Comparing spectacle and toric contact lens prescribing trends for astigmatism

Background: The purpose of this study is to investigate and compare spectacle and contact lens (CL) prescription trends, with an emphasis on astigmatic refractive error prescribing differences for patients who purchase spectacles or CLs in South Korea. Methods: A retrospective study of patient records of a major optical chain in South Korea was conducted. De-identified data of age, gender, power of prescribed spectacles and/or CLs were extracted from the practice database. Inclusion criteria were being within the first 10,000 purchasers of spectacles or CLs or both. Results: The first 10,000 purchases comprised spectacles (59%) and CLs (41%) (male:female ratio 4:6). The proportion of purchasers who were female was significantly higher for CLs (88% female, 12% male) than spectacles (43% female, 57% male) (χ2=4480.36, df=1, P&lt;0.0001). There was a significant difference in the proportions of purchases by age group for spectacles and CLs (χ2=3246.69, df=3, P&lt;0.0001). Spherical power distribution of prescribed lenses was similar between the groups; however, cylinder power and axis were significantly different (P&lt;0.0001). CL astigmatic powers were more likely to be 1.00 DC or greater, whereas the majority of spectacle lenses had astigmatic power of 0.75 DC or less. In total, 90% of toric CLs were prescribed ×180 and 9% other meridians, unlike spectacles where 50% were prescribed ×180, 14% ×90 and 40% at oblique meridians. Conclusion: There is scope for providing increased toric lens correction amongst CL wearers and increasing the proportion of wearers who are male. The estimated gap for toric lens prescription amongst CL wearers who have clinically significant astigmatism ≥0.75 DC is about 59%.</p

Fractal Dimension Analysis of Transient Visual Evoked Potentials: Optimisation and Applications

Purpose The visual evoked potential (VEP) provides a time series signal response to an external visual stimulus at the location of the visual cortex. The major VEP signal components, peak latency and amplitude, may be affected by disease processes. Additionally, the VEP contains fine detailed and non-periodic structure, of presently unclear relevance to normal function, which may be quantified using the fractal dimension. The purpose of this study is to provide a systematic investigation of the key parameters in the measurement of the fractal dimension of VEPs, to develop an optimal analysis protocol for application. Methods VEP time series were mathematically transformed using delay time, τ, and embedding dimension, m, parameters. The fractal dimension of the transformed data was obtained from a scaling analysis based on straight line fits to the numbers of pairs of points with separation less than r versus log(r) in the transformed space. Optimal τ, m, and scaling analysis were obtained by comparing the consistency of results using different sampling frequencies. The optimised method was then piloted on samples of normal and abnormal VEPs. Results Consistent fractal dimension estimates were obtained using τ = 4 ms, designating the fractal dimension = D2 of the time series based on embedding dimension m = 7 (for 3606 Hz and 5000 Hz), m = 6 (for 1803 Hz) and m = 5 (for 1000Hz), and estimating D2 for each embedding dimension as the steepest slope of the linear scaling region in the plot of log(C(r)) vs log(r) provided the scaling region occurred within the middle third of the plot. Piloting revealed that fractal dimensions were higher from the sampled abnormal than normal achromatic VEPs in adults (p = 0.02). Variances of fractal dimension were higher from the abnormal than normal chromatic VEPs in children (p = 0.01). Conclusions A useful analysis protocol to assess the fractal dimension of transformed VEPs has been developed

