Sunday, June 22, 2014

Seniors driving at night- the impact of age and visual abilities

Age and driving at night
A new study appeared in the journal Ophthalmic & Physiological Optics that has implications for the safety of both older drivers and pedestrians.  It also highlights the inadequacies of current legal definitions of who is safe to drive.  Those rules only account for visual acuity and not measures of real-world visual processing such as processing speed or useful field of view.

The researchers who authored the study sought to investigate the effects of driver age on the ability of the drivers to notice pedestrians at night and to determine and which aspects of visual performance can predict a driver's ability to recognize pedestrians at night. The researchers took two groups of drivers: a group of visually normal drivers around the age of 24 and another group of drivers around the age of 72.

The researchers then measured the visual performance of drivers in a laboratory-based testing session.  The parameters measured were visual acuity, contrast sensitivity, motion sensitivity and the useful field of view. Then the researchers recorded the distances at which drivers noticed pedestrians at night while the drivers drove along a closed road coarse.

The pedestrians walked in place, sideways to the oncoming vehicles.  Some of them wore a standard high visibility reflective vest.  Others wore reflective tape positioned on the movable joints such as shoulders, elbows, wrists, waist, knees and ankle.  The latter is known as "biological motion". 

The results of the study were that the biological motion reflective strips made pedestrians easier to recognize when compared to the reflective vests and that older drivers had a significantly harder time noticing pedestrians compared to younger drivers:

driver age and pedestrian clothing significantly affected the distance at which the drivers first responded to the pedestrians. Older drivers recognised pedestrians at approximately half the distance of the younger drivers and pedestrians were recognised more often and at longer distances when they wore a biological motion reflective clothing configuration than when they wore a reflective vest. Motion sensitivity was an independent predictor of pedestrian recognition distance, even when controlling for driver age. 
The night-time pedestrian recognition capacity of older drivers was significantly worse than that of younger drivers. The distance at which drivers first recognized pedestrians at night was best predicted by a test of motion sensitivity.  

These findings may ultimately lead to new rules on the assessment of driver safety.  Unfortunately, this is not likely to happen soon because other tests that have been shown to correlate to safe driving, such as contrast sensitivity function, and Useful Field of View are still not a part of any state-mandated driver tests.  Even so, it is important for eye doctors to be aware of this information to properly counsel their older patients, who often come to them with complaints about feeling unsafe while driving. 

The study's results also suggest that for pedestrians to be safe at night, they should wear reflective strips at their movable joints to make themselves most noticeable to older drivers.

Ophthalmic & Physiological Optics: The Journal of the British College of Ophthalmic Opticians (Optometrists)
Seeing Pedestrians at Night: Effect of Driver Age and Visual Abilities Ophthalmic Physiol Opt 2014 Jun 02;[EPub Ahead of Print], JM Wood, P Lacherez, RA Tyrrell

Tuesday, May 13, 2014

Lighting needs for quality vision in ageing eyes

light needs and the ageing eyes of seniors
An important part of caring for the vision needs of older adults is paying attention to lighting.  An older eye needs three times more light than a younger eye.   For example, if a 19 year-old needs a 60 watt light bulb, a 60 year-old needs 180 watts of light.  I'm not even sure that a light bulb that powerful is commonly available.  And as we age, we need even more light.  An 80 year old person may need 300 watts of light.

Older adults need more light because the amount of light that reaches the retina at the back of their eyes is only one quarter of what it is for younger eyes.  That's why it is critical to emphasize the use of proper lighting.  As people age, few of them adjust the lighting in their homes, having often lived in the same home for decades.  The home and the lighting within it remains the same as the occupants age and require more light for quality vision.

Lighting is often the reason why low vision patients do very well in the office with controlled conditions and optimal lighting.  When they get home with their new low vision device, they can't read as well as they did in the clinic.  The reason is often poor lighting in their home environment. In fact, with some older patients, their vision will improve more with better lighting than with new glasses.
Anti-reflective of glare free lenses let in more light and are recommended for older patients.
Glare is eliminated by anti-reflective lenses, which allow more light to pass through the lens and into the eyes of older adults.  This means that more light will reach the retina at the back of their eyes.  With older adults already being light deficient compared to younger people, they need as much light as they can get.

However, glasses can make a difference.  Anti-reflective lenses are a must for older eye.  More light passes through an anti-reflective lens than a regular lens, that means more light will reach the retinal of the older eye, resulting in better quality vision.

Monday, March 24, 2014

Loss of depth perception in older adults

Depth perception in elderly adults
One often overlooked aspect of vision loss that many adults experience as they age is loss of depth perception. Older adults are 10 times more likely to lose depth perception and be at increased risk of falls and the often serious injuries that result. Early detection and treatment are key to reducing the risk of serious injuries.

