This is the second of four articles where you can decide on the best strategy when presented with different binocular vision challenges Your quest continues. Do you accept a second challenge to help you enlighten your knowledge on binocular vision? Do you have the skills and courage to solve your patient’s problems and create a loyal patient for life…take the test now!

YOUR CHALLENGE
A 10-year-old boy attends with his mother for his first eye examination in your practice. The family have recently moved to the UK from China. There are no concerns with his vision, and he has never had an eye examination and never been seen at the hospital eye clinic. He likes to play computer games and enjoys football.
His general health is good and he is not on any medication. He had been born two weeks early but had a normal delivery. Both his parents wear spectacles (myopic) but there is no known ocular diseases.

LOOK WHERE YOU’RE GOING – SUBJECTS IN THIS SERIES
• Part 1 – asthenopia
• Part 2 – unilateral reduced acuity
• Part 3 – diplopia
• Part 4 – cosmetic appearance

Walkthrough
For each step of the process, decide on the option you wish to take. Then go to the step indicated. When you make the correct choice, you will be helped towards the next step. Once you have completed the challenge it should become clear which is the most systematic approach to investigate the child with reduced vision in one eye.

STEP 1 You check visions with crowded logMAR letters. He reads
R 6/6 L 6/36.

What do you do next?
a) do pinhole – go to 2
b) check near vision – go to 3

STEP 2 You hand the boy the pinhole and he now reads R6/6 L 6/36. This makes you suspect that refraction is not the only
cause of his reduced left vision.
Go to 4

STEP 3 By checking the near vision, you gain information about what sort of refraction he may have (eg myopia would give good near vision). His near visions are R N5 L N12. So you suspect he is
not myopic. You decide to check with a pinhole too. Go to 2

FIGURE 1 Retinoscopy on a young child

STEP 4 You decide to check cover test and motility which are normal. You wish to check his refraction. Do you;
a) do retinoscopy (Figure 1) and subjective? – go to 6
b) decide on a cycloplegic refraction? – go to 5

STEP 5 It would be useful for his age group to see what the best corrected visual acuity is subjectively.
Go to 6

STEP 6 His retinoscopy and subjective refraction is;

R +1.00DS (6/5)
L+3.00/-1.00 x 90 (6/24).

What other tests would you do to check the end point?

a) +1.00 blur – go to 7
b) amplitudes of accommodation – go to 8

STEP 7 The +1.00 blur test reveals R 6/15 L 6/36. This makes you suspect the left eye is under corrected. After discussing this with his mum,
you decide to do a cycloplegic refraction.
Go to 9

STEP 8 You pick up the RAF ruler and measure monocular amplitudes.
Your findings are R 14D L 12D but he is looking around the room and losing concentration. There are probably quicker ways to check under correction during the refraction. You decide you need to do a cycloplegic refraction.
Go to 9

STEP 9 Which choice of drug would you use for this child who has dark brown irises? You look in the cupboard and have a choice of
a) 0.5% cyclopentolate – go to 10
b) 1.0% cyclopentolate – go to 11
c) 0.5% tropicamide – go to 10

STEP 10 You wait 10 minutes and find no pupil dilation, and remember with darker irises you should use a stronger concentration of cyclopentolate.
You instil 1.0% cyclopentolate.
Go to 11

STEP 11 You tell the patient to wait outside for 30 minutes and check for cycloplegia. How do you check this?

a) Look at pupil dilation – go to 12 or
b) Look for the retinoscopy reflex fluctuating when you ask the patient to look at distance and then near – go to 13
c) Measure amplitudes of accommodation on the RAF ruler – go to 14

STEP 12 Even though the pupils are dilated, this does not mean that the accommodation is completely arrested. You notice the retinoscopy reflex still fluctuating when asking him to fixate on the distance target and then your retinoscope light. You wait another 10 minutes and check again and find that by allowing a bit more time, his reflex is stable. You are satisfied his accommodation is arrested.
Go to 15

STEP 13 The reflex still changes so you wait 10 minutes before he has reached cycloplegia.
Go to 15

STEP 14 You pop a trial frame on with some +4.00DS spheres and measure he still has three dioptres of accommodation. You recheck again 10 minutes later and his accommodation is now near zero.
Go to 15

STEP 15 The resulting cycloplegic refraction is;

R +1.50 DS (6/6)
L +4.25/-1.00 x 90 (6/24)

Ophthalmoscopy is normal.
You explain that he has anisometropic amblyopia.
What is your management of this patient?

