Focus on….visual discomfort

Visual discomfort is a broad term describing symptoms such as eyestrain, headache, blur, glare, difficulty sustaining near work and visual disturbance. These symptoms have many possible causes and should not automatically be attributed to visual stress.

Visual stress is a term used to describe a particular pattern of visual discomfort and perceptual disturbance that may be provoked by repetitive or high-contrast patterns, including lines of text. Patients may report symptoms such as:

– movement, distortion or blurring of print

– patterns, shadows or “rivers” within text

– glare or discomfort when looking at text

– eyestrain or headache associated with sustained reading or near work

– difficulty sustaining visually demanding tasks

– sensitivity to particular visual environments or patterns

Visual stress should not be used as a catch-all explanation for reading difficulty or visual discomfort. Historic terms including Meares-Irlen syndrome, Irlen syndrome and scotopic sensitivity syndrome are no longer recommended terminology.

Symptoms attributed to visual stress are non-specific and may also arise from uncorrected refractive error, an inappropriate or poorly fitting optical correction, accommodative or binocular vision anomalies, ocular disease, migraine, dry eye or other causes. These possibilities should be considered before coloured filters are recommended.

Visual stress and dyslexia are distinct.

Dyslexia is a specific learning difficulty and cannot be diagnosed through an eye examination, visual stress assessment, coloured overlay assessment or colourimetry.

The presence or absence of visual stress does not determine whether a person has dyslexia or another specific learning difficulty (SpLD). Similarly, a diagnosis of dyslexia should not lead to an assumption that visual stress or coloured filters will be relevant.

Where dyslexia or another SpLD is suspected, the patient or parent/carer should be advised to seek assessment through an appropriately qualified SpLD professional. For children and young people, the school or college SENCO or equivalent educational support service may be able to advise on appropriate assessment and support pathways.

Current SASC guidance recommends that SpLD practitioners screen for the possibility of visual difficulties but do not incorporate diagnosis or assessment of visual stress into the diagnostic SpLD assessment. Where visual symptoms are identified, referral to an optometrist is normally appropriate so that potential ocular, refractive and binocular causes can be investigated.

A dispensing optician may provide coloured overlay assessment and colour-based interventions where they have undertaken appropriate training, remain competent to do so and work within appropriate clinical governance arrangements.

The GOC requires registrants to recognise and work within the limits of their competence.

A visual stress assessment undertaken by a dispensing optician does not replace a sight test or eye examination.

Before undertaking an assessment, the DO should therefore be satisfied that:

– an appropriate sight test and assessment of ocular health has been undertaken by an optometrist or ophthalmic medical practitioner

– relevant refractive findings have been considered, and an appropriate optical correction has been supplied or trialled where indicated

– any need for further investigation of accommodation, binocular vision or ocular motor function has been addressed by an appropriately qualified practitioner

– there are no symptoms or findings requiring further clinical investigation or referral

Where symptoms are new, unexplained, worsening or inconsistent with the patient’s previous history, the patient should be referred appropriately rather than the symptoms being attributed to visual stress.

Before considering colour, review the patient’s clinical and dispensing records.

Check whether any previously identified optical requirements have not been provided, have not been worn as advised or are no longer appropriate.

Where relevant, consider:

– whether the current prescription is up to date

– whether the spectacles are being worn as intended

– lens design and suitability for the patient’s visual tasks

– centration and positioning of the lenses

– spectacle fit and stability

– working distance and posture

– occupational or educational visual demands

– any recommendations made by the examining optometrist that have not yet been implemented

Where an existing optical or clinical intervention may reasonably explain or improve the symptoms, this should normally be addressed and given an appropriate trial before progressing to coloured filters.

Simple environmental changes may improve visual comfort and should be considered before, or alongside, coloured filters.