A new study published in the journal, Optometry & Vision Science, examined one cause of depth perception loss: anisometropia.  The study has confirmed what we already know from working with with elderly patients in our Vancouver optometry clinic: changes in the eyes as we age can degrade our ability to see depth (stereopsis) and in three dimensions (3D vision).

One famous example of a case of depth perception loss and successful treatment using optometric vision therapy rehabilitation is the case of the father of neuroscientist Susan Barry, which you can read about here.

Related article:

When seniors loose depth perception and need to see a developmental optometrist
Thursday, June 28, 2012

Saturday, December 14, 2013

Low Vision and Blindness Rehabilitation in Vancouver

Vancouver Low vision and blindness rehabilitation

This article hopes to describe what we do at our Vancouver eye clinic when we provide rehabilitation services to people with low vision.

The basic goals of vision rehabilitation is to maximize functional independence, to improve quality of life, and to help the patient adapt to the psycho-social aspects of vision loss. Before and during rehabilitation, we evaluate and treat the patient's existing medical eye condition using standard techniques with the goal of maximizing or maintaining the patient's vision.  

Vision rehabilitation trains patients to use their remaining vision (or other ways to compensate for lost vision) to make practical and effective adaptations in their behavior and their environment to facilitate activities of daily living, ensure safety, and maintain independence.

Rehabilitation is individualized to the particular patient.  It is tailored to the patient’s goals, limitations, and resources (e.g. availability of transportation, finances, and caregivers). Some patients even have other physical limitations that impact the design of the individual rehabilitation program.  For example, hearing, mobility, and neurological problems can prevent or make it difficult for the patient to use some standard devices and to undertake some types of rehabilitation. A proper rehabilitation effort will take these limitations into account and work around them or through them.

There are certain things that we want a patient to get our of their rehabilitation program and they include the following:

§  Improved understanding of emotional and psychological adjustments to vision loss.
§  Improved ability to independently complete the activities of daily living.
§  Improved knowledge and effective use of devices that can improve their quality of life and other resources that are available to them.

Vision rehabilitation has economic benefits. It is widely accepted that vision rehabilitation can drastically reduce the costs associated with injuries (for example, falls resulting in broken bones, brain injury, hip fractures, etc.) that are associated with vision loss as well as the loss of independence that accompanies vision loss. Vision rehabilitation can also prolong the productivity by people who are able to stay active in the community and even continue working despite vision loss.

Vision rehabilitation also has social benefits. Vision rehabilitation has been known to have significant positive effects on seniors' physical and mental health and the well-being of their families. There is literature supporting the positive effects of vision rehabilitation on function, social and pychological well-being, as well as quality of life generally (see Horowitz, A. The prevalence and consequences of vision impairment in later life. Top Geriatr Rehabil. 2004;20:185-195.).

Saturday, December 7, 2013

What is low vision?

Vancouver optometrist on what is low vision

Low vision is a level of vision impairment where the person is not totally blind but vision is less than normal. People with low vision are best helped using rehabilitation techniques that maximize the vision that remains. This is most often accomplished with low vision devices such as large print, magnifiers, and illumination.

Low vision may result from a variety of different ophthalmologic and neurological disorders and low vision is an impairment that may interfere with a person’s ability to carry out daily living and leisure activities, as well as the ability to work and earn a living at their chosen profession. Therefore, the ability to maximize visual function can restore some quality of life and the social, psychological and economic benefits that come with it.

Generally, low vision describes any condition of reduced vision that cannot be fixed by standard glasses, contact lenses, medication or surgery that disrupts a person’s ability to perform common age-appropriate visual tasks.

Low vision is best addressed through a low vision rehabilitation program designed by a doctor who assesses a patient's visual abilities and designs a training program to maximize the vision that remains or to maximize the patient's use of the healthy part of his or her eyes.  This may involve the use of technology, low vision devices, behaviour and environment assessments and more.

Wednesday, October 16, 2013

When should a patient come in for low vision rehabilitation?

Sometimes there are visual acuity guidelines for various activities like driving.  However, there are no such guidelines that suggest that a certain level of visual impairment is necessary before a patient should seek low vision rehabilitation.  Nevertheless, it is critically important that patients not be preselected for a referral to a low vision doctor. Some professionals believe that a patient is too old to benefit from low vision rehabilitation.  That attitude fails to show respect for the patient's own values and desire for his or her own quality of life.  

At patient should be referred for low vision rehabilitation on the basis of the patient's own complaints about their vision and if those complaints cannot be resolved with conventional eyeglasses, contact lenses or medical treatments.  The patient can then decide for his or her self whether the available rehabilitation approaches are suitable for and meet the patient's needs.