Low vision practice VRICS

Closing Date: 18/02/2022

Clinical Practice Clinical Practice

Rather than maximising high contrast acuity, something that is still a major focus of the routine eye examination, a low vision assessment is much more about assessing the residual functional vision of each patient and then attempting to find ways to help the patient maximise use of this vision in their everyday life. As such, it is important to be flexible with your approach to assessment and to use a range of options for testing as appropriate, and also to be aware of a range of management strategies that might be useful. In my view, one of the most interesting things about low vision work is that different management options are nearly always worth trying, new ones are always appearing, and no two patients usually need the same plan, even when on paper they have the same level of vision.

In this VRICS exercise, I have tried to reflect this with regards to the initial assessment and with an example where a number of management options exist.

Testing functional vision 

We all know that there are many, often better, alternatives to Snellen high contrast acuity charts for assessing vision. That said, many of us are still wedded to the 6/6 end goal. For many reasons, using standard Snellen charts and notation has its limits when dealing with reduced vision, not least because we are hoping to represent differently contrasting, differently sized and differently distanced real-world targets, which might be important to someone’s everyday activities.

Visual Fields

The importance of visual fields testing is often under-estimated in many low vision assessments. The key point to remember is that the test is no longer one of disease detection but of assessing disease impact. For this reason, most tests tend to be performed binocularly and the results need to be considered in terms of how they may impact on a patient’s life; in particular, their ability to move about. This last point is important when considering sight impairment certification. When memorising the criteria for sight impairment registration, many a trainee is frustrated by the fact that specific visual acuity values are cited but, when it comes to visual fields, the criteria are more vague and based upon qualitative values such as ‘severe’ or ‘moderate’. This is because, to a large extent, the impact assessment is discretionary. For example, a large superior homonymous quadrant loss may have major implications in identifying vascular disease in the temporal lobe, but would be unlikely to have much impact upon mobility. On the other hand, even a minor inferior encroachment might make walking very difficult indeed and be enough to move someone into a registrable category.

Distance Magnification and Television

Asking for help to view a television is one of the most common requests from the visually impaired. A useful thing to remember, if trying to help someone to see the TV better, is that the height of a 6/6 letter is 8.73mm. 

  • Bill Harvey is a specialist optometrist at the RNIB Low Vision Clinic, London.