Ординатура / Офтальмология / Английские материалы / Binocular Vision and Orthoptics Investigation and Management_Doshi, Evans_2001

Summary and management

1I8 Binocular Vision and Orthoptics

Literature on benign superior oblique myokymia

Benign superior oblique myokymia is an episodic small-amplitude nystagmoid intorsion and depression of one eye, accompanied by visual shimmer and oscillopsia. The condition was originally called unilateral rotary nystagmus (Plager, 1999). The onset is in adulthood and the symptoms are acknowledged to be 'most annoying'. whilst the 'diagnosis is often missed' (Von Noorden, 1996. p. 456). Episodes usually last from 20 seconds to several minutes. and can be triggered by physical activity (von Noorden, 1996. p. 456) and by fatigue and stress (Plager, 1999). The author has been unable to find an estimate for the prevalence ofthis condition.

Superior oblique myokymia is usually benign. but there have been at least two cases of association with a posterior fossa tumour (von Noorden, 1996). Plager (I 999) felt that neuro-lmaglng was unnecessary unless there were other neurological complaints.

Although the precise aetiology is unclear (von Noorden, 1996. p. 456). superior oblique myokymia may be the result of prior clinical or subclinical injury to the trochlear nerve (Mehta and Derner. 1994). Medical treatments have been found. as with this patient. to be generally disappointing (von Noorden, 1996. p. 456; Plager, ] 999). Surgical approaches are sometimes successful. although second operations may be required (von Noorden, 1996).

Discussion

This case seems to be a fairly classic presentation of superior oblique myokymia. The history of patching in childhood is vague. but it seems at least possible that the patient had a superior oblique paresis at this time and that the present symptoms from superior oblique myokymia are linked to this early episode. It would have been useful to have obtained more concrete information about the date of onset of his anomalous head position. It would have been a good idea to examine childhood photographs to determine this.

Diagnosing a superior oblique underaction

Diagnosing subtle vertical incomitancies can be very difficult. A Lees screen test gives a similar result to a Hess screen test. and the results of either of these tests help a great deal (Evans. 1997. pp. 200-203; see also Chapter 12). A computerized Hess

screen is now available for use in optometric practice. However. in subtle incomitancies even Hess or Lees plots do not always clearly identify the under-acting muscle(s). Another approach is to use one of the two three-steps tests (Evans. 1997. pp. 205-6). Parks' three-steps test is best known; however. in heterophoric incomitancies, as in this case. Scobee's three-steps test sometimes provides clearer results. These tests involve asking three questions. which can usually be answered by carrying out dissociation tests at distance and near and with different head positions. The three-steps tests can give invalid results (Plager, 1999) when: more than one muscle is involved. there is a restrictive aetiology (e.g. a blow-out fracture; see Chapter 12). or there has been prior strabismus surgery.

In the double Maddox rod test. two Maddox rod lenses are placed. one in front of each eye. to measure any cyclodeviation (Phillips and Hunter. 1999). The rods are placed exactly vertical in a trial frame. If there is no vertical deviation. then a vertical prism is introduced to separate the horizontal lines seen by each eye. The orientation of the Maddox rod in the trial frame can be adjusted until the two lines are parallel. This gives a measure of the cyclodeviatlon, but does not differentiate a cyclophoria from a cyclotropia. A significant cyclodeviation suggests the involvement of an oblique muscle.

Simons et al. (1994) stated that the double Maddox rod test is the standard test for determining the laterality and size of a cyclodeviation resulting from a superior oblique paresis. It is unusual for a single superior oblique muscle palsy to cause an excyclotropia over 8°: a bilateral superior oblique palsy often causes an excyclotropia over 12° (Spector. 1993). Originally. it was recommended that a red Maddox rod should be placed in front of the right eye and a white one in front of the left eye (Von Noorden, 1996. p. 190). Theoretically, the eye with the underaction would be the one whose image was cyclotorted, although von Noorden noted that exceptions to this rule are common. Simons et al. (1994) explained these exceptions with an experiment demonstrating that a white rod was less disruptive to vision than the red rod. They recommended that two red rods be used. in which case the paretic eye is correctly diagnosed in 94 per cent of cases. Unfortunately. the author had not read this

paper when he saw the patient. so he used a white and a red rod.

