ECDIS.

Effects of navigation method on workload and performance in simulated high-speed ship navigation.

This study examines mental workload and performance in simulated high-speed ship navigation. Two navigation methods were compared based on an electronic chart display and information system (ECDIS) and a conventional system using paper charts. Twenty naval cadets navigated in high-fidelity simulators through a 50 nautical mile course with varying levels of difficulty. Results showed that ECDIS navigation significantly improved course-keeping performance, but reduced the total amount of communication on the bridge. No differences were observed in subjective workload between groups. Heart rate variability and skin conductance measurements indicated higher workload in conventional navigation, but the differences between groups were not significant.

Establishment of the Royal Norwegian Navy personnel cohorts for cancer incidence and mortality studies.

INTRODUCTION: Media focus on health problems among personnel in the Royal Norwegian Navy spurred a broad scale investigation, including cancer incidence and mortality studies. The studies were planned as historical prospective cohort studies. METHODS: Cohorts of military and civilian personnel serving in the Navy during 1950 to 2005 were established by manually entering paper-based service history files into the data system at the Headquarters Defence Command Norway. The files were collected from Headquarters Defence Command Norway, the naval bases, and the National Archives of Norway. RESULTS: The military cohort consists of 29,056 officers and enlisted personnel (2.5% women) with an average of 6 years of service in the Navy. Year of birth spans 1883 to 1985; the median is 1954. The cohort of 8,378 civilians (39% women) has an average of 11 years in the Navy; the year of birth spans 1884 to 1988 with a median of 1942. Both cohorts are regarded as virtually complete.

A survey of occupational health in the Royal Norvegian Navy.

OBJECTIVE: The aim of this article is to describe possible risk factors in the work environment that can affect the health of staff of the Royal Norwegian Navy (RNoN). The article presents the main results from a subproject related to a major surveillance of the health and work environment in this population. The project was performed as a response to general concerns regarding harmful work environment and negative health effects for these employees. PARTICIPANTS AND METHODS: In 2002, a questionnaire was sent out to all the employees in RNoN, and they answered during a period of three months. The overall response rate was 58% (n=2265), 2001 men and 250 women (14 unknown sex). 1581 military employees and 580 civilians participated (104 unknown). Mean age was 38 (range 18-70). Questions about years at work, exposure to chemical, physical and ergonomic hazards were developed for this particular study. Questions about allergy, asthma, hand eczema, hearing loss, cardiovascular disease, diabetes mellitus and cancer were asked. Musculoskeletal disorders were obtained by a standardized instrument. RESULTS: Exposure to noise, heavy lifting, twisted work positions and work close to antennas and communication equipment occurred often in this population. The most commonly reported diseases that might be work related were hand eczema, hearing loss and low back pain. CONCLUSIONS: The results indicate the presence of several possible risk factors to health related to the work environment in this population. The project gives a basis for further action regarding the Health Safety and Environment work within RNoN.