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ORIGINAL ARTICLE
Year : 2022 | Volume
: 26
| Issue : 4 | Page : 251-254
Effect of full-face and half-face helmet on functional vision and visual reaction time
Farhatbee N Kazi, Hiral Korani, Prema Chande
Department of Optometry, Lotus College of Optometry, Mumbai, Maharashtra, India
Correspondence Address:
Ms. Farhatbee N Kazi
709/A Noor Manzil, Al-aman Soc, Filter Pada, Powai, Mumbai, Maharashtra
India
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/ijoem.ijoem_459_20
Background: Motorcycle helmets are one of the most important protective gears in the automotive industry. However, some riders think they hinder their vision, which leads to helmet non-compliance.Hence, thorough research is required to evaluate the same. Aim and Objective: To assess the effect of full-face and half-face helmets on functional vision and visual reaction time (VRT). Setting and Study Design: Comparative experimental crossover study. Methods: The subjects aged between 18 and 35 years and who gave written consent to participate were included. Functional vision and VRT were assessed with and without the helmets. Helmets tested included a full-face helmet and a half-face helmet. Results: A total of 52 subjects aged 20 ± 1.5 years, participated in the study. Of those, 16 were males and 36 were females. The mean stereopsis without any helmet was 44.42 ± 6.3 arcs of second that reduced to 60.57 ± 13.34 arcs of second with a full-face helmet and to 60.38 ± 14.27 arcs of second with a half-face helmet. Repeated-measure analysis of variance showed a significant reduction in stereopsis in both types of helmets (P < 0.05) as compared to without a helmet. However, contrast sensitivity, VRT, and visual field did not show any significant difference (p > 0.05) when compared to the baseline or within the helmet types. Conclusion: The visor significantly affects the stereopsis while viewing through it. The study did not find the exact cause of this reduction, and hence, further evaluation is recommended.
Keywords: Full-face helmet, half-face helmet, helmets, visual function, visual reaction time, stereopsis
Helmets are one of the most important protective gears in the automotive industry. According to the Indian National Centre for Statistics and Analysis of the National Highway Traffic Safety Administration, helmets are powerful in avoiding fatalities by 37%.[1] According to the provisions of section 129 MVA'88 of the Indian Penal Court, protective helmets are required to match the standards of the Bureau of Indian Standards.[2] These standards include minimum impact and penetration capabilities, chin strap retention qualities, and a prescribed minimum field of view.[1] According to a recent investigation of helmet use behavior of motorcyclists and the effectiveness of enforcement campaigns, more than 50% of individuals agreed to have hearing and vision problems with helmets and think that their design needs to be improved.[3]
Helmets can be broadly classified into two segments, that is, full-face helmets and half-face helmets. Full-face helmets offer facial protection in addition to impact protection. Their main feature is a chin bar that extends outward, wrapping around the chin and jaw area. Extending above the jaw, there is a vision port (the open space for viewing) that allows the wearer a maximum range of sight, in line with the requirements for peripheral (210° of visual field) and vertical (102° of visual field) vision.[4] Half-face helmets give standard protection from impact with their hard-outer shell and crushable inner liner, but compared to the full-face type, they offer only limited protection for the jaw and chin area. They may or may not have retractable visors to protect the eyes.[4] The requirements for the peripheral and vertical visual fields are the same for any helmet.
While providing the required protection, the helmets should not hamper the vision of the wearer by creating any distortion. The spherical, cylindrical, and prismatic error should not be more than 0.50 Diopter.[4] The functional visual aspects include but are not limited to the field of view, contrast sensitivity, visual acuity, color vision, and stereopsis. Naturally, the field of view with a helmet is lesser in most directions as compared to those without it.[2] The field of view and use of helmets have received fair attention in the scientific literature.[5] McKnight et al.[6] analyzed data for the actual causes of road accidents and concluded that 11% of the accidents were related to the rider's field of view. In recent times, Joshi et al.[2] fo und that the peripheral field of vision is significantly reduced beyond the set standard in right temporal, left temporal, and upward and downward directions by the use of standard helmets, suggesting scope for a newer helmet design with minimal field restrictions.