Discussion of management

The author has been unable to find any previous suggestions in the literature that a refractive correction with a small vertical prism in the primary position might help patients with superior oblique myokymia. However. Plager (1999) noted that cases of superior oblique paresis that are small and relatively comitant may benefit from prisms. In view of the inadequacy of vertical fusional reserves to overcome many small vertical deviations. this approach would seem to be common sense. Since the vertical prism seemed to help the patient. it is surprising that the previous glasses had not helped. Although the prism in these was a little weak. it should have been better than nothing. The impression from talking to the patient was that he had not been clearly instructed in when to wear these. and he assumed that they should be worn for distance as well as near. Of course. they were blurred for distance vision so he did not use them.

The change in symptoms of superior oblique myokymia with a change of office lighting is interesting and is not reported elsewhere in the literature. With hindsight. it would have been interesting to have asked the patient whether he had been under more stress at about the time that the office lighting changed. since stress can precipitate superior oblique myokymia.

Some people are sensitive to fluorescent lighting. and such photosensitivity can cause various ocular and somatic symptoms. including headaches (Wilkins. 1995). In these cases individually prescribed coloured filters (e.g. precision tints) can help ease symptoms, as described in the final case study in this chapter. However. with Mr D it seems that his symptoms were almost completely resolved with the vertical prism. and he no longer felt that it would be worthwhile investigating any further benefit from tinted lenses. This highlights a fact that is discussed in the last case study below - that so many of the symptoms we try to treat are non-specific.

Congenital nystagmus:

Mr James D, F8591

Personal details and background

The patient is a 35-year-old man who works as a laboratory analyst. sometimes

Case studies III 119

appeared normal and he demonstrated stereo-acuity, so it does not seem that the nystagmus in this case results from albinism. Criticisms of the clinical data are that stereo-acuity tests at near should have been carried out whilst the patient wore his glasses, and colour vision and dark adaptation tests would also have been useful additions.

Congenital nystagmus can be secondary to a disease that impairs visual acuity (sensory defect congenital nystagmus), but Mr D achieves good acuity in his null zone (6/9), so this also appears unlikely.

A tentative diagnosis of congenital idiopathic nystagmus (motor defect nystagmus) seems most appropriate, although objective eye movement recording and electrodiagnosis would be required to confirm this diagnosis (see Chapter 13). In children, when nystagmus is first detected or investigated, such testing is indicated. In adult cases where the nystagmus has been present since the first few months of life, has not changed and was investigated by an ophthalmologist in childhood, referral for further tests is not usually indicated.

About 8 per cent of people with congenital nystagmus have a markedly reduced amplitude of nystagmus at near compared with at distance (Abadi and Dickinson, 1985), and this has been called a convergent null position. Nystagmus blockage syndrome is probably a rare form of congenital nystagmus in which a reduction of the nystagmus during convergence appears to have resulted in an esotropia (von Noorden, 1996, p. 481). Put another way, the patient may have developed an esotropia in order to create an over-conver- gent posture that reduces their nystagmus. It is interesting that this particular patient's refractive error means that he can over-ac- commodate to induce a convergent strabismus that 'blocks' the nystagmus and hence improves the acuity. For a patient of Mr D's age, the limited accommodative amplitude means that this strategy, although momentarily effective, is not suitable for sustained alleviation of his symptoms. Similarly, by lowering his chin and looking up he can achieve surprisingly good acuities; but this is not appropriate for sustained viewing as it could result in a strain to the neck.

It seems that the present glasses were prescribed after cycloplegic refraction and the author suspects that these are close to the full refractive correction. However, testing suggested that the distance vision is

a little clearer and more comfortable with a slightly less strong correction and so the maximum plus that the patient could tolerate for clear distance vision was prescribed. This is a little stronger (more similar to the correction prescribed after a cycloplegic) than the subjective findings.

