Ординатура / Офтальмология / Английские материалы / Eye Essentials Binocular Vision_Evans_2005

Accommodative anomalies

108 What are accommodative anomalies?

Accommodative anomalies are problems characterized by an inadequate amplitude or control of accommodation.The various types of accommodative anomaly are listed along the top row of Table 8.1 and they are fairly well defined by their clinical characteristics, also listed in Table 8.1.

How do I investigate?

The first suggestion of an accommodative problem usually comes from the patient’s symptoms (Table 8.1). Careful refraction is essential, and it is usually necessary to rule out latent hypermetropia by cycloplegic refraction. Accommodative amplitude is easily measured with the push up test, typically using the RAF rule (see Table 8.2). Amplitude can also be assessed with negative lenses, although this method gives different results to the push up test.

Accommodative facility (the rate at which the accommodation can be changed) is usually measured with flippers (Figure 8.1). The procedure for this test is described in Table 8.3.The range of responses at this test in a typical population is very wide (Table 8.3) and this makes results difficult to interpret. Undoubtedly, one reason for this is that the test is very subjective. In view of the variability of the test, it is unwise to base a treatment on this test result alone, unless the symptoms are strongly suggestive of accommodative infacility.

It is usual for accommodation to lag a little behind the target, but only by 0.50–0.75D so that the target does not appear significantly blurred. Accommodative lag can be assessed by dynamic retinoscopy and this is the only routine clinical test that can be used to assess accommodative function objectively. It is an extremely useful test, especially with children where a visual conversion (hysterical) reaction is suspected.There are two main approaches to measuring the accommodative lag by retinoscopy. One of these, MEM retinoscopy, is described in Table 8.4.The idea

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Accommodative anomalies

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Figure 8.1 A child being tested with accommodative flippers

behind the test is that it simulates the normal situation when reading and, because the lens is only present briefly and in front of one eye, the accommodation does not relax by the power of the lens. So, the lens power that is required to neutralize the reflex is a true reflection of the accommodative lag.

Accommodative anomalies quite commonly occur in conjunction with other binocular vision anomalies, so a full eye examination is essential to fully understand the problem. In particular, combined convergence and accommodative insufficiency is quite a common condition and can be treated with eye exercises or, in intractable cases, with spectacles.

Another condition which sometimes occurs is spasm of the near reflex.This is characterized by an intermittent spasm of

When do I need to do something?

convergence, accommodation and pupillary miosis. Parents might report an intermittent esotropia in conjunction with a small pupil and the child may report blurred vision together with diplopia.

This can be linked to a variety of neurogenic and psychogenic conditions, so referral to exclude these conditions is advisable. If these are excluded, then treatment with exercises or glasses can be helpful.

When do I need to do something?

Patients who have the symptoms and signs of an accommodative anomaly (Table 8.1) require treatment, once other causes have been excluded. Other causes of their symptoms and signs will generally be excluded by a routine eye examination. Particular care should be taken to look for signs of nervous system pathology (for example, see Table 3.3).

Accommodative anomalies

Table 8.3 Procedure for testing accommodative facility with

112flippers

1.Usually, ±2.00D lenses are used, although ±1.50 or ±1.00 can be used if the ±2.00 cannot be cleared

2.Start with the plus lenses, explaining to the patient that they have to report when the target becomes clear and single

3.The best target is one that can be used to control for suppression, such as the OXO target that is designed to test for vertical fixation disparity

●In facility testing, this target is used simply for the child to report if they experience suppression, when one of the green strips will disappear

●The child will need to wear polarized filters

●The use of this target means that the patient has to report not just when the OXO becomes clear and single, but also when both green strips are present

●For some children, this makes the test too complicated, in which case the test might have to be carried out without checking for suppression

4.As soon as the target is described as clear and single with no suppression, flip the lenses to the pair of minus lenses. Ask the child to again report when the target is clear, single and both strips are present

5.Repeat 4, flipping to the plus lenses

6.Continue, measuring how many cycles can be completed in

1 minute (cycles per minute; cpm). Note that one cycle is two flips

7.The binocular list norms are that about 90% of the population perform better than 2 cpm and about 50% of the population perform better than 7 cpm. If there is an abnormal test result binocularly, the test can be repeated monocularly

If the visual acuity is normal at distance but abnormal at near then this supports the diagnosis of an accommodative anomaly. As mentioned above, latent hypermetropia needs to be excluded and the usual way of doing this is to carry out a cycloplegic refraction.

What do I do?

1.The retinoscopy is carried out at the patient’s usual reading distance

2.The patient wears any refractive correction that they usually use for reading

3.The patient fixates a target on the retinoscope. Because the target is in the plane of the retinoscope, no correction needs to be made for working distance

4.The target is viewed binocularly, although the retinoscopy is of course only carried out on one eye at a time

5.Retinoscopy is usually only carried out in the horizontal meridian

6.Typically a “with” movement is seen indicating that the accommodation is lagging behind the target (plus lenses need to be added). An “against” movement suggests accommodative spasm (see Table 8.1)

7.Spherical lenses are introduced of a power that it is thought will neutralize the reflex. For a typical “with” movement, the first lens might be +0.50

8.The lens is introduced monocularly and is rapidly interposed: it

should be present for no more than 1/2 second.This should be just long enough for a “sweep” of the retinoscope to see if the reflex is now neutralized

9.If the reflex is not neutralized, then steps 7–8 are repeated until the reflex is neutralized

10.Steps 4–9 are then repeated for the other eye

11.The normal range of response (mean ± 1SD) is plano to +0.75D

What do I do?

A sudden-onset marked decrease in the amplitude of accommodation can be a sign of accommodative paralysis, which can result from neurological pathology. Such cases should be

What do I do?

exclude the signs in Table 3.3), the patient can be treated but should be carefully monitored to make sure that the condition does not deteriorate.Treatments are outlined in Table 8.5. A letter of information to the general practitioner is advisable in case the patient presents to them with any other symptoms which, together with the accommodative anomaly, might raise the index of suspicion of pathology.

Index

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Index