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

EYE EXERCISES FOR HETEROPHORIA

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Table 10.1 Details of goals and design of IFS exercises

Goal

Design feature

Affordable

Printed home exercises

Easy to understand

Comprehensive instructions

Fun to do

Novel 3-D images

Varied tasks

Motivating

Encourage parent/child team

One or two 10 min sessions daily

Check in 3–4 weeks

Checks on progress

10 self-test questions

Variety of stimuli

18 targets with step and ramp

Different size stimuli

Different shape stimuli

Vergence angles: 3–30

Control/treat suppression

Physiological diplopic images

Monocular markers

Stereopsis

Card 1 introduces the patient to the concept of physiological diplopia, start-

ing with a simple target of two dots. The instructions train the patient to fix-

ate a pencil above the page to cause overconvergence. Patients are taught to

appreciate the page as being doubled, so that they see four dots. The distance

of the pencil is then adjusted and they are taught to be aware of the two

pairs of dots moving until the innermost dots become superimposed. Once

they have practised this they progress to a similar exercise, but with rings. At

this stage the patients experience depth perception and this tends to rejuve-

nate interest. They progress to more dramatic stereopsis, although the sep-

aration of the targets on this card is small, so that only a mild degree of

overconvergence is required.

Quite early on in Card 1 the patient experiences the first of 10 self-test

questions. These ask patients about their stereoscopic perception, to

confirm that they are making appropriate vergence movements. If not,

then they are instructed to stop the exercises and to consult their eyecare

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practitioner.

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PICKWELL’S BINOCULAR VISION ANOMALIES

Card 2

Card 2 uses targets with a very marked stereoscopic relief. In addition to

the conventional ‘ring’ targets, there are also several shapes that are seen

to ‘float in three-dimensional space’ (Fig. 10.11). Throughout this card,

the need to keep the targets clear is stressed, which exercises negative rela-

tive accommodation.

A variety of different techniques are used on Card 2 and there are again

regular self-checks to ensure that the patient is overconverging and not

overdiverging. The awareness of physiological diplopia and stereopsis

should help to reduce any suppression but there are also special targets

that are designed to treat foveal suppression. With these small targets,

the patient sees a four-limbed star ( ) but with some of the limbs seen

only by each eye. Thus, any suppression is revealed and the patient is

taught to overcome this. The patients then progressively ‘jump’ down to

the lower set of rings and repeat the exercises with those. Because these

become further apart they require greater degrees of positive relative

convergence.

After spending some time concentrating on the stereoperception of each

target, patients are then instructed to rapidly track down the page, overcon-

verging as appropriate for each successive target. This represents a form of

‘step’ (phasic) exercises, rather like using prism flippers. In the final stage for

Card 2 patients are taught to gradually move the page towards them while

maintaining an overconverged posture. This represents a form of ‘ramp’

(tonic) exercises.

Cards 3 and 4

To maintain patient interest, Card 3 employs a different approach. It uses

an autostereogram that has been specially created for the exercises (Fig.

10.12). Autostereograms are pictures based on random dot stereograms

and the principle and history of the development of these has been sum-

marized by Thimbleby & Neesham (1993).

Autostereograms can be viewed by converging or by diverging, so great

care is taken in the IFS instructions to ensure that only convergence is used

by patients during the exercises. Patients are taught to first exert positive

relative convergence to obtain a stereoperception and then exert negative

relative accommodation to make the elements of the stereogram clear.

When the stereograms are viewed appropriately, patients perceive a series

of steps, leading up towards them. As ‘their eyes walk up each step’ they

converge by increasing degrees. On each step is a letter, and the patient

has to identify this and record the result. There are the usual ‘self-checks’

to ensure that the exercises are being performed correctly, and the result is

recorded for the practitioner to check at follow-up appointments. As with

the rest of the exercises, the instructions clearly guide the patient through

the stages of this phase of the exercises.

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Card 4 is another autostereogram and follows a similar principle to that

used in Card 3.

One of the main objectives of the IFS exercises is to allow home orthoptic

therapy without the need for much input from the eyecare practitioner.

