The impact of vision on road safety and evidence surrounding lenses that protect patients from blue light were just two of several fascinating topics addressed by speakers at the annual Specsavers Dispensing Conferences, held in major cities of Australia during August.
The conference was opened by Richard Couch, Specsavers’ Head of Dispensing Advancement, who said “dispensing and optical dispensers play a core and critical role in the delivery of eye care services”.
ROAD SAFETY AND VISION
Prof. Joanne Wood, School of Optometry & Vision Science, Queensland University of Technology, spoke extensively about eye conditions that significantly impact drivers’ vision and increase the incidence of injury.
She said current vision tests for driver licence renewal only include visual acuity (VA) and visual fields – yet VA has not been shown to be a very strong predictor of crash risk. Prof. Wood said contrast sensitivity, useful field of view and motion sensitivity were much more valuable as studies have shown these significantly impact driving performance and safety. Additionally, she said patient self-reporting on their driving performance was not a reliable indicator, primarily because people do not notice gradual deterioration associated with disease such as cataract, glaucoma and age related macular degeneration (AMD). She said many are unlikely to self-report their deteriorating vision until the late stages of eye disease. For example, she said studies had shown people with cataracts experienced contrast and glare sensitivity – particularly when driving at night – and were 2.5 times more likely to have a crash than controls. Despite this, around a quarter of people with cataracts continue to drive while not meeting the vision standards required to hold a driving licence.
Drivers with glaucoma were 3.6 times more likely to be involved in an injurious crash, and risks increased with more severe visual field loss. Observing pedestrians, street signs, approaching major intersections, and lane keeping, were most problematic for people with glaucoma.
Similarly, people with intermediate AMD were observed to have problems with maintaining lane position, and observing street signs and pedestrians. Prof. Wood said people with intermediate AMD reported reducing their driving exposure and avoided driving in challenging conditions.
In general, the crash risk for older drivers (over 70) is equivalent to that of teenagers, however there are social implications associated with cessation of driving among older people – they are at risk of losing independence, isolation and depression. While older people should be encouraged to continue to drive, eye health professionals should remind older patients of the need to wear prescribed spectacles and avoid driving in challenging conditions.
Prof. Wood spoke about challenging road conditions, such as glare, night-time, rain and fog and the impact contact lenses can have on these conditions. She said well-fitted contact lenses can improve vision on the road however dispensers must be aware of the way different contact lenses impact mesopic sensitivity, which in turn can affect driving performance.
She cited studies which have shown that for patients with low levels of astigmatism, toric lenses led to better driving performance than spherical lenses; and rigid gas permeable lenses may cause flares and haloes if the back optical zone diameter is less than the mesopic pupil diameter. Additionally, she said progressive lenses for presbyopes may alter head and eye movement tracking and saccades, which again can impact driving performance.
BLUE LIGHT DAMAGE QUESTIONED
Emeritus Professor Stephen Dain, from the University of New South Wales, spoke on the controversial topic of blue light, citing his own research and analysis of epidemiological data. Prof. Dain explained that although it has been known that blue light can damage the retina since at least 1971, what has been unclear is whether extremely low levels of blue light over a very long period can cause damage.
“Whenever there is damage in the eye there is always a repair mechanism – the photoreceptors are being damaged and repaired all the time, and it’s only when the damage overwhelms the repair mechanism that we get problems,” he said.
Prof. Dain noted that the eye’s crystalline lens absorbs “a fair degree of UVA” and as we age, the lens yellows and its level of protection against UVA and blue light increases.
His analysis of epidemiological evidence led him to the conclusion that there is evidence of a link between very high levels of sunlight (greater than eight hours per day) and neovascular macular degeneration, but no clear evidence of a link between exposure to sunlight and early AMD, and in fact the Blue Mountains study showed moderate levels of sunlight exposure are protective of AMD.
Additionally, he said there is some evidence to suggest that short wavelengths may be useful to younger eyes. “For instance, there is some evidence that blue light is protective against myopia and red light is protective against hyperopia,” said Prof. Dain.
“Evidence is clear that the levels of blue light outdoors are far higher than those from indoor light (eg. LEDS, halogen lights, plasms screens, digital devices etc), however, the cumulative effect of a moderate outdoor lifestyle is not proven to damage the retina… the only proven hazard is looking directly at the sun, which you would need to do for eight seconds before causing any damage to the retina.”
Prof. Dain’s comparison of different light sources (LED, halogens, fluorescents, plasma TV, OLED TV, and computer screens etc) found no significant difference in the blue light emitted from any of the technologies when set at the same brightness and correlated colour temperatures. “The correlated colour temperature (blueness/yellowness) is what determines the blue content, not the technology. So the zero cost option to reduce the blue light dose, if it really bothers you, is to set the screen with the lowest correlated colour temperature and reduce the screen brightness.”
Additionally if a person is still concerned about the idea that the retina might be damaged by LED lights, they should select a warm white LED. “Indoor light levels are far lower than those outdoors in absolute terms… In the worst case scenario, a person would need 243 days of continuous viewing of the brightest computer screen found to reach occupational safety limits.”
Prof. Dain said, “the risks for AMD remain genetics, age, aphakia, smoking and diet, and advice to patients should concentrate on the last two. Where a person’s occupation is largely outside, wraparound sunglasses are a wise choice for a number of reasons.”
