Acknowledgements: what follows is mainly the result of strabology teaching by the French doctor, Jean-Bernard Weiss, who disputed the idea that strabismus is caused by blocked nystagmus, at the time when it was the sole hypothesis in strabology, and who discovered the variability of strabismus and torsion, inventor of penalizations, of the Hess- Weiss test, of the Kratz torsiometer… and his research work continues.
This article takes particular account of French methods and organisation. Prevention and screening methods for amblyopia are currently stagnating. Systematic information to parents is necessary if further progress is to be made. The reverse of this stagnation, major progress has been made in terms of systematic screening for audiovisual problems in all French schools. The current efficient methods strongly resemble methods that have been available for many years and are yet under-used. There are three major ways by which to combat functional amblyopia:
- Prevention, that is to say screening and early treatment of risk factors
- Early screening and treatment of amblyopia itself
- Prevention of relapse up until the age of 12.
This can only be achieved with the massive help of paediatricians, general practitioners and school doctors, under the responsibility of ophthalmologists working exclusively with orthoptists. There is no question about this and full responsibility falls to these two professions. The role of opticians is also essential: producing good spectacles and offering advice regarding the best frames is their own special responsibility.
On the one hand there is an ophthalmological examination at the age of two months, for at-risk babies with specific risk factors. On the other hand is efficient treatment of the pathologies which cause amblyopia.
1.1 Examination at the age of two or three months for at-risk babies
1.1.1 Targeting at-risk babies
The importance of examining all babies could be argued. However the material impossibility of doing so means that there is no point in even discussing it. In case of a problem pregnancy (premature birth, foetal distress…..), obstetricians and paediatricians always remember to indicate to parents the need for early ophthalmological examination. On the other hand we ophthalmologists do not always remember to say to our at-risk patients that they should have their babies examined at the age of two months. Yet this information should be given to all those of our patients who have a hereditary risk or, even more importantly, to those who already have a child with this type of pathology: strabismus, nystagmus, amblyopia, strong ametropia (genetic proximity is closer between two siblings than it is between a parent and his/her child).
1.1.2 The ophthalmological examination at two months
This examination must be realistic and there is absolutely no question of referring to a "complete examination". Even less of reproaching an ophthalmologist who has missed a rare pathology that only a more indepth examination could have found.
The ophthalmological examination performed on a two month old baby comprises:
- a search for permanent or intermittent strabismus
- a study of ocular motility: is torticollis present, or pathological nystagmus or limitation of the ductions? (elevation is often difficult to obtain at this age, and the most efficient way of testing the ductions is to pick up the baby, make eye contact and then move the baby so that he moves his eyes in an automatic-reflex way)
- an explanation of the usefulness and importance for all babies of the alternated occlusion test, performed not by the practitioners but by the parents, regularly every two months,
- repeated instillation of tropicamide by the parents in the waiting room
- a retinoscopy, or retinoscopic control of an automated measurement
- examination of the fundus, ideally using indirect ophthalmoscopy, according to Schepens, in order to get a panoramic view of the fundus, showing the papilla and the macula as well as the whole of the retina. This reduces the risk of missing a coloboma, a scar or a retinoblastoma. The limitation of this method is that it can miss certain papillary hypoplasias, it is sometimes impossible, due to a misleading double contour, to identify the papillary hypoplasia, even when it is known to be present.
1.1.3 The conclusion of the two-months examination
If spectacles have been prescribed because permanent strabismus exists, or else ametropia well above physiological ametropia or clear anisometropia, the ophthalmologist must explain their aim (treating strabismus or nystagmus, avoiding anisometropic amblyopia, simply to enable the optical channels to reach full maturity….).