a) Prescribe full prescription for full time use – go to 16
b) Prescribe reduced prescription ( R+1.00Ds L +3.75/-1.00x 90) for full time use – go to 17
c) Prescribe reduced Rx and refer routinely for orthoptic assessment via GP – go to 18

STEP 16 He returns after 1 week of wearing the spectacles but his mum says he is reluctant to wear them except when doing his homework or playing on the computer. In class the board seems blurred. Since his ocular motor balance is not esophoric you try the reduced Rx.
Go to 17

STEP 17 You see him in two months and his mum reports he has been wearing his glasses well. His VAs are R 6/5 and L 6/18. You continue to monitor his VA in three months. His eventual VA is R6/5 L 6/12 with no change on subsequent visits.
Do you;
a) suggest occlusion? – go to 19
b) explain this would be the best vision he can achieve as he is over the age of the critical period and put him on routine six-month checks from now on?
– go to 20

STEP 18 In the absence of strabismus or pathology, amblyopia could be managed in practice. You decide to prescribe the reduced Rx and read up on amblyopia treatment.
Go to 17

STEP 19 You start on a programme of occlusion of the right eye for two hours per day and monitor in one month. You continue to monitor at sixweekly intervals thereafter and stop occlusion when the left VA has not improved on subsequent visits beyond 6/9. You all agree that you are happy to stop the treatment. You review the patient at three to sixmonthly intervals. Patient and mum are grateful for all your time and effort.

STEP 20 Some schools of thought suggest that even older children can benefit from occlusion. Mum is keen. You decide to refer this patient for routine orthoptic assessment for occlusion therapy. Patient and mum are grateful for your time. (See below on treatment for amblyopia).

You have completed this level. Congratulations!

FIGURE 2 logMAR charts with letters (a) or symbols (b)


DIFFERENTIAL DIAGNOSIS OF REDUCED MONOCULAR VISION AND VISUAL ACUITY (VA)
Measuring visual acuity is usually performed as the first clinical test after taking a history and symptoms. The presence of reduced vision or VA will lead the practitioner to find the cause of this and potentially correct it with any associated binocular vision anomaly. Before we consider the possible causes, we can also check several tests that will give us some clues immediately.

CROWDING EFFECT
Snellen acuity or logMAR acuity will give us a baseline measurement which is universally recognised. Letters on a conventional Snellen chart will be presented in crowded lines. This can be difficult with younger children although pointing could be used. LogMAR charts (Figure 2) have the advantage of equal spacing
between letters and lines, equal number of letters per line, as well as letters of equal legibility. They are considered to be more consistent and repeatable, and take into account letters missed or read on the next line. Monitoring changes in VA (for example with the introduction of treatment of amblyopia or monitoring a
progression in pathology) is considered more reliable compared to Snellen.
Computerised or projection systems allow single line or letter presentation of both Snellen and logMAR charts. This can aid younger children or those who cannot cope with multiple lines. The use of the ‘box’ around the line of letters contributes to the crowding effect (Figure 3). Measuring vision without the crowding effect, either as single lines or single letters, also gives clues to the cause of reduced vision. If the vision with and without crowding is the same, it is likely to be pathology or refractive error. If there is an improvement on uncrowded letters, we should suspect amblyopia as there is contour interaction between the central letter and its surrounding letters, which interferes most at the fovea.

PINHOLE
Another quick but important test is the use of the pinhole, where the vision improves if the cause is refractive error. This reduces the blur induced and, in the absence of central media opacity and macular pathology, should result in a vision close to the best corrected VA. Pitfalls include a pinhole being too large, lack of
understanding of the test, and difficulty in using it due to head or hand tremor or an abnormal head posture. Amblyopes would show no improvement with a pinhole.

OCCLUDER USED
The type of occluder chosen should not influence too greatly the measured vision, although it should be ensured that full occlusion takes place as some patients will naturally try and peep around the occluder, especially if the eye with better acuity is being covered. The use of the patient’s hand is not recommended to
ensure they are not looking through gaps between their fingers (Figure 4).
For younger children, specially designed frames with flip down occluder lids can prove useful (Figure 5). If allowing the patient to hold an occluder, remind them not to press on the eye as this can result in a compressed cornea leading to a temporary blur and drop in vision.

FIGURE 3 Boxed letter on electronic display

POSSIBLE CAUSES OF REDUCED VA
a) Refractive error
b) Ocular pathology
c) Amblyopia
d) Malingering / non-organic causes
a) Refractive error

This is probably the most common cause of reduced vision that optometrists will encounter and to eliminate as a cause. It may also be associated with amblyopia which will be discussed in the section below.