The impact of presbyopic spectacles and contact lenses on driving performance

Presbyopia affects individuals from the age of 45 years onwards, resulting in difficulty in accurately focusing on near objects. There are many optical corrections available including spectacles or contact lenses that are designed to enable presbyopes to see clearly at both far and near distances. However, presbyopic vision corrections also disturb aspects of visual function under certain circumstances. The impact of these changes on activities of daily living such as driving are, however, poorly understood. Therefore, the aim of this study was to determine which aspects of driving performance might be affected by wearing different types of presbyopic vision corrections. In order to achieve this aim, three experiments were undertaken. The first experiment involved administration of a questionnaire to compare the subjective driving difficulties experienced when wearing a range of common presbyopic contact lens and spectacle corrections. The questionnaire was developed and piloted, and included a series of items regarding difficulties experienced while driving under day and night-time conditions. Two hundred and fifty five presbyopic patients responded to the questionnaire and were categorised into five groups, including those wearing no vision correction for driving (n = 50), bifocal spectacles (BIF, n = 54), progressive addition lenses spectacles (PAL, n = 50), monovision (MV, n = 53) and multifocal contact lenses (MTF CL, n = 48). Overall, ratings of satisfaction during daytime driving were relatively high for all correction types. However, MV and MTF CL wearers were significantly less satisfied with aspects of their vision during night-time than daytime driving, particularly with regard to disturbances from glare and haloes. Progressive addition lens wearers noticed more distortion of peripheral vision, while BIF wearers reported more difficulties with tasks requiring changes in focus and those who wore no vision correction for driving reported problems with intermediate and near tasks. Overall, the mean level of satisfaction for daytime driving was quite high for all of the groups (over 80%), with the BIF wearers being the least satisfied with their vision for driving. Conversely, at night, MTF CL wearers expressed the least satisfaction. Research into eye and head movements has become increasingly of interest in driving research as it provides a means of understanding how the driver responds to visual stimuli in traffic. Previous studies have found that wearing PAL can affect eye and head movement performance resulting in slower eye movement velocities and longer times to stabilize the gaze for fixation. These changes in eye and head movement patterns may have implications for driving safety, given that the visual tasks for driving include a range of dynamic search tasks. Therefore, the second study was designed to investigate the influence of different presbyopic corrections on driving-related eye and head movements under standardized laboratory-based conditions. Twenty presbyopes (mean age: 56.1 ± 5.7 years) who had no experience of wearing presbyopic vision corrections, apart from single vision reading spectacles, were recruited. Each participant wore five different types of vision correction: single vision distance lenses (SV), PAL, BIF, MV and MTF CL. For each visual condition, participants were required to view videotape recordings of traffic scenes, track a reference vehicle and identify a series of peripherally presented targets while their eye and head movements were recorded using the faceLAB® eye and head tracking system. Digital numerical display panels were also included as near visual stimuli (simulating the visual displays of a vehicle speedometer and radio). The results demonstrated that the path length of eye movements while viewing and responding to driving-related traffic scenes was significantly longer when wearing BIF and PAL than MV and MTF CL. The path length of head movements was greater with SV, BIF and PAL than MV and MTF CL. Target recognition was less accurate when the near stimulus was located at eccentricities inferiorly and to the left, rather than directly below the primary position of gaze, regardless of vision correction type. The third experiment aimed to investigate the real world driving performance of presbyopes while wearing different vision corrections measured on a closed-road circuit at night-time. Eye movements were recorded using the ASL Mobile Eye, eye tracking system (as the faceLAB® system proved to be impractical for use outside of the laboratory). Eleven participants (mean age: 57.25 ± 5.78 years) were fitted with four types of prescribed vision corrections (SV, PAL, MV and MTF CL). The measures of driving performance on the closed-road circuit included distance to sign recognition, near target recognition, peripheral light-emitting-diode (LED) recognition, low contrast road hazards recognition and avoidance, recognition of all the road signs, time to complete the course, and driving behaviours such as braking, accelerating, and cornering. The results demonstrated that driving performance at night was most affected by MTF CL compared to PAL, resulting in shorter distances to read signs, slower driving speeds, and longer times spent fixating road signs. Monovision resulted in worse performance in the task of distance to read a signs compared to SV and PAL. The SV condition resulted in significantly more errors made in interpreting information from in-vehicle devices, despite spending longer time fixating on these devices. Progressive addition lenses were ranked as the most preferred vision correction, while MTF CL were the least preferred vision correction for night-time driving. This thesis addressed the research question of how presbyopic vision corrections affect driving performance and the results of the three experiments demonstrated that the different types of presbyopic vision corrections (e.g. BIF, PAL, MV and MTF CL) can affect driving performance in different ways. Distance-related driving tasks showed reduced performance with MV and MTF CL, while tasks which involved viewing in-vehicle devices were significantly hampered by wearing SV corrections. Wearing spectacles such as SV, BIF and PAL induced greater eye and head movements in the simulated driving condition, however this did not directly translate to impaired performance on the closed- road circuit tasks. These findings are important for understanding the influence of presbyopic vision corrections on vision under real world driving conditions. They will also assist the eye care practitioner to understand and convey to patients the potential driving difficulties associated with wearing certain types of presbyopic vision corrections and accordingly to support them in the process of matching patients to optical corrections which meet their visual needs

