Ординатура / Офтальмология / Английские материалы / Pickwell's Binocular Vision Anomalies 5th edition_Evans_2007

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Table 18.1 Clinical observations of nystagmus (modified after Grisham 1990)

Evaluation

Children with new nystagmus, or nystagmus that has not been previously investigated, should be referred. It is disturbing that half of children diagnosed as having CN receive neither visual evoked potential or electroretinogram testing (Budge & Derbyshire 2005). These tests are required for the full evaluation of CN, and optometrists’ referrals should therefore recommend that the patient should be seen in a tertiary centre with the appropriate facilities (e.g. Great Ormond Street Hospital or an eye hospital with paediatric facilities). An important clinical judgement for the optometrist is whether the nystagmus is congenital, latent or acquired. The characteristic features of these conditions are summarized in Table 18.2 to help with differential diagnosis.

Management

NYSTAGMUS 18

Table 18.2 Characteristic features of congenital, latent and acquired nystagmus to aid differential diagnosis

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Table 18.2 (continued )

patients are likely to become more relaxed with each subsequent measurement of their visual acuities, causing an improvement simply because they are less stressed. It is therefore important that any treatment for nystagmus should be evaluated with double-masked randomized placebo-controlled trials (RCTs). A recent review (Evans 2006b) revealed only one RCT of a nystagmus treatment, intermittent photic stimulation (Evans et al 1998). One other intervention, the use of contact lenses, has been shown, by an elegant experimental design, to be very likely to be more than just a placebo (Dell’Osso et al 1988). Other research and theories described in this section await validation with RCTs and should therefore be considered as unproven.

Even when an improvement is shown during or immediately after treatment, the patient has only really been helped if this improvement transfers into everyday life.

Goals of the treatment of nystagmus and aetiology of poor vision

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Eye exercises/vision therapy

Latent nystagmus is often an insuperable barrier to conventional occlusion therapy for strabismic amblyopia. Stegall (1973) reported that the latent nystagmus can be overcome by using a narrow band transmission red filter over the unoccluded eye. He also described two studies that found a reduction in latent nystagmus in the unoccluded eye when a cycloplegic was instilled. In addition to penalization methods, Scheiman & Wick (1994) recommended using anaglyph techniques to treat amblyopia in latent nystagmus and suggested that vision therapy can be effective at reducing latent nystagmus, supporting Healy (1962). Leung et al (1996) reported improvements in a few case studies of CN following vision therapy but there have been no RCTs (Evans 2006b).

Auditory biofeedback

Apparatus has been developed that measures eye movements and translates these into auditory signals (Abadi et al 1980, 1981). Eye movements to the right or left can be converted to sounds in the appropriate earphone and the pitch of the sound made proportional to the magnitude of the eye movement (Abplanalp & Bedell 1983). Case studies and open trials have suggested that treatment using this approach may be effective in albinotic nystagmus (Abplanalp & Bedell 1987), congenital idiopathic nystagmus (Kirschen 1983), sensory defect nystagmus, latent nystagmus and acquired nystagmus (Ciuffreda et al 1982). Clearly, neither the foveal hypoplasia in albinism nor the optic disc hypoplasia in Ciuffreda et al’s (1982) sensory defect nystagmus case can be treated, suggesting that some of the visual loss may have been secondary to the nystagmus, not from the original pathology. There have been no RCTs of auditory feedback (Evans 2006b).

Visual (after-image) biofeedback

A simple form of visual biofeedback can be achieved using an after-image (Stegall 1973, Stohler 1973), and this may be more effective at translating into everyday life than treatment solely based on auditory biofeedback (Abplanalp & Bedell 1983). People with nystagmus usually spontaneously comment that they perceive an after-image to be ‘wobbling’. This movement is related (but not equal in magnitude; Kommerell et al 1986) to their eye movements and it has been suggested that patients can improve their nystagmus by trying to reduce the movement of the after-image (Mallett, personal communication).

An alternative after-image technique (Stegall 1973) is to allow the patient to adopt a head position to reduce the ‘wobble’ as they slowly straighten their head. Goldrich (1981) described a perceptual effect, emergent textual contours, which he claimed allowed nystagmus patients to monitor their nystagmus as an alternative to an after-image method.

Active amblyopia therapy: intermittent photic stimulation

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to future generations. This should be provided by appropriate experts, genetic counsellors, who are usually found in major hospitals and who will accumulate the necessary facts before giving their advice.

The third type of counselling is to give patients or their parents advice that will help them deal with the nystagmus on a day to day basis. For example, if there is a null zone in a certain direction of gaze then a child should be allowed to sit at a position in class that takes advantage of this. People with nystagmus or their families can often receive considerable support from talking to other people with the condition. The Nystagmus Network provides this type of support, and has excellent literature for those affected and their family (www.nystagmusnet.org).

Clinical Key Points

■The main types are congenital nystagmus (CN; onset in first 6 months), latent nystagmus (usually associated with early onset strabismus) and (more rarely) acquired (neurological) nystagmus

■CN can occur secondary to a sensory defect, including albinism, or idiopathic where there is assumed to be a motor defect

■The apparent pattern of nystagmoid eye movements cannot be used with certainty to predict the aetiology of the nystagmus or the level of vision

■All new cases in adults need referral to a neuro-ophthalmologist; new cases in children need referral ideally to a specialist paediatric hospital eye clinic

■Nystagmus often varies over time and at different gaze positions and fixation distances

■There may be an anomalous head position so that the gaze is in a ‘null position’

■High refractive errors are common and contact lenses often improve vision more than spectacles

■Orthoptic problems should be treated if causing symptoms, but patients with albinism are probably unable to exhibit true binocular vision

■There is no cure for nystagmus and claims about treatment should be viewed sceptically: the only randomized controlled trial of a treatment for CN showed the therapy to be no better than a placebo

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APPENDICES

Appendix 1 Confusing aspects of binocular vision tests

There are several potentially confusing aspects of binocular vision tests. This appendix aims to remove some of this confusion and to provide useful mnemonics to help students remember essential ‘rules’.

Binocular vision tests: practitioner’s perspective

General rule: (1) Prism base to correct a deviation is in opposite direction to the deviation or (2) ‘the base of the prism must be on the side of the inefficient muscle’ (Percival 1928).

Binocular vision tests: patient’s perspective

Maddox rod: if RE rod goes up, R hypo, need base-up RE

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