The situation for reading is quite different. Here. even when the patient wears the glasses and is esophoric instead of esotropic. the nystagmus is milder than at distance (owing to convergence to his habitual reading distance at 25 em) so the

visual acuities are proportionately better than at distance. There is, however, a very large and poorly compensated esophoria at near, resulting from a high AC/A ratio. This esophoria 'broke down' to an esotropia during repeated covering during the cover test, and the negative values in the measurement of the divergent fusional reserves demonstrate that the subject needed baseout prisms to regain fusion once he had been 'broken down' with base-in prisms.

These findings suggest that the patient is constantly straining to prevent a conver-

gent strabismus and it seems very likely that this is the cause of the intermittent blurring and diplopia, and may be a factor in the headaches. A stronger pair of reading glasses have been prescribed. which, through the high AC/A ratio. should significantly reduce the esophoria. A prism has also been prescribed in the reading glasses to correct the vertical deviation, which should help fusion too. The foregoing was explained to Mr D, who felt that separate distance and near glasses would be quite manageable for him.

Itmight be thought that reducing the patient's esophoria at near with stronger glasses might reduce the effect of convergence at dampening the nystagmus. However, the literature suggests that the reduction or the intensity of nystagmus that can occur at near is not mediated by

glasses will not significantly change the angle between the visual axes (they should eliminate the fixation disparity, but this is typically only a few minutes of arc). Hence, strengthening the glasses would not be expected to worsen the nystagmus signiticantly, and the patient should still be able to achieve the 6/9 (equivalent) at near that was possible with the old glasses.

The point made above, that changing the angle bet ween the two visual axes to make the patient more convergent will dampen the nystagmus, suggests that one line of treatment, prescribing base-out prisms, might help. This is not a universal treatment: most cases of congenital nystagmus do not show a reduction at near (Abadi and Dickinson, I 9H5), and there may even be an increase in intensity at near (Ukwade and Bedell, 1992). However, in this case such an approach would be expected to help, although this was not tried since the normal convergence during near vision dampens this patient's nystagmus to a satisfactory degree - he can easily read all print sizes that he encounters.

People with congenital nystagmus often lind that their nystagmus is dampened slightly with contact lenses. Ideally, these should be gas-permeable hard lenses. However. Mr ]) has tried these and is unable to tolerate them. [I'he can be fitted with soft toric lenses and prescribed reading glasses to wear over the top 1+2.00J)S with It. down left eye), this might prove the best achievable form of correction. This was discussed with the patient and he was keen to investigate this mode of correction. He was advised to find a cont act lens practitioner nearer home Ihe had travelled .2 50 miles for his appoint- mcnt I.

The patient was advised that, if the headaches persist, then he should return to his (;1' and ask for a neurological investigation oflllese.

Decompensated exophoria and Meares-Irlen syndrome; Steven R

Personal details and background

Steven was referred by his optometrist to the Institute of Optometry Specific Learning Difficulties Clinic, where he was seen by colleagues. His age at the first appointment was 10 years and h months.

History

•Steven has been diagnosed as dyslexic and his reading age is 2 years 3 months behind his chronological age.

•Delivery was by Caesarian, and he was jaundiced at birth.

•There were no abnormalities in Steven's early development.

•There is no history of refractive correction, eye surgery or orthoptic exercises.

•In 1989 Steven was patched for 6 months for the lack of a reference eye.

•There is a family history of specific learning difficulties (father), convergent strabismus (brother) and migraine (father).

Clinical findings

The symptoms and clinical findings with this patient are summarized in Table 1 h.l.

Discussion

Dyslexia

Dyslexia is an unexpected problem in learning to read in children who seem otherwise capable and intelligent (Evans, 1993a). The diagnosis of dyslexia is usually made by an educational or child psychologist. If a child has 'normal intelligence', adequate opportunity to learn, and yet has a reading age more than 18 months behind his or her chronological age, then they are likely to be dyslexic. There is a genetic component to dyslexia and, as in this case, it often runs in families.

The main cause of dyslexia is likely to be a difficulty in converting a visual representation of text into sound units - a difficulty with phonological decoding. Although visual deficits are not thought to be the major cause of dyslexia, there are various visual correlates of dyslexia. These are visual anomalies that are especially likely to be present in dyslexia, and some of these visual factors can be contributory factors. Although optometrists are unlikely to 'cure' dyslexia, they can in some cases aid reading directly through reducing visual

perceptual distortions and indirectly through removing asthenopia.