The exercise booklet can usually be dispensed to the patient without lengthy

explanations. Parents need to be told that the exercises require teamwork

and a quiet time and place for the parent to read the instructions and for

the child to view the cards.

Patients are told that there are self-checks and that they can telephone

the practitioner if they are concerned. They are also warned that the exer-

cises will be hard work so that a few minor symptoms of sore, tired or

aching eyes are to be expected for the first few days. The instructions warn

that, if these symptoms persist or if any blurring or diplopia occur, then

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the patient should stop the exercises and consult the practitioner. Typically,

a follow-up appointment is booked in 3 weeks.

EYE EXERCISES FOR HETEROPHORIA

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CASE STUDY 10.1 Ref. E5380

BACKGROUND: Insurance broker aged 61 years, wearing bifocals with minimal

distance correction and 2.00 add. General health good, no medication.

SYMPTOMS: Last few months when reading eyes feel sore and tired and non-

localized headache about twice a week after day in office.

CLINICAL FINDINGS: Normal: visual acuities, refractive error (minimal

hypermetropia for distance, 2.25 add), visual fields, pupil reactions,

ophthalmoscopic findings, ocular tensions, anterior segment, D ocular motor

balance, NPC (4 cm). N cover test 6 XOP with poor recovery. N aligning prism

(with correction) 2.5 in L. N convergent fusional reserve /8/6 .

MANAGEMENT: Discussed decompensated exophoria and possibility of prism

in glasses or eye exercises. Patient preferred to have eye exercises and given IFS

exercises. Re-exam advised in 4 weeks.

FOLLOW-UP: Found exercises easy, done for 20 min a day. Symptoms ‘cleared

up’ and no headaches. N cover test 4 XOP with good recovery. N aligning prism

(with correction) 0.5 in LE. Convergent fusional reserve 26/34/18. Exercises

stopped, to return if more symptoms.

FOLLOW-UP 18 MONTHS LATER: No symptoms (broken glasses), results as

at last appointment except for aligning prism now zero.

Follow-up

Very rarely, patients telephone the practitioner to report a problem with

the exercises. The problems they might report and solutions to these are

given in the practitioner instructions.

At the follow-up appointment, after 3–4 weeks, the practitioner should

enquire about how easy or difficult the exercises have been, how often

they been done and for how long on average each day (Case study 10.1).

The patient should be asked about any change in their initial symptoms

and whether any new symptoms have occurred.

The relevant clinical tests should be repeated and the results compared

with those obtained before giving the exercises. If the symptoms and clin-

ical signs have improved then the exercises can be stopped (Case study

10.1). Occasionally, the exercises need to be continued for a little longer. If

there has been no or very little improvement then alternative approaches

need to be considered, as discussed elsewhere in this chapter and in

Chapter 6. If the exercises have been successful then the patient is asked to

keep the booklet in case further ‘top-up’ exercises are required. Most older

patients recognize the return of their symptoms and initiate a further ses-

sion of exercises themselves. Of course, patients should be warned that if

symptoms persist they should return. Younger patients may need to be

re-examined, perhaps in 3 months, to check the clinical signs. Patients can

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be reassured that top-up exercises are usually much easier and briefer.

impair stereopsis.

(2) Aniseikonia: when the lenses are of different powers, there will be a

larger retinal image in one eye than the other because of the difference

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in spectacle magnification.

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PICKWELL’S BINOCULAR VISION ANOMALIES

These two problems are discussed in more detail below. In both cases, these

difficulties will cause more problems in older patients, with previously

uncorrected patients or where a large change in prescription is given.

Prismatic effects

Diagnosis

The main factor in recognizing a difficulty due to prismatic effects is the

presence of the anisometropia itself. It may also be found that older chil-

dren and teenage patients with anisometropia have spasm of accommoda-

tion, and where this is suspected a cycloplegic refraction should be carried

out. The symptoms of the anisometropia will be those due to the type of

refractive error in the better eye: asthenopia for near vision in hyperme-

tropia and blurred distance vision in myopia. Some patients may be hyper-

metropic in one eye and myopic in the other. In these cases, they may use

one eye for distance vision and the other for close work. If there is no sig-

nificant refractive error in one eye, the patient may have no symptoms.