In case of even intermittent strabismus, the practitioner will remind parents of the need to place “signals” in the baby's field of vision, these should be contrasting motifs that the baby can see and placed such that the image seen by each eye will be very different if one of the two eyes is not looking in the same place. A magnificent all white or striped cot bumper, allowing the two eyes to capture the same image without looking in the same place acts like a sort of multiple choice and is used as an experimental way of encouraging strabismus, causing the brain to wander during the orthotropization period.
If a later check-up proves necessary, the ophthalmologist will remind parents that in case of any doubt regarding intermittent strabismus, they should bring in on a memory stick twenty front-facing photos taken with a flash (to obtain a corneal reflection) at different times, which will reduce the risk of missing intermittent strabismus.
Finally, it is helpful for parents to be able to access information and explanations and an increasing number of ophthalmologists are suggesting that parents should go to their website (strabisme.fr for the author) or that of one of their fellow practitioners.
2 Screening for amblyopia
“A baby who can see well can at least see well with one eye; it may be the case that he can see nothing with the other eye” (Fig.1). This is a phrase that should be communicated by paediatricians and ophthalmologists, if not by the media.
Fig. 1: “A baby who can see well can at least see well with one eye; it may be the case that he can see nothing with the other eye”
2.1. Systematic screening of all children at around the age of 9 months
Such screening is the object of another article in this issue, by Professor François Vital- Durand, author of the “baby vision” test (see also Points de Vue n°52/Spring 2005).
We would just mention that, whatever the results of this screening test, normal or not, it is still necessary to provide parents with common sense information, to insist on the importance of the alternated eye patch test, the need to consult urgently in case of any abnormality and the fact that all ophthalmologists will agree to see a baby with an abnormality within a relatively short time if details are given when the appointment is made.
2.2 The examination at two years
2.2.1 The ophthalmologist's examination
The examination performed by the ophthalmologist is the same as the one done at two months, except that it also includes presentation of the LANG test. When this test is positive we know that the child has binocular vision, and that each eye can see more or less well. When it is negative, no conclusion can be drawn.
2.2.2 Evaluation of acuity by parents
From this age, close visual acuity can be evaluated by parents and the ophthalmologist can complete his consultation by handing over a test sheet (without copyright), which is intended to get parents to evaluate visual acuity themselves, explaining that this evaluation must be done for a maximum of three minutes per day, over a period of several days, and should be systematically followed by a fun activity for the child. The successive stages are:
- teach the child to recognise and point to some of the drawings
- teach him to insist when the drawing is too small, so that his answer is clear, and this requires a certain amount of exuberance (“Well done!” “You are clever!”, etc.) and never say to the child that he's made a mistake: two years is an age at which children play only if they win every time
- start again, hiding one eye, showing only the easy drawings at least for the first two days of single-eye testing. (the “Transports” scale (Fig.2) given by the author to parents can be downloaded in PDF format from strabisme.fr. It can be distributed freely, but is not calibrated because its aim is above all to check on isoacuity and the development of acuity. Absolute visual acuity depends mainly on how good parents are at motivating their child).
Fig. 2: The buses are used to encourage the child and can be guessed more easily than the other drawings.
2.2.3 As from three years
Any lack of response to the Lang test or to the Weiss cat test is suspect.
It should be possible to measure visual acuity in the consulting room.
2.3 Screening at school
There is no question about its usefulness. Its main limitation is in hypermetropic children who are doing badly at school but who score 10/10 in the test, due to an accommodative effort that cannot be maintained for long.
3 Early treatment of functional amblyopia
We should increasingly use medicine based on proof, avoiding any return to the mystical ideas contained in certain publications which suggest the use of incorrect methods (treatment by acupuncture...).
Functional amblyopia is reversible, but only up to a certain age. The later the treatment and the more difficult it is: where optical correction would have been sufficient at the age of 3, extended wear of an eye patch will be necessary at 7. At the age of 8 or 9 even the extended wearing of an eye patch, which it is still recommended to try, will have much less of a chance of success and will generally be undertaken in vain if the child is any older.