The two most common ocular motor anomalies in dyslexia are binocular instability (see Chapter 6) and accommodative insufficiency (see Chapter 1 I. Binocular instability is characterized by low fusional reserves and an unstable hcterophoria (e.g. variable slip on a Mallell unit OXO test). Accommodative Insulllciency is characterized by a low amplitude of accommodation, and may be associated with accommodative infacility. A useful objective method of assessing accommodat ivc function is MEMretinoscopy (see box l.

MEM retinoscopy

The accommodative lag can be measured by retinoscopy using the monocular estimate method (MEM; Cooper, 1987), The subject binocularly fixes a detailed target on the retinoscope and is asked to keep this clear. Retinoscopy is carried out along the horizontal meridian, and lenses are very briefly held in front of each eye-to neutralize the retinoscope reflex, Each lens should only be present monocularly and for a split second so as not to disrupt the status of the patient's accommodative and binocular response. The accommodative lag is usually about +0,75 D: values greater than +1.00 D may represent aecommcdative Insufficlency. Ifa negative lens is required to neutralize the reflex, this suggests that accommodatlve spasm Is occurring. This test may gi ve useful additional Information when there is a low amplttude of accommodation, and with unco-operative patients.

For over 50 years there have been various theories relating dyslexia to ocular dominance, and one of the most recent or these relates to the reference eye (Evans, 1993b). The reference eye is determined with the Dunlop Test, which uses a synoptophore to induce a fixation disparity. The eye that maintains precise fixation is said to be the reference eye. This is not necessarily the same as the eye that is dominant for other tasks, such as sighting dominance. The Dunlop Test is repeated I (J times to assess whether the reference eye is always the right or always the left. or

Table 16.1 Symptoms and clinical findings for Steven R

IDee 94-

Uses glasses for most le

No symptoms: no head

no longer rubs eyes, bl

excessively, or skips or

words or lines

R 6/5. plano L 6/5. +0.2

Ortho

6t.XOP

No prism. stable

No prism. stable

~~ eso, i t. R hyper

6t. exo, nil vertica I

3A1D

-/11/10

12/19/20

Z' each eye binocularly

7'RE monocularly,

5' LE monocularly

Break 6 em. recov, 7 em

R. S D: LSD: B.9D

Motility: full Accommodanve Lag:

R +050. L +0.75 Intuitive colorimetry: results as at 31 Mar 94

No change. continue a

whether it varies. According to advocates of this test. an unstable reference eye is a sign of poor visuomotor control or binocular instability. The intervention that has been suggested to resolve this 'anomaly' is to occlude the left eye for all near vision tasks for some months. There was a lot of research on the Dunlop Test and it became quite popular in the 1980s; however, several studies disputed the original findings and it became generally agreed that the Dunlop Test is usually unreliable. If the Dunlop Test really does attempt to detect a form of binocular instability, then it may be appropriate to apply a battery of tests, including the Mallett unit fixation disparity test, to assess

the binocular stability. The author is unaware of any published studies investigating whether binocular instability is best treated by patching or by orthoptic exercises.

Meares-Irlen syndrome is characterized by symptoms of asthenopia and visual perceptual distortions which are alleviated by individually prescribed coloured filters (Evans et al., 1996). The required colour varies from one person to another, and often needs to be prescribed with some degree of precision (Wilkins et al., 1994). Typically, patients are screened with coloured overlays to determine whether they are likely to benefit from coloured lenses. If the results of the screening are

positive, then patients are investigated with a specialist instrument, the intuitive colorimeter, which is used to determine the optimal colour for precision tinted spectacles or contact lenses. For sound optical reasons, the colour that is required for glasses will be different to the colour that is required for overlays (Lightstone et al., 1999).