Materials and MethodsA crossover study was carried out after approval from the institutional review board. Subjects between the ages of 18–35 years were included in the study. All volunteers provided written informed consent before enrolling in the study. The procedures followed the Declaration of Helsinki guidelines. A preliminary examination was done to exclude individuals with any ocular pathology such as glaucoma, cataract, binocular abnormalities, high myopia, high hyperopia, pre-existing visual field defects, color vision defects, binocular anomalies, poor stereopsis, or any history of ocular trauma or surgery. Undilated ophthalmoscopy, refraction, cover test, and slit-lamp examination were done to rule out the same.
Two types of helmets were used in the study, full-face and half-face helmets. For baseline evaluation, visual function assessment was first carried out and recorded without the helmets. The subjects were randomly assigned to any one type of helmet group to be tested first. The visual function tests were then performed with a randomly assigned helmet group. The group was then crossed over to complete the tests with the other helmet too. All tests were performed on the same day. Also, care was taken to eliminate memory bias by randomizing the test order.
Functional vision assessment
The functional vision assessment included the testing for stereopsis, contrast sensitivity, contrast sensitivity with glare, visual reaction time (VRT), distance and near visual acuity measurement at high contrast, and peripheral visual field assessment. The methods for each of these are specified below;
Stereopsis: It is the perception of depth created by the superimposition of images from both the eyes or appreciation of 3-dimensional structures based on visual information by individuals with normally developed binocular vision. Titmus Stereo Fly test (Stereo Optical Co. Essilor, Illinois, USA) was used to assess stereopsis. The subjects were asked to perform the test by wearing polaroid glasses over their correction (if any) and then wearing a helmet above it with visors on.
Contrast sensitivity: Contrast sensitivity measures the ability to appreciate differences in finer shades of light. A CSV 1000LV (David W. Evans, Vector Vision, Ohio, USA) contrast sensitivity chart was used for this assessment. The patient was asked to identify the alphabets on each row. Testing began with the left grating in row A. At a time, a single row was illuminated. The lowest contrast level (i.e., the last alphabet) in which the patient can correctly identify the alphabets was considered the contrast sensitivity of that eye. For gaining a score, the patient must recognize at least two of the three triplets of the same contrast. The procedure is done in dim light.[7] Contrast sensitivity was recorded in percentage.
Contrast sensitivity with glare: It was done on a CSV 1000LV chart (David W. Evans, Vector Vision, Ohio, USA). The procedure was the same as contrast sensitivity measurement, except that, here, the glaring light was turned on. It was reflected from both sides of the head and was calibrated to mimic car headlights. The inbuilt glare light produced a luminance of 85 cd/m2 for standard testing.[7]
Visual reaction time: It is the time required to respond to a visual stimulus. It was assessed using a psychology experiment building language v2.1 software by Mueller at the Michigan Technological University, USA.[8] The subjects had undergone a test called “simple response time,” where they had to press the “X” button on the keyboard as soon as it appeared on the screen. Each subject had to complete three sets of the test. All responses were automatically recorded by the software that provides the mean average value.
Peripheral visual field: It corresponds to the entire area that can be seen when the eye is directed forward. A tangent screen (Bjerrum Screen, Copenhagen, Denmark) was used to assess the subject's peripheral visual field monocularly (i.e., one eye was occluded with a patch) as it was easy to perform, less time-consuming, and was possible to perform while wearing helmets, which is not the case with the standard Humphrey visual field analyzer.[7] All data were mapped on the recording sheet and then compared with the baseline data collected without any helmet and analyzed further.
Statistical analysis
Statistical analysis was done using the IBM Statistical Package for Social Sciences v23.0. The Shapiro–Wilk test was performed to check the normality. Repeated-measure analysis of variance (RMANOVA) comparing means of multiple variables was performed to check the significance. With a confidence interval of 95% and a level of significance (P-value) of 0.05. All P values were produced after posthoc pairwise comparison using Bonferroni correction.