Tests required:
• Retinoscopy is always advised especially on new patients or children at any visit and on patients where there has been a change in the vision or VA. It gives an objective result (useful in malingerers) and also allows a view of the ocular media including corneal ectasia, lens opacities and vitreous opacities/haemorrhage.
• Subjective refraction should be attempted and, in this case, a 10-year-old should be reliable. As the patient did not blur back significantly with the +1.00 test, this would indicate latent hypermetropia and hence the need for the cycloplegic refraction.

FIGURE 5 Two occluder frames for children

FIGURE 4 Use of the hand for occlusion is not recommended

Management: If a refractive error is found that improves VA to a normal level, the management is to consider prescribing. This would depend on the age of the patient, whether there were symptoms and any difficulties with adaptation to anisometropia.
In the case above it would still be useful to prescribe the prescription for full time wear to begin treatment for amblyopia.
Had the left VA been normal with the correction, and he is asymptomatic without spectacles, what benefit would his correction give him? Having bilateral good VA would improve stereopsis and aid fine motor skills, so it could be beneficial for more active pursuits, eg sport. It can also be more comfortable for concentrating tasks, such as prolonged reading. With the adaptation for significant anisometropia, there would be adaptation anomalies where spectacle magnification in the left eye would make it difficult to maintain binocular single vision. A contact lens could be used but not without parent and patient motivation.

Would a partial correction be of any use to aid adaptation? Generally, when prescribing for anisometropia, it is recommended that the difference between the two eyes is maintained in order for binocular accommodative effort to be the same. For example, in this case, you would take the result R +1.50 DS and L+4.25/-1.00 x 90 and reduce it by 1.50D in both eyes, prescribing R plano and L +2.75/-1.00 x 90. In any cases where the Rx is being adjusted, the ocular motor balance must be considered too. If this boy had any esophoria or tropia, we would aim to give maximum plus to reduce any accommodation and accommodative convergence. For exo deviations it would be beneficial to reduce the plus power to aid control.

b) Ocular pathology This would be ruled out examining the eyes and visual pathway. Any media opacities, macular disease, or neurological causes
should be investigated.
Tests required:
• Slit lamp microscopy
• Fundus examination
• Intraocular pressures (might be considered)
• Field of vision testing

Management: Active pathology needs to be referred. Long standing pathology should be accurately recorded for monitoring.

c) Amblyopia
This is characterised by reduced VA in one eye (or rarely both eyes) in the absence of any pathology and is not correctable by refraction. Amblyopia is caused by some form of deprivation during the critical period, usually assumed to be from birth up to the age of eight. This can be;
• Uncorrected refractive error
• Disruption in binocular function, eg strabismus
• Complete stimulus deprivation, such as in ptosis or media opacity.

Refractive amblyopia can be bilateral in high bilateral ametropia or meridional in cases of high astigmatism (worse with uncorrected oblique cylinder axes). Ansiometropia is often the cause of unilateral refractive amblyopia. Recent reviews show that as little as 1 dioptre of hypermetropic anisometropia can
induce amblyopia whereas, in myopia, 2 dioptres or more (since near vision may be stimulated in the more myopia eye). In astigmatism, 1.5 dioptres can induce meridional amblyopia.
Tests required: To investigate the causes of amblyopia:
• Refraction (including cycloplegic refraction)
• Cover test to look for strabismus
• Anterior and posterior eye examination.

In this case, the only significant finding is the anisometropia.