One of the challenges for eye-care practitioners who choose to specialize in dyslexia is the non-specific nature of the visual symptoms that may be present. For example, visual perceptual distortions (e.g. blurring, words moving) and asthenopia could result from uncorrected refractive errors, orthoptic anomalies, accommodative anomalies, Meares-Irlen syndrome, or even some forms of pathology. So, which conditions should be looked for and/or treated first? Lightstone and Evans (1995) addressed this issue by suggesting a sequential management plan, which is summarized in Figure 16.1. This protocol is conservative in that optometrists treat the conventional factors first (e.g. refractive errors and orthoptic anomalies), and only try coloured filters once any conventional anomalies have been corrected.

First appointment (16 September 1993)

The blurring of text and skipping of words or lines and re-reading are non-specific symptoms that could arise from a number of conditions. The cover test reveals a fairly large exophoria at near. Ideally, the records should contain a comment on the adequacy of the recovery movement. The size of an exophoria is a poor predictor of whether it is compensated, but the presence of an aligning prism of 2~ strongly suggests that it is decompensated (see Chapter 6). In addition to the Mallett unit, another useful indicator of whether a heterophoria is compensated is Sheard's criterion. This says that the opposing fusional reserve to blur point should be at least twice the heterophoria (see Chapter 6). In this case, the convergent fusional reserve to the blur point should be at least 12-16~ whereas it is only 10~. The NPC is also a little remote. Taken together, these findings suggest a decompensated exophoria at near, as described in Chapter 6.

The amplitude of accommodation is also a little low, although 8 D should allow com-

124 Binocular Vision and Orthoptics

fortable reading at 30 ern. A criticism is that the accommodative lag was not tested. Push-up near point of convergence exercises might be expected to improve the NPC and perhaps to improve the amplitude of accommodation and the convergent fusional reserve. The latter effect might help the patient to overcome the exophoria.

Second appointment (8 November 1993)

Compliance with the exercises appears to be good. An improvement in symptoms is obviously good news, but could result from a placebo effect. It is much more encouraging if there is also an improvement in clinical tests, especially those for which the patient could not predict a 'good' response and which are dissimilar to the procedures used in the exercises.

There has been an improvement in the NPC and stereo-acuity, but although the Mallett unit result has improved it is still a little unstable. The fusional reserve and amplitude of accommodation have not improved and, if anything, have worsened. The patient was therefore given the Institute IFS exercises (see Chapter 6 to treat the convergent fusional reserve).

Third appointment (20 December 1993)

The reading age appears to have improved by 9 months in an interval of only 3 months. Such reports are always encouraging, but caution needs to be exercised because of the large margins of error that are associated with measurements of the reading age and because of the possibility of placebo effects and non-visual factors.

The cover result is unchanged, and this is to be expected. There have been improvements in: the stability of result in the Mallett OXO test, convergent fusional reserves, foveal suppression (binocular status) test, stereo-acuity, and amplitude of accommodation. The patient now passes (Chapter 6) Mallett's criterion (no slip on OXO test) and Sheard's criterion (fusional reserve that opposes the heterophoria at least twice the heterophoria). There is no foveal suppression, and Steven achieves the test ceiling of the Randot circles test. The amplitude of accommodation is still below age norms, but likely to be adequate for sustained reading. It is again unfortunate that the clinician did not assess the accommodative lag. It may also have been useful to assess the accommodative

facility, although this test has been criticized (Kedzia et al., 1999).

It was felt at this time that the binocular and accommodative function were within acceptable limits and were unlikely to benefit from any further treatment. At this stage Steven was tested with the Intuitive Overlays (IOO Marketing Ltd, London), which are a screening tool for MearesIrlen syndrome. Steven showed a consistent response to this testing, and was issued with an overlay of his preferred colour. Patients are instructed to use the overlay ifand when it helps. If there is a voluntary sustained use and parents or teachers notice an improvement in reading fluency, then patients are instructed to return for testing with the intuitive colorimeter.