ResultsThe study included 52 subjects with 16 (30%) males and 36 (70%) females aged between 18 and 35 years and a mean age of 20 years ± 3 years.
Stereopsis: A decrease in mean stereopsis with the full-face and half-face helmets as compared to the baseline was observed, and this reduction was statistically significant (P = 0.000) [Table 1].
Table 1: Univariate analysis of functional vision assessment at baseline/without helmet and with full-face and half-face helmetsContrast sensitivity: Contrast sensitivity (with and without glare) was not found to be affected significantly across the three conditions (P = 0.149 and 0.75). RMANOVA showed a decrease in mean contrast sensitivity with and without glare (−0.238 and −0.085, respectively), but it was not statistically significant (P = 0.164 and 1.00) [Table 1].
Visual reaction time: The VRT was not found to be significantly different across the three conditions (P = 0.956). Posthoc pairwise comparison using the Bonferroni correction also did not show any difference across the three groups [Table 1].
Visual field: Visual fields did not show any significant difference at 90, 180, 45, or 135° with or without either type of helmet (P = 0.239, 0.435, 0.180, and 0.513, respectively). Posthoc pairwise comparison also did not show any difference across the three groups [Table 1].
DiscussionPerception of surroundings in three dimensions is essential for judging the distance in motion and for a safe riding experience.[9] In this study, we found that depth perception was reduced with both types of helmets. However, the exact cause of such reduction is yet to be identified. According to Lovasik et al.,[10] depth perception can decrease in a curvilinear manner in aniseikonia and anisometropic conditions. If we take the curvature of the visor into account, we can assume that it may produce some level of aniseikonia which produces different image sizes in both eyes and hence decreases the stereopsis. Another reason for the presence of such aniseikonia could be unwanted astigmatism present on the visor surface due to an inefficient manufacturing process. If we assume that the curvature of the visor is the reason for the reduction in depth perception, it could be improved by making the visor flatter and placing it closer to the eye. Another solution could be replacing the visor with a pair of windproof goggles, whose surface could be treated with required anti-reflective coating, scratch-resistant coating, and hydrophobic coating, and prescribing powers would also be possible. However, these solutions require adequate research to prove their efficiency and can be a permanent replacement for conventional helmet visors.
A motorcycle rider has to adapt to changing contrast levels throughout the day, and they need to distinguish various road obstacles in different contrast levels. In this study, the contrast sensitivity was found to be reduced with both types of helmets. Although the reduction was not statistically significant, any such reduction in contrast sensitivity violates the ISI standards for helmet visors.[4] The helmets used in this research were new and free of scratches and abrasions. Hence, such reduction in contrast sensitivity could either be associated with the optical quality of the visor or the material used in the manufacturing of such visors, or both.
A study conducted by Joshi et al.[2] reported no delay in the visual reaction with any type of helmets they tested. Another similar study by Abbupillai et al.[5] found that the VRT was not affected in any healthy female and male helmet users.
In one of the previous studies, it has been found that on all subjects, the visual field when tested using Lister's perimeter was reduced significantly in all four gazes with both types of helmets. The field of vision downward and upward was more significantly reduced.[2] However, in this study, the visual field remained unaffected. The differences could be attributed to the differences in the measurement techniques used between our study and the previous study.
There were few limitations in the study such as all tests were conducted under static conditions; however, a dynamic testing environment with a large sample size may give a better understanding of the effect of a helmet on visual functions and the causes of such effects.
ConclusionBoth full-face and half-face helmets significantly affect the stereopsis and contrast sensitivity with and without glare. However, they do not affect the VRT and visual field significantly. Further research is necessary to measure the optical properties and the curvature of the visor to determine its fitness to be included in helmets.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Lotus College of Optometry.
Conflicts of interest
There are no conflicts of interest.
References
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