At the completion of this article, the reader should be able to improve their management of accommodation disorders, including:
- Review the three main techniques to determine Amplitude of Accommodation (AA)
- Review the use of the Monocular Estimated Method (MEM) to determine accommodative posture
- Understand accommodative facility, and the test needed to measure it
- Review the five categories of accommodation disorders.
Laura DeAngelis
BOptom, MPhil
Australian College of Optometry, Carlton, Victoria, Australia
Tim Fricke
BOptom, MSc, GCertOcThera, FAAO
Australian College of Optometry, Carlton, Victoria, Australia
School of Optometry and Vision Science, UNSW Sydney, NSW, Australia
Department of Optometry and Vision Sciences, University of Melbourne, Victoria, Australia
When it comes to accommodative dysfunctions, LAURA DeANGELIS and TIM FRICKE say understanding and managing these conditions can help improve patient outcomes, alleviate symptoms and enhance visual comfort and efficiency. Ultimately, early detection and intervention will prevent potential long-term visual issues.
Today’s way of life places a high value on activities requiring close-up vision, such as reading, working at a desk and using computers. However, some people find these tasks challenging due to the requirement for accurate eye alignment and sustained, precise focus. Trying to perform these tasks without these abilities can result in eye strain and tiredness, and affect visual performance.
As society increasingly depends on tasks that demand close-up vision, it becomes more crucial for optometrists to recognise and manage these difficulties.
The near triad
When a person changes fixation from one target at a given distance to another target at an alternate distance, several ocular systems need to be altered to maintain clear, single binocular vision.
The near triad links increased ocular accommodation, convergence and pupillary constriction when a person’s attention shifts to a near object. Accommodation provides near focus using parasympathetic control of the ciliary body to adjust crystalline lens shape via the zonules.1 Age is obviously a common disruptor of accommodation via lens hardening manifesting as presbyopia.2
However, while neurologic or pathologic disruption of accommodation is rare, functional disorders manifesting with symptoms of blurred vision, asthenopia and diplopia are a relatively common finding in children and young people.3
These functional accommodative disorders can affect quality-of-life and might even make school performance worse. That’s why it’s important for optometrists to do the right tests, diagnose the problem and manage it properly to help patients get back to normal vision.4
Diagnostic testing of accommodative function
A diagnostic assessment of accommodative function generally consists of tests probing some combination of four parameters: amplitude, posture, facility and range. Accommodation and vergence systems interact under binocular viewing conditions, so dysfunctions of one system may contribute to problems in the other. The interaction also means that monocular and binocular test results may differ – practitioners should be mindful of the potential accommodation cues present in a test situation (proximity, blur, vergence), controlling each as appropriate to generate repeatable results.5
Ideally, testing should be performed in free space with distance correction in place. It is also worthwhile considering that as the system fatigues, for example towards the end of the day, more abnormal findings may reveal themselves.
Amplitude of Accommodation
Amplitude of Accommodation (AA) is a measure of the maximum dioptric focus attained by the accommodative system. It can be measured using three main techniques, which vary in test time, skills needed, repeatability and results.6 Practitioners should use the one they are most comfortable with and compare to normative results using the same method.
1. Push-up method
Patient views a target monocularly, starting at a distance appropriate for age (40 cm from the eye for a young person), then the target is slowly moved (at a rate of 0.50D/sec) towards the eye until the first reported sustained blur. It is important to use an accommodative target (letters or words in the smallest resolvable print) under good illumination to enhance the patient’s ability to detect blur, and periodically monitor patient response by asking them to read the letters to ensure the target is not blurred. The reciprocal of the ‘near point of accommodation’ (in meters) represents the AA in diopters. Repeated measures can be helpful to observe sustaining ability.7 The ‘pull-away’ method is similar, but starts close enough to be blurred and moves away until reported clear.
2. Minus lens technique
Negative lenses are introduced in front of a monocularly viewed accommodative target in -0.25DS steps with the patient instructed to keep the target clear. The amplitude is measured as the strongest minus lens with which the subject can keep the target clear.6,7
3. Dynamic retinoscopy
With one eye occluded, a near accommodative target should be placed close to the eye and the patient asked to push the target away until it is clear.6 With the target held at this distance, the patient should be instructed to maintain a clear focus of the target while the examiner moves towards them.