Fourth appointment (31 March 1994)

Steven had found the overlay to be helpful and was still using it after 6 months. Refractive findings were unchanged, and the orthoptic status was within acceptable limits. He was tested with the intuitive colorimeter (Cerium Visual Technologies, Tenterden). This is an instrument, developed by Professor Arnold Wilkins whilst he was at the MRC Applied Psychology Unit, which allows practitioners to determine the optimal colour of lens for a person to use. For reasons relating to colour adaptation this is likely to be different to the optimal colour of overlay, and a recent study showed that it is inappropriate to prescribe coloured glasses to match an overlay colour (Lightstone et al., 1999). Steven showed a consistent response to this testing, and was issued with a prescription for precision tinted spectacles.

Fifth appointment (l December 1994)

Eight months after being prescribed precision tinted glasses, Steven reports using them frequently and describes an improvement in symptoms. A recent clinical audit at the Institute of Optometry investigated whether patients were still using their spectacles 1 year after prescribing (Evans et al., 1999). More than 80 per cent of those who were prescribed precision tints were wearing them daily, which compared favourably with data for non-tinted spectacles.

Steven's refractive and orthoptic status are unchanged and the improvement in his fusional reserves following the exercises

has been maintained. Accommodative amplitude is still a little low, but the accommodative lag is within normal limits, suggesting that the accommodative accuracy is adequate for accurate reading.

The chromaticity of his optimal coloured filter was checked with the intuitive colorimeter, and the result was unchanged. He was advised to continue as now, and to return for annual checks. The precision tint that a person needs can change with time, and this is usually checked on a yearly basis, or sooner if problems occur.

Additional notes

This case has been selected because it illustrates the most common aspects of optometric involvement in managing people with specific learning difficulties. Many people with these difficulties have perfectly normal visual function and require no optometric treatment. Some patients have ocular motor problems (binocular or accommodative) and these people frequently have their symptoms cured by optometric treatment, such as eye exercises. Other cases have Meares-Irlen syndrome and require coloured filters to alleviate their symptoms. The interesting feature of this case is that Steven required orthoptic exercises and coloured filters to alleviate his symptoms fully.

Acknowledgement

Some of the appointments for the final case study were with colleagues at the Institute of Optometry.

References

Abadi, R. V. and Dickinson, C. M. (1985). The influence of pre-existing oscillations on the binocular optokinetic response.

Ann. Neurol., 17, 578-86.

Abadi, R, V, and Dickinson, C. M. (1986). Waveform characteristics in congenital nystagmus. Docum. Ophth., 64, 153-67.

Cooper, J. (1987). Accommodative dys-

Diagnosis and Ma1JiI.qemenf

0. F. Amos, ed.), pp. 431-

59. Butterworths.

Evans, B. J. W. (1993a). An overview of dyslexia: a specific learning disability.

Optom. Today, 33, 28-31.

Evans, B. J. W. (1993b). Dyslexia: the

Dunlop Test and tinted lenses. Optom. Today, 33. 2h-30.

Evans, B. J. W., Wilkins, A. J., Brown, J. et al. (19%). A preliminary investigation into the aetiology of Meares-Irlen Syndrome. Ophthal. Physiol. Opt .. 16, 286-

96.

Evans, B. J. W. (1997). Pickwell's Binocular Vision Anomalies, 3rd edn. ButterworthHeinemann.

Evans, B. J. W.. Patel. R., Wilkins, A. J.et al. (1999). A review of the management of 323 consecutive patients seen in a specific learning difficulties clinic. Ophthal. Physiol. Opt .. 19,454-66.

Evans, B. J. W. (2000). An open trial of the Institute Free-space Stereogram (IFS) exercises. Br.]. Optom. Disp., 8,5-14.

Kedzia, B., Pieczyrak, D., Tondel, G. and Maples. W. C. (1999). Factors affecting the clinical testing of accommodative

facility. Ophthal. Physiol. Opt., 19, 1221.

Lightstone, A. and Evans, B. J. W. (1995). A new protocol for the optometric management of patients with reading difficulties.

Ophthal. Physiol. Opt., 15,507-12. Lightstone, A., Lightstone, T. and Wilkins,

A. (1999). Both coloured overlays and coloured lenses can improve reading fluency, but their optimal chromaticities differ. Ophthal. Physiol. Opt., 19, 279-85.