Management: Treatment of amblyopia by optometrists depends on the possible underlying cause. It would be advisable for most cases of children with strabismic, mixed (strabismic and anisometropic) and stimulus deprivation amblyopia to be referred for ophthalmological assessment and treatment. Microtropia is a case where there is anisometropia and suppression and it can often present with similar characteristics to pure anisometropic amblyopia. The angle of strabismus is small and easily missed and should be considered in anisometropic amblyopes that do not respond to occlusion. The four prism base out test and eccentric fixation tests are useful for testing for this.
Pure anisometropic amblyopia could be managed by optometrists in practice with success. The main points in this scenario to consider before managing amblyopia, and specifically anisometropic amblyopia, are;
1 What is in the best interests of the patient?
2 Have you got the time and expertise? Would you treat this 10-year-old? He is over the well-known critical period of eight years of age where treatment of amblyopia
is considered unlikely to work. The most recent research shows that even adults up to the age of 40 can gain some improvement of VA in an amblyopic eye, although the gains are not as great when compared to the treatment of younger age groups. In this case, a previously untreated 10-year-old would be worth a go. The patient would always benefit from having better VA, and potentially increased binocularity (including better stereopsis). It could affect his future career choices, leisure activities and the risk of going blind (if the good eye was ever compromised). However, there is the inconvenience of the treatment and issues with compliance to consider. Agreement with and co-operation from the patient and parent would generally improve success rates. Also, it should be considered whether they would prefer to being treated in your practice or under the hospital eye service.
For the practitioner, it is really important to consider if they have the time to monitor these patients appropriately for the treatment to work. They will require ongoing chair time. Who is going to pay for this (NHS or private)? If this is not feasible then it is better for the patient to be referred to the hospital eye clinic. However, the author would encourage readers to be involved in occlusion in the cases of straightforward refractive amblyopia. It is often successful, is usually more convenient for the patient, increases your reputation (hopefully) and reduces the burden on the NHS secondary centre leaving resources for them to treat the more complex amblyopes.

Sequence of treatment:
1) Correct refractive error – Consider ocular motor balance, adaptation. Advise constant wear. In refractive amblyopia (ie without strabismus), monitor every six weeks and, if there is improvement in VA, continue. If VA stabilises consider occlusion.
2) Occlusion therapy – How long to occlude? What do you use? In children, one to two hours’ occlusion of the better eye per day is advised, ideally while the child undertakes detailed visual tasks. Commercially available plasters over the eye or fabric patches over the glasses are readily available. Monitor in six to eight
weeks. Maximum improvement should be seen in the first six weeks, then checked again at 12 weeks after which there is limited likelihood of further improvement. What do you do if VA begins to drop again? You could resume occlusion for maintenance, but would need to monitor closely.
3) When to refer? – if no improvement in VA, even after occlusion, or the level of VA achieved does not match the level of anisometropia, eg small amounts. Rule out microtropia. Also refer if patients prefer HES, or you feel compliance may be better due to time constraints in general practice. Those with poor compliance with patching may benefit from atropine penalisation. It has the advantage of being more cosmetically acceptable, but some systemic side effects are possible. This normally needs a prescription from a doctor so would be better managed at the secondary care centre.
4) Which groups of patients do you need to be wary of? Although older children and adults can be treated, the neural plasticity will be reduced. In those with strabismic amblyopia (including undetected microtropia), this means that sensory adaptations may not take place and intervention could lead to intractable diplopia. Those who do not show improvement (especially children who have never been seen by the hospital eye service) should also be referred as should those for whom you
have a strong suspicion of any other pathology. Patients who have previously been treated with occlusion often do not show the improvement expected.
d) Malingering and non-organic causes Occasionally one may encounter patients where there is no obvious identifiable cause for the reduced vision (no refractive error, strabismus or pathology). Malingering might then be considered.

Tests required:
• Careful refraction including fogging techniques
• Polaroid filters
• +1.00 blur tests
• Change of working distance to the letter chart
• Cycloplegic refraction to convince you there is no significant or change in their refractive error
• Ocular and neurological examination such as ophthalmoscopy and fields testing.

Management: Unexplained reduced VA should be referred to the GP. You can always annotate that you could find no cause of this but make your suspicions as to a possible cause known. This may include the fact that a baby brother has just been born, significant stress at school or work, or that a best friend has just got
glasses. This will help the doctor gauge with what urgency to refer them onto the HES.

SUMMARY
Anisometropic amblyopia is often seen in the primary care setting. A cycloplegic and subjective refraction should be performed and the resulting correction prescribed for full time wear. Treatment for amblyopia is effective in patients before the age of seven years. It can still be considered in older patients up to their late teens, although in older age groups be wary of causing intractable diplopia. If improvement in the VA is found with wearing a correction, continue to monitor until any improvement tails off. Occlusion can be done in practice if the practitioner has the time to monitor these cases. One to two hours a day is considered effective in most cases, but can be increased to up six hours. Refer any cases where there is no improvement or any unusual circumstances. If deciding to refer a patient for occlusion, always prescribe any refractive error found to give them some visual benefit while they are waiting for their hospital appointment.•
Sosena TW Tang is an optometrist based at Aves Optometrists in Ware and the QEII Hospital, East and North Herts NHS trust, and is a College of Optometrists assessor.

USEFUL READING
Newsham, D and Meritxell, C A, 2011, Recent advances in the management of amblyopia. Optometry in Practice, vol 12, issue 3.