This may also be true in cases where no glasses have been worn and sup-

pression has developed.

Many patients will experience no problems when spectacles are pre-

scribed; the younger the patient when glasses are first worn the more likely

it is that trouble can be avoided. This is probably because patients with

stable binocular vision or compensated heterophoria can usually adapt to

prismatic effects in a very short time (Carter 1963). The symptoms that

occur when the patient does not adapt to the correction for anisometropia

consist of difficulties in getting used to the new glasses: typically headache

or intermittent diplopia. Troubles seldom occur when the anisometropia is

less than 2 D. If spectacles that fully correct the anisometropia can be tol-

erated in childhood then the prognosis for successful spectacle wear in

adult (pre-presbyopic) life is good, since anisometropia usually gradually

reduces over the years (Ohlsson et al 2002b).

Investigation and evaluation

Often, these difficulties can be avoided by anticipation. A partial correction

is given in the more hypermetropic eye in those cases where there has

been no previous correction or where there is a large difference between

the previous correction and the new one. The extent of this modification

to the prescription can be determined by the Mallett fixation disparity test

or the infinity balance ‘nodding test’ (Ch. 9). The patient looks at the fix-

ation disparity vertical target through the full correction and is asked to

move the head vertically up and down in a nodding movement so that the

eyes look through the lenses above and then below the optical centres. If

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a vertical fixation disparity is induced then the prescription is modified

until this does not occur. An alternative method is to carry out the cover test

ANISOMETROPIA AND ANISEIKONIA

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with the eyes looking through the near visual points and again when looking

through the optical centres. The power of the more positive lens is reduced

until a good recovery movement to the induced hyperphoria occurs.

As a rough guide, the prescription for the more hypermetropic eye is

reduced by one-third of the change in the anisometropia (the difference

between the two eyes) compared with the previous prescription. This will

mean that it is reduced by one-third of the anisometropia in the case of a

patient who has worn no previous glasses. However, it must not be assumed

that all patients with anisometropia will experience difficulties with their

new glasses. Some patients with marked anisometropia will settle very read-

ily to a new prescription, whereas others with low degrees will experience

symptoms.

Patients often learn very quickly to turn the head rather than the eyes, so

that they always look through the optical centres of the lenses. It sometimes

helps to encourage patients to do this. If the patient needs bifocals then

round top segments of different sizes in each lens can be used to control the

vertical prismatic power in the reading portion. A more detailed coverage of

this subject can be found in Rabbetts (2000). Optically, the best approach is

to fit contact lenses, which move with the eyes so that no prismatic effect is

induced and which also reduce aniseikonia (Evans 2006a). Refractive sur-

gery has been advocated for similar reasons (Paysse et al 2006).

Aniseikonia due to spectacle magnification

differences

Most aniseikonia arises from the difference in spectacle magnification that

accompanies anisometropic corrections; this type may be called acquired

optical aniseikonia. Other types will be considered separately later in this chap-

ter. Interestingly, everyone experiences aniseikonia in asymmetrical conver-

gence of the eyes, for example when converging to an object in our peripheral

vision which will be closer to one eye than the other, and this may become of

the order of 5–10% or more. This physiological aniseikonia appears to be auto-

matically compensated and gives rise to no symptoms (Romano 1999).

Investigation

The possibility of an aniseikonic problem occurring can be foreseen largely

from the presence of the anisometropia, particularly when there is a dif-

ference in spectacle magnification of more than 2% (some authors say

5%). This means that anisometropia of as little as 1.25 D may cause clini-

cally significant aniseikonia, although the precise value will depend on

the prescription, the back vertex distance and the relative ocular dimen-

sions (Rabbetts 2000). Typically, 1 D of anisometropia causes between 1%

and 1.5% of aniseikonia (Borish 1975, p 272).

There is a large variation between people in the amount of aniseikonia

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that they can tolerate (Romano 1999). Again, symptoms will consist of the

Management

Anticipation of the difficulties is again very important. The following

should be considered:

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(1) Warn the patient that difficulties in space perception may occur dur-

ing the first few days of wearing the new glasses. It is usually adequate