Seeing pedestrians at night: visual clutter does not mask biological motion

Although placing reflective markers on pedestrians’ major joints can make pedestrians more conspicuous to drivers at night, it has been suggested that this “biological motion” effect may be reduced when visual clutter is present. We tested whether extraneous points of light affected the ability of 12 younger and 12 older drivers to see pedestrians as they drove on a closed road at night. Pedestrians wore black clothing alone or with retroreflective markings in four different configurations. One pedestrian walked in place and was surrounded by clutter on half of the trials. Another was always surrounded by visual clutter but either walked in place or stood still. Clothing configuration, pedestrian motion, and driver age influenced conspicuity but clutter did not. The results confirm that even in the presence of visual clutter pedestrians wearing biological motion configurations are recognized more often and at greater distances than when they wear a reflective vest

Effect of Simulated Visual Impairment on Nighttime Driving Performance

Purpose. This study investigated the effects of simulated visual impairment on nighttime driving performance and pedestrian recognition under real-road conditions. Methods. Closed road nighttime driving performance was measured for 20 young visually normal participants (M = 27.5 +- 6.1 years) under three visual conditions: normal vision, simulated cataracts, and refractive blur that were incorporated in modified goggles. The visual acuity levels for the cataract and blur conditions were matched for each participant. Driving measures included sign recognition, avoidance of low contrast road hazards, time to complete the course, and lane keeping. Pedestrian recognition was measured for pedestrians wearing either black clothing or black clothing with retroreflective markings on the moveable joints to create the perception of biological motion (“biomotion”). Results. Simulated visual impairment significantly reduced participants’ ability to recognize road signs, avoid road hazards, and increased the time taken to complete the driving course (p 0.05); the effect was greatest for the cataract condition, even though the cataract and blur conditions were matched for visual acuity. Although visual impairment also significantly reduced the ability to recognize the pedestrian wearing black clothing, the pedestrian wearing “biomotion” was seen 80% of the time. Conclusions. Driving performance under nighttime conditions was significantly degraded by modest visual impairment; these effects were greatest for the cataract condition. Pedestrian recognition was greatly enhanced by marking limb joints in the pattern of biomotion, which was relatively robust to the effects of visual impairment

Simulated Visual Impairment Affects Night-Time Driving and Pedestrian Recognition

PURPOSE: To determine how simulated visual impairment impacts on night-time driving performance and pedestrian recognition measured under real road conditions. EXPERIMENTAL DESIGN: Night-time driving performance of 20 young normal participants (M=27.5 ± 6.1 yrs) was assessed on a closed road circuit for three different visual conditions. The visual conditions were mounted in modified goggles and contained simulated cataracts, refractive blur selected to match the visual acuity of the cataract condition and normal vision. All participants had binocular visual acuity greater than 6/12 (20/40) when wearing the goggles and satisfied the visual requirements for driving. Driving measures included road sign recognition, detection and avoidance of low contrast road hazards, lane-keeping and time to complete the course. Participants were also scored on recognition of pedestrians who wore either black clothing or retroreflective markings on either the torso or the limb-joints to create “biomotion.” RESULTS: Simulated visual impairment reduced night-time driving performance (p[[lt]]0.05); posthoc testing indicated that these differences were greatest for the cataract condition, even though the cataract and blur conditions were matched for visual acuity. While visual impairment significantly reduced the ability to recognise the darkly clad pedestrians, the pedestrians wearing “biomotion” were seen 80% of the time. CONCLUSIONS: These data confirm that driving performance under night-time conditions is significantly degraded by the effects of early visual impairment and that pedestrian recognition is greatly enhanced by marking limb-joints to create “biomotion” which was relatively resistant to the effects of visual impairment

Seeing Pedestrians at Night: The Benefits of Biological Motion are Robust to Clutter

