Normal Vision or Visual Acuity is usually defined as the ability to see letters that subtend an angle of 5 seconds of arc at 6 metres from a viewing distance of 6 metres. This is known as 6/6 vision. (the USA is one of the few countries that still uses imperial measures and the equivalent is taken to be 20 feet, hence 20/20 vision).
If the best vision a person can see (even with glasses) is a letter 10 times that size, then the vision is 6/60 (or 20/200). This level of vision without a loss of visual field would make the person eligible to be ‘legally blind’. Better levels of vision accompanied by visual field loss (eg ‘tunnel vision’) may still be considered as ‘legal blindness’.
From this definition, you will realise that most people who are legally blind still have some vision. In the year 2000 it was estimated that 30,000 Australians were legally blind. About 2% of these were children.
However, it is estimated that between 3.9% and 4.7% of Australians over 40 have some vision loss that cannot be corrected with spectacles. Around 345,000 adults aged 40 or over have vision loss to 6/12 (able to see a letter twice the size of someone with normal vision) or a visual field smaller than 20 degrees (for driving a visual field of 120 degrees horizontally is considered safe)
The main causes of visual impairment in developed countries are age-related macular degeneration, glaucoma, diabetic retinopathy and cataract. In developing countries and under-developed areas of developed countries other common causes include trachoma, onchocerciasis (river blindness) and xerophthalmia (Vitamin A deficiency).
Surprisingly, a study conducted in Melbourne in 2000 found that the greatest single cause of vision impairment in Australia in the 40 to 80 age range was uncorrected refractive error (ie not having glasses or not having adequate glasses). However, the most prevalent causes of permanent visual loss were Glaucoma and Diabetic Retinopathy in the under 70s and Macular Degeneration in those over 70 years of age (though most of the common causes of visual loss become more common with advancing age).
Most people with permanent visual loss (Vision Impaired Persons – VIPs) have some useful vision. Their vision can be optimised with updated spectacles or with the use of appropriate ‘Low Vision Aids’ (LVAs).
LVAs include additional lighting, particularly ‘task’ lighting; hand-held magnifiers; stand magnifiers; head mounted loupes; near vision telescopes; distance telescopes; binoculars; spectacle mounted telescopes, etc. Many devices can be supplied with built-in illumination which can be battery or mains powered.
Electronic devices such as closed circuit television (CCTV), computer scanners & displays, voice synthesisers, talking clocks, talking microwaves etc can also be used.
Sadly, it is unusual for optometrists to provide low vision services in their practices; however, at North Lakes Optometry I provide low vision assessments supplementary to routine eye examinations and these would usually be bulk-billed to Medicare or Veteran’s Affairs. I can provide LVAs and Daylight Lamps. I have a kit of commonly used LVAs for people to try and can order other items as required. Simon has an interest in this area of practice as he worked in hospital low vision clinics in the UK as well as running the University of Bradford Low Vision Teaching Clinic from 2002 to 2005. He has also supervised teaching clinics at the QUT School of Optometry Vision Rehabilitation Centre.
For more involved or specific Low Vision Rehabilitation, I can refer patients to one of the ‘local’ services:
- QUT Vision Rehabilitation Centre at Kelvin Grove offers comprehensive multi-disciplinary vision rehabilitation services including Optometry/Low Vision Assessment, Occupational Therapy, Orientation and Mobility Instruction, consultations with a Social Worker of Welfare Officer as appropriate. The clinic can provide LVAs and CCTV (including arranging home demonstrations), and can provide reports for the patient’s GP, optometrist or ophthalmologist, Guide Dogs Queensland and the Commonwealth Rehabilitation Service.
- Low Vision Care Centre, Greenslopes Hospital
- Paediatric Low Vision Clinic, Low Incidence Unit – Visual Impairment Services, Buranda (for children in the education system).
- Guide Dogs for the Blind Association of Queensland, Bald Hills