This month sees the start of our new Low Vision (LV) Corner series, authored by Abi Crutcher. Abi begins her series by asking: what is low vision?
Low vision is defined by the Royal National Institute of Blind People (RNIB) as: “An impairment of visual function for which remediation is not possible by conventional spectacles, contact lenses or medical intervention and which causes restriction in a person’s everyday life’1.
According to a report by the RNIB2, there are more than two million people in the UK living with sight loss, with a visual acuity (VA) of less than 6/12. This includes people whose vision could be improved by wearing correctly prescribed spectacles, but who may not be able to for a variety of reasons, such as having additional needs, dementia or simply not being able to afford the correct spectacles. Surprisingly, this latter group represents 39 per cent of the UK’s two million sight impaired people.
Some 340,000 people are registered as sight impaired (SI) or severely sight impaired (SSI), and 24,000 people per year are given a Certificate of Visual Impairment2.
In order to be certified as SI, a person has to have a VA of:
• less than 6/60; or
• 6/24 if they have a reduced visual field.
In order to be certified as SSI, a person must fall into one of the following three categories:
1. People with a VA below 3/60 on the Snellen scale.
2. People with a VA of 3/60 on the Snellen scale or better, but worse than 6/60 on the Snellen scale, who also have contraction of their visual field.
3. People with a VA of 6/60 or better on the Snellen scale and who have a clinically significant contracted field of vision, which is impairing visual function, such as a significant reduction of inferior field or bi-temporal hemianopia.
You may think that you don’t see any low vision patients in your practice. However, the chances are that you do, but you perhaps do not recognise them as such. Anyone with a corrected VA lower than 6/12, or a near VA of less than N6, is classed as visually impaired and could benefit from your advice3.
All dispensing opticians can help patients with low vision as it is a core competency. Further training is available, but it is not essential; having a keen interest is a good place to start.
Causes of low vision
According to the RNIB2, the leading causes of low vision in the UK are:
• Age-related macular degeneration: 48 per cent
• Glaucoma: 16 per cent
• Cataract: 12 per cent
• Retinitis pigmentosa: 10 per cent
• Diabetic eye disease: eight per cent
• Other: six per cent
Each of these conditions will affect the visual system differently, creating varied challenges for the patient4.
Next month, we will look at the impact that visual impairment has on a patient.
References
1. Low Vision Services Consensus Group. Low Vision Services: Recommendations for future service delivery in the UK. London: The Royal National Institute of Blind People 1999.
2. Royal National Institute of Blind People September 2021. Key information and statistics about sight loss.
3. Royal College of Ophthalmologists. Ophthalmic Services Guide. Low vision: the essential guide for ophthalmologists. July 2021.
4. Mangione CM et al. Identifying the content area for the 51-item National Eye Institute Visual Function Questionnaire: results from focus groups with visually impaired persons. Arch. Ophthalmol. 1998 Feb;116(2):227-33.
Abi Crutcher is an extended services contact lens optician with a professional certificate in low vision. In addition to working in practice, Abi represents dispensing opticians on her regional optical committee and, through that, on the Welsh Optometric Committee. She represents optometry on her local primary care cluster committee – and is ABDO’s regional lead in Wales.