Collisions between vehicles and pedestrians are more common at night and insufficient conspicuity has been implicated as a causal factor. Incorporating the phenomenon of biological motion - placing reflective markers on a pedestrians\u27 major joints has been shown to make pedestrians more conspicuous to drivers at night. However, most on-road tests have been conducted in scenarios relatively free of visual clutter. We tested whether the presence of extraneous points of light degrades drivers\u27 ability to detect pedestrians wearing reflectors in several different configurations. Twelve younger (21–34 years) and 12 older (61–78 years) volunteers drove an instrumented vehicle 12 laps around a 1.8 km closed-road circuit at night and pressed a button whenever they realized that a pedestrian was present. Two pedestrians were positioned on the road\u27s shoulder wearing either all black clothing or all black clothing with 663 cm2 of silver retroreflective markings in four different configurations. One pedestrian walked in place at a point that was, on half of the laps, surrounded by reflective cones and posts (clutter). To test the effects of pedestrian motion, the other pedestrian stood still during half the laps and walked in place during the other half and was always surrounded by clutter. Reflector configuration dramatically influenced conspicuity. Without reflective markers, or with a reflective vest, most pedestrians were never detected. When pedestrians wore reflectors on their ankles and wrists, however, younger and older drivers responded at a mean distance of 285 m and 141 m, respectively. Importantly, the presence of visual clutter did not significantly influence response distances (p.05). Pedestrian motion enhanced conspicuity, particularly for older drivers. These results confirm that the phenomenon of biological motion can dramatically enhance the nighttime conspicuity of pedestrians and indicate that this effect is robust to the presence of visual clutter

Refractive Blur Reduces Both Day and Night-Time Driving Performance and Alters Driver Gaze Patterns

Purpose: : To investigate the effect of different levels of refractive blur on real world driving performance and eye movements measured under day and night-time conditions.Methods: : Participants included 12 visually normal, young adults (mean age=25.6 ± 5.2 years) who drove an instrumented research vehicle around a 4 km closed road circuit with 4 different levels of binocular spherical refractive blur (0.00 D, +0.50 D, +1.00 D, +2.00 D). The subjects wore optimal sphero-cylinder correction and the additional blur conditions were mounted in modified full-field goggles. The order of testing the blur conditions was randomized. Driving performance was assessed separately under day and night-time conditions with measures including road signs recognized, sign recognition distance, hazard detection and avoidance, gap detection, lane-keeping, speed and time to complete the course. Driving eye movements were also recorded using an ASL Mobile Eye tracking system.Results: : Refractive blur and time of day had significant effects on driving performance (p\u3c0.05), such that increasing blur and night-time driving reduced performance on all driving tasks except gap judgment and lane keeping. There was also a significant interaction between blur and time of day (p\u3c0.05), where the effects of blur were exacerbated under night-time driving conditions. Post hoc testing indicated that all blur conditions were different to one another except for the number of hazards hit, where only the difference between +0.50 D blur and baseline 0.00 D failed to reach significance. Refractive blur also significantly increased the number of eye movement fixations and the duration of fixations on roadside signs while driving.Conclusions: : The effects of blur were greatest under night-time conditions, even for levels of refractive blur as low as +0.50 D. Drivers also spent more time looking at signs rather than scanning the road ahead when driving with blur. These findings imply that the correction of refractive errors is essential for safe driving

Perceptions of older people regarding their vision and incident causation

Purpose: It is widely known that visual impairment (VI) is a risk factor for falls, but patients or their eye care practitioners may not recognize other kinds of incidents as being problematic because of their vision. Consequently, older people with VI may have unmet needs for advice on how to carry out activities of daily living safely. Therefore, the purpose of this study was to understand whether older people with VI consider their vision as a causative factor of incidents they experience and their perceptions regarding the prevention of future incidents. If sample size permitted, a secondary aim was to evaluate whether quantitative findings supported their perceptions. Methods: The study design was a prospective cohort study evaluating injurious and damaging incidents and related near misses using open questions in a written 2-weekly large-print diary with active follow-up over 8 weeks in older people (960 years, n = 80) with and without VI. Baseline measures included habitual binocular visual acuity, contrast sensitivity, visual fields, 3-m walk test, and Short Form 12 physical and mental component scores. Participants' diary entries were coded. Factor analysis and binary logistic analysis were used to investigate whether baseline measures were predictive of incident occurrence. Risk and preventative factors identified were compared. Results: Participants perceived that their vision was implicated in bump and fall incidents. Quantitative analysis indicated that contrast sensitivity and fitness were significant predictors of incident occurrence. Six vision-related and five nonYvisionrelated causative factors were identified by participants as contributing factors. Participants frequently stated "don't know" when asked to identify solutions to prevent incident recurrence. Conclusions: Participants had unmet needs for advice in relation to incident prevention. It would be prudent for eye care practitioners to raise incident prevention in eye care consultations regardless of voiced patient concerns.</p