There have been two major advances in the treatment of amblyopia: the extended wear of an eye patch and Weiss penalizations. Extended wear of an eye patch has been well assimilated. On the other hand, the immense majority of children having maintenance treatment for amblyopia are still asked to wear an eye patch intermittently, in cases where a penalization could (should) be used. That means every day “come on darling, it's time to put the patch on your eye”, when a voluntarily false optical correction in front of the dominant eye would be sufficient. In addition to this much greater comfort there is the interest of a convex over-correction in case of convergent strabismus (low estropia can become a near vision esophoria), and the small amount of surveillance required (savings and comfort for the parents) in the most frequent cases where an eye becomes the favourite for long vision and the other for near vision.
3.1 Anisometropic amblyopia
Treatment is principally the exact prescription of total correction. If this correction is prescribed at a relatively young age, it will in most cases be sufficient to heal the amblyopia, if the eye is normal in every other way.
If recuperation is not achieved, microstrabismus should be sought, which may have been missed with amblyopia which is also due to strabismus having been thought to have been solely due to anisometropia.
With regard to the question of wearing contact lenses or spectacles to correct strong myopia, the debate around aniseikonia is of little interest. The main thing for binocular vision, where present, is not to ceaselessly change the means of correction (and therefore of retinal correspondence). Moreover, contact lenses offer a better, larger image. They are the best solution when parents are able to manage them.
3.2 Strabic amblyopia
In cases of strong amblyopia, the benchmark treatment is wearing an eye patch stuck onto the skin. There are several ways of doing it but they must all follow a strict protocol. Prior to any patching of the eye, measurement and total correction of ametropia must be carried out.
In the absence of any amblyopia or in case of low level amblyopia, the choice of optical correction is a determining factor right from the very first correction. In cases where strabological dogma prescribes Total Optical Correction (the famous TOC), good sense would lead one to overcorrect the dominant eye by between +1 and +2, and this is for three reasons:
- penalizing this eye for distance vision means treating or preventing amblyopia, by forcing alternate use
- reducing near vision converging strabismus is good, at least from an aesthetic point of view
- reducing accommodation of the dominant eye often reveals hypermetropia that is higher than that initially estimated.
3.3 Organic amblyopia
All cases of organic amblyopia in children are functional to some degree and must be re-educated, with results that are sometimes amazing in the case of even very large scale retinal lesions, and more often disappointing in case of papillary abnormalities. However, in this latter case, there is often some degree of functional amblyopia to be treated.
4 Prevention of relapses
In the immense majority of cases, prevention of relapse should rely on slight penalization of the dominant eye up to the age of 12.
Conclusion: Progress required in five different ways
- Information: to ensure examination of all children in at-risk families from the age of two months.
- Use penalization instead of intermittent patches whenever possible (therefore in many cases), particularly when this is beneficial for strabismus.
- Develop baby-vision into a test that can be done at home by the parents; this means that it can be repeated, which will increase reliability (averaging out variability). Extensive distribution of interactive screens should have already led to the development of this type of test. For example, a screen with an alternating chequerboard pattern on a quarter side, either right or left. After a few seconds of presentation, the father or mother, hiding behind the screen, peeps out with a “boo” from the side on which the alternating chequerboard pattern is placed. If the child is looking at the right side before the parent pops out, it is considered that the chequerboard has been seen. The parent peeping out to say “boo” is not essential, but it does reinforce the test. The calibration question does have solutions, but the main thing is to be able to compare the two eyes and detect progress or regression.
- Amblyopia evaluated using visual acuity tests is only one facet in the evaluation of visual capacities. In 2012 no French ophthalmologist can ignore neurovisual disorders (almost 3% of all 6 to 11 year olds starting primary school), which are a curable factor in failure at school and distress.
- Bilateral amblyopia, whatever its cause, should benefit from a near vision addition, and the initial prescription for this addition in children should use bifocal lenses and not progressive lenses right from the start.