Mehta, A. M. and Derner, J. L. (1994). Magnetic resonance imaging of the superior oblique muscle in superior oblique myokymia. ]. Ped. Ophthal. Strab., 31, 37883.

Phillips, P. H. and Hunter, D. G. (1999). Evaluation of ocular torsion and principles of management. In: Clinical Strabis- mus Management, pp. 52-72. Saunders.

Plager, D. A. (1999). Superior oblique palsy and superior oblique myokymia.

In: Clinical Strabismus Management, pp. 219-29. Saunders.

Simons, K., Arnoldi, K. and Brown, M. H. (1994). Color dissociation artifacts in double Maddox rod cyolodeviation testing. Ophthalmology, 101. 1897-1901.

Spector, R. H. (1993). Vertical diplopia.

Surv. Ophthalmol., 38, 31-62.

Ukwade, M. T. and Bedell, H. E. (1992). Variation of congenital nystagmus with viewing distance. Optom. Vis. Sci., 69,

976-85.

von Noorden, G. K. (1996). Binocular Vision and Ocular Motility, 5th edn. Mosby.

Wilkins, A. J. (1995). Visual Stress. Oxford University Press.

Wilkins, A. J., Evans, B. J. W., Brown, J. et al. (1994). Double-masked placebocontrolled trial of precision spectral fil- ters in children who use coloured overlays. Ophthal. Physiol. Opt., 14, 36570.

There is one correct answer to each question

Chapter 1

1Which of the following could NOT be a symptom of decompensating heterophoria?

A closing one eye when reading B intermittent diplopia

C monocular diplopia D sensitivity to light

E intermittent blurring at distance

2The best way to assess vision in a pre-school child with suspected amblyopia is:

A Snellen chart

B Cambridge Crowding Cards C LogMAR charts

D Frook's cube

E single-letter Illiterate E test

3Which ofthese statements about the cover test is TRUE?

A speed is essential to maintain the patient's attention

B suppression is easily detected

C if there is no movement there is no heterophoria or squint

D it can distinguish between a squint and heterophoria

E use of the prism cover test utilizing trial case prisms held together is an accurate way to measure the phoria or squint angle

4Which of these statements about the near point of convergence (NPC) is FALSE?

A a near point of convergence of 8 ern is not acceptable

B sustained convergence at 15-20 ern is normal

C use a 6/9 equivalent letter and

repeat the measurement three times

Dconvergence can apparently fail if the near point of accommodation is poor

Eincreasing NPC on repeated testing suggests investigation for ill-sustained convergence may be required

5Which of the following is TRUE in relation to suppression?

A physiological suppression occurs

naturally

Bsuppression can vary in its intensity

Cvarious tests need to be employed to assess the depth of suppression

Dsuppression may be present in cases of high heterophoria

Eall of the above

6Which ofthe following is TRUE?

A eccentric fixation can be assessed using an ophthalmoscope and slit aperture

B standard notation is used for the classification of the position of fixation in eccentric fixation

C unharmonious ARC is considered to be an artefact of clinical testing

D three per cent of the population are stereo blind

E the speed of performing a stereo test is not related to the quality of stereopsis

Chapter 2

1Comitant eye deviations can be classified according to which of the following criteria?

A eye position and movement during

cover-test

Bfixation distance

Cprimary or secondary

Dlatent or manifest

Eall of the above

2Treatment for comitant eye deviations may involve:

A surgery

B refractive correction C vision training

D manipulation of the refractive correction

E all of the above

3A non-specific (basic) exophoria is:

A greater at near than distance B greater at distance than near.

C the same size at distance and near D variable with time

E difficult to manage

4Which ofthe following is the most appropriate term to describe an esotropia which occurs within the first 6 months of life?

A infantile B congenital

Cacquired

Daccommodative

Ecyclic

5A microtropia is:

A an eye deviation equal to or less

than 10° in size

Bmanifest

Coften associated with a latent component

Dassociated with peripheral stereopsis

Eall of the above

6A patient who demonstrates an increase in angle of greater than 10° base-in for near fixation with

+3.00 D lenses is best described as:

A malingering

B a fully accommodative esotrope

C exhibiting divergence-insufficiency