Since opening its doors in 2010, the Hoya Faculty based in Budapest (Figure 1) has been the location of numerous education events, including international sessions aimed at sharing the latest knowledge relating to vision and vision correction. The seventh such event took place last month and included in the various lectures and workshops were sessions discussing fixation disparity and novel ways of assessing and interpreting the concept.
Modern cataract practice
A key presentation on the first day came from Viennese ophthalmologist Nino Hirnschall who gave a useful update on cataract management. He emphasised the importance of discussion with the patient when assessing the impact of lens changes before deciding upon treatment. It is important to establish whether there are symptoms such as glare and blurry vision and stated that ‘patient symptoms are more important than visual acuity’. This has been helped by the introduction of specific questionnaires such as the Swedish Catquest. He also showed how instruments such as the C-Quant have been helpful in assessing the impact of light scatter on the patient’s vision.
Looking for compensation
[CaptionComponent="2338"]Two speakers particularly stood out on the second day. UK clinician and researcher Professor Bruce Evans (Figure 2) discussed spectacle non-tolerance in the first of his two lectures. Citing some of his previous published papers, Evans explained how non-tolerance to a particular refractive prescription was most common in the 50- to 59-year-old patient age group, with 88% in one study being presbyopic.
No gender bias had been found and all cases had been managed with adjustments of 1.00DS or less. His work had suggested that intolerance due to the prescription accounted for just over 60% of cases, with dispensing problems causing 22%, disease 8.5%, data entry errors 6.8% and anomalies of binocular vision just 1.7%. In conclusion, Evans suggested we might view the ‘non-tol as an opportunity’. Good management of the problem should ensure patient loyalty and, indeed, encouraging prescribing and supply through the same outlet should reduce errors.
[CaptionComponent="2339"]Professor Evans’ second lecture reviewed the concept of fixation disparity. Most UK practitioners are aware of the measurement through the work of Ron Mallett when at the Institute of Optometry in London some decades ago. A single image is achieved by two eyes that fixate upon the same point in space. In some people, muscle effort is required to achieve this and, when the eyes are relaxed, tend to adopt positions away from the fixation direction – this is a phoria.
When the effort required to achieve a fixation position and overcome any phoria is too great, then the phoria is said to be decompensated. Fixation disparity may represent this by providing a partially dissociated target (usually with red/green or polarised filters) and the slip of one or both eyes indicative of the decompensation is measurable with prisms.
Professor Roger Crelier from Switzerland (Figure 3) has done much work in this area. After reviewing the various techniques for assessing fixation disparity, including different ways of using alignment prisms such as Mallett’s and the Haases procedure, Crelier introduced delegates to the new ‘EyeGenius’ system in which patients self-adjust their view of test figures using a tablet-based control system and so, it is claimed, avoids the possible errors introduced by the more laborious introduction of prismatic trial lenses before the eyes. Optician will be trialling the new system in the coming weeks.
[CaptionComponent="2340"]Other technology of note included a virtual reality headset (Figure 4) that delegates could link with smartphone software to simulate vision through a range of corrections and various lens designs.
Such dispensing tools are likely to become more familiar in the next few years and it is through events such as these that eye care professionals can ensure they keep up to date.