Advice may include:

– providing comfortable and even illumination

– reducing glare and reflections from windows, luminaires and display screens

– adjusting screen brightness, contrast, text size and viewing distance

– taking regular breaks during sustained near work

– varying viewing distance during prolonged close work

– maintaining an appropriate working distance and posture

– discussing suitable modifications with the school, college or workplace where appropriate

Such adjustments may benefit many people and a preference for them does not, in itself, establish a diagnosis of visual stress.

Where symptoms persist after appropriate ocular, refractive and binocular causes have been considered and managed, a coloured overlay assessment may be considered.

The assessment should be undertaken only by a practitioner who has received appropriate training and is competent in the technique being used.

The practitioner should:

– establish the nature and circumstances of the patient’s symptoms

– use a consistent and appropriately documented assessment procedure

– avoid suggestive questioning or implying that a particular colour is expected to help

– record any reported change in visual comfort or task performance

– explain that an immediate preference for a colour does not necessarily demonstrate a lasting clinical benefit

Where an overlay appears beneficial, the patient should normally be encouraged to use it in their usual reading or working environment for a suitable trial period.

Continued voluntary use and sustained subjective benefit are more meaningful than a preference demonstrated during a single assessment.

If the overlay is not being used voluntarily, or provides no meaningful ongoing benefit, further colour-based intervention would not normally be indicated.

Where a patient reports clear and sustained benefit from an overlay, precision colour assessment may be considered where appropriate.

The patient should be advised that:

– the preferred spectacle-lens tint may differ from the preferred overlay colour

– the evidence supporting precision-coloured filters remains uncertain

– benefit cannot be guaranteed

– tinted lenses may alter colour perception and the appearance of the visual environment

– the suitability of a tint should be considered for the activities for which the spectacles will be used, including any safety-critical tasks

The clinical rationale, assessment findings and advice provided should be recorded.

A follow-up should be considered to establish whether the lenses continue to provide meaningful benefit. Continued use should not be encouraged simply because the lenses have been supplied.

The evidence base for coloured overlays and precision-tinted lenses remains mixed and contested.

Some individuals report improved visual comfort or reduced perceptual symptoms when using coloured filters. However, there is currently insufficient robust evidence to claim that coloured overlays or precision-tinted lenses reliably improve reading ability, literacy or educational attainment.

Patients and parents/carers should therefore receive balanced information which explains:

– the potential for subjective improvement in symptoms

– the limitations and uncertainty of the evidence

– that benefit varies considerably between individuals

– that there is no guarantee of improvement

– that coloured filters are not a treatment for dyslexia or another SpLD

The cost, time commitment and potential for raised expectations should form part of the discussion before proceeding.

Information provided by practices must be accurate, balanced and capable of substantiation.

Advertising and patient communications must not state or imply that coloured overlays, colourimetry or precision-tinted lenses diagnose, treat or cure dyslexia, ADHD, autism or another specific learning or neurodevelopmental condition.

Practices should avoid:

– claiming guaranteed improvements in reading speed, comprehension or educational performance

– presenting testimonials or individual patient experiences as evidence that an intervention will benefit others

– suggesting that visual stress assessment constitutes a dyslexia assessment or

– implying that coloured filters are clinically necessary simply because a patient has dyslexia or another SpLD

Where research or clinical evidence is quoted, it should be current, relevant and accurately represented.

The availability and funding of coloured filters through NHS arrangements varies across the UK and practitioners should follow the relevant national GOS regulations and guidance.

A visual stress assessment does not create entitlement to an NHS-funded tint.

In England, where a GOS tint supplement is claimed, the tint must be considered clinically necessary and prescribed by the optometrist or ophthalmic medical practitioner who carried out the sight test. It cannot simply be added to the voucher by the dispensing optician during dispensing.

Where colourimetry, overlays or precision-tinted lenses are provided privately, patients should be given clear information in advance about:

– assessment fees

– the cost of overlays

– colourimetry fees

– spectacle and lens costs

– any follow-up charges

– what, if anything, is covered through NHS arrangements