Initially an ‘against’ movement is expected; the amplitude can be measured as the inverse of the distance (in meters) at which a neutral reflex is first observed.6 If a ‘with’ movement is observed move the retinoscope away until neutrality is achieved.7
Accommodative posture
Accommodative posture is the difference between the accommodation generated (response) and accommodation stimulus (demand). Patients can have a ‘lag’ or ‘lead’ of accommodation representing either a smaller or greater accommodative response relative to demand, respectively.7,8 Due to depth of focus, the accommodative response can be up to 0.75 D different than stimulus without any appreciation of blur.8
Posture can be measured objectively using the Monocular Estimated Method (MEM). Attach an age-appropriate accommodative target to your retinoscope and instruct your patient to focus on the target. Neutralise the retinoscopy reflex in each eye sequentially by interposing spherical lenses.8
Plus lenses indicate a lag (‘with’ motion) and negative lenses a lead (‘against’ motion). Remember that to minimise the effect of the neutralising lenses on accommodation, the lenses should remain in front of the eye only briefly.3,7 An alternative to MEM is Nott’s method whereby the fixation target is held at a fixed near point while the retinoscope is moved further or nearer until a neutral reflex is observed.8
Accommodative facility
Accommodative facility measures the ability to increase and relax accommodation in response to blur induced by alternating plus and minus lenses. The dynamics of the accommodative response can be assessed by measuring the number of cycles (one cycle represents the ability to clear one set of plus and minus flipper lenses, either with ±1D or ±2D) that can be cleared within a one-minute period while viewing an accommodative target held at 40 cm.
The test should initially be completed binocularly to give measurement of combined accommodative/vergence response, followed by monocular testing for subjects experiencing difficulties with binocular testing.3 It can also be helpful to note the patient’s preference for plus or minus lenses, and, when testing binocularly to check for suppression.
Accommodation ranges
Positive Relative Accommodation (PRA) and Negative Relative Accommodation (NRA) measure the extent that accommodation can change while holding proximity and vergence stable. The patient views an accommodative target at 40 cm through their distance correction. Positive lenses are added binocularly in 0.25 D steps until first sustained blur, giving NRA. Then negative lenses are added to first sustained blur to measure PRA.3
Accommodation disorders & diagnoses
Accommodative dysfunctions can be grouped using the Duke-Elder classification into five categories: insufficiency; ill-sustained; infacility; spasm and accommodation paresis.13 Accommodative insufficiency (AI) is the most frequently diagnosed (80% of accommodative dysfunctions), followed by infacility at 12%.14,15 Accommodation paresis is a rare sudden onset disorder of marked accommodation insufficiency accounting for less than 1% of accommodative dysfunctions and will therefore not be discussed further.
It is important to appreciate that clinical findings may not exactly match those described above. In reality, binocular vision problems may have more than one area affected. In addition, as accommodation and vergence systems are intrinsically linked you should always ensure that your testing and management encompasses both systems.
Accommodation disorders & management
Accommodative dysfunction is common, accounting for around 50% of patients diagnosed with binocular vision problems in optometric practice.16 Commonly reported symptoms such as blurred vision, asthenopia, and diplopia can have a marked impact on quality-of-life, and may contribute to diminished school performance and thus appropriate diagnosis and management of these disorders is critical.4
Uncorrected refractive error can cause accommodative problems.3 The first step in evidence-based management of accommodative dysfunction is therefore to consider how a distance refractive correction would impact the problem. If the accommodative dysfunction persists after correcting any significant ametropia, consider a near addition and/or vision therapy to alleviate symptoms and help patients to regain normal visual function.
A near addition should be considered for patients experiencing difficulty generating accommodation – classically, AI. In patients with AI, one study showed significant improvement in symptoms with both +1.00 D and +2.00 D reading glasses for eight weeks, however AA only showed significant improvements in the +1.00 D group.17 While the study lacked some nuance, it does suggest that keeping near additions lower may achieve better long-term outcomes. The MEM result minus 0.25 D may be a useful guide.
Vision therapy is the other option, and can be used sequentially to refractive correction and near addition, or in place of other options. A literature review up to 1987 concluded that vision therapy was an effective treatment for accommodative deficiencies, but most studies lacked randomisation or control.18 More recently, a large (221 children), well designed (randomised, controlled, and double-masked) study showed that vision therapy can improve both AA and facility significantly more than placebo over a three-month period.19
Vision therapy often works best in older children who can understand and follow directions. It can be performed at home (after in-office instruction), or purely in-office. Either way, compliance is critical to the desired outcome.
When managing any paediatric patient it is vital to clearly communicate your diagnosis, proposed management, including goals for treatment, anticipated timeframe, frequency of reviews, and associated costs to both the patient and their parents/carer. It is also important to discuss with patients the link between accommodative problems and other factors such as fatigue, stress and overwork.
Optometrists should always complete a thorough exam of ocular health especially when faced with potentially neurological symptoms (headache or diplopia) and consider referral if any doubts regarding their final diagnosis. Good communication with caregivers is an essential step for successful treatment.
Conclusion
Accommodative dysfunctions are common in children manifesting as clinically significant symptoms such as blurred vision, asthenopia, and diplopia. Their negative effects on quality-of-life and school performance necessitate appropriate clinical investigation, diagnosis and management to help these patients recover normal visual function.
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References
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- Wahlberg M, Abdi S, Brautaset R. Treatment of accommodative insufficiency with plus lens reading addition: is +1.00 D better than +2.00 D? Strabismus 2010;18(2):67-71.
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