The genesis and epigenesis of vision
Two months after my parents enjoyed a passionate embrace, which resulted in an embryo, my genes decided to release, from what was going to become my brain, a protuberance which hit up against the external membrane of the embryo. This was when a series of complex tissues was formed, retina, optical media, crystalline and cornea, all carefully laid within an optical cupule. It was only after five months, once my sex was well defined, that this organ enabled me to turn away from unpleasant light in the narrow space I had been granted. When my mother undressed on the beach I wriggled as much as I could to escape from the light. I was already photophobic. I remained so for a long time after I went down a slide that took me through into dazzling surgical light in the midst of the exhausted cries of my mother and the panic of my father, overcome with emotion.
I was the object of great care, my cord was cut and clamped and I was set adrift in a new world in which I was encased in fibres that felt rougher than the soft amniotic liquid I had been used to floating around in, although things had got a bit tight just recently.
I could see there, as long as the strong lights that bathed the surroundings were turned off. I sought with my nose and mouth and could see a round mark on a big nipple from which flowed nectar that I cried for every time I awoke. I hung on to this nipple, just as I hung on to the eyes in the middle of my mother's face. I even hung on to her finger, as if to secure my hold on the world.
As soon as my father and my elders came over to see me I could activate old reflexes to imitate their useless mimics. I pulled out my tongue, opened my mouth, pouted - and they though all this was hilarious.
They came to check that my pupils were good and dark, that my eyelids were in place and my eyes properly formed. A wise man even came to show my parents that I could follow a large target, which moved very slowly from right to left and that I systematically looked at the motif on an acuity card. He observed in my dilated pupils the mass reflection of a small light to check that my retinas were perfect and on the clarity of the transparent media.
Fig. 1: Portable slit lamp (photo: V. Jobert).
After eight days I was able to recognise my mother's face, even though it was very similar to that of her sister. But the people around me still thought I couldn't see a thing. They cuddled me, cradled me, sucked my cheeks, inundating me with their scents and smells. I quickly learned to identify who was carrying me around. To tell the truth smells reassured me more than my vision of what was happening.
It was towards the end of the second month that I made a major discovery, the social smile. As soon as my mother brought her face close to mine I got all my facial muscles moving and triggered the same reaction in her face, together with giggling and blushing - what wonderful emotion! I organised my response by ranking the contractions of the relevant muscles and throughout my life I intend to use my smile to seduce whoever and whatever comes my way. Later I learned that my prefrontal cortex has an area of mirror neurons which enables me to imitate the mimics and gestures of my interlocutor.
When I was four months old I could move my hands at will, that was a new toy I never got tired of. I caught hold of the trinkets dangled in front of my eyes, took them carefully between finger and thumb with the utmost precision because I could see in relief. It was difficult and a bit touch and go at first, but it got easier and easier. From then on the two tenths of my vision enabled me to recognise the objects around me. They had a very strange quality, colour, which I had no idea what to do with for several months more. Soon I was able to distinguish the food I was given; they introduced me to vegetables and biscuits and to all sorts of fruit and sugary preparations. The spatial revolution happened towards the seventh month. I could sit up, the world opened up in every direction but it took me two months before I could coordinate my limbs and crawl. By that time I could see well. I understood spoken directions and turned round to look at my mother when I was called. I couldn't speak but I understood what my parents wanted. By the time my birthday came around I had 4/10 vision. I stood up and soon I could walk. My hypermetropia lessened but I was focusing up to a few centimetres from my eyes. My field of vision was complete but I had to learn to use it. My vision was still fragile, but all its components were present and I would soon be using it for walking. It was just a question of waiting.
What’s the current position?
The clinical approach, a plea for screening.
The essential elements in the visual function (optics of the eyeball, acuity, ocular alignment, processing by the cerebral cortex) undergo most of their maturity process over the course of the first year of life, characterised by a period sensitive to the influences of the signal quality. This is a good time in which to examine for abnormalities and make up for defects in order to limit, or even prevent, their unfortunate consequences. In France ever since 1995, the carnet de santé (child's health record) has recommended regular monitoring of visual capacity and particularly an examination during the ninth month. This article will attempt to detail the method used for this examination and justify the grounds for it.
Before the age of one
In the days following birth, doctors test for malformations, check on the clarity of the optical media, on the fixing and following of a contrasting object. Over the course of the next few months, doctors check on ocular alignment and the child's visual awakening. It is more difficult to detect congenital glaucoma but any trace of cataract must not escape his vigilance. Any sign of malformation or visual disability is, of course, addressed as soon as it is suspected, to identify the diagnosis, prepare the parents for work on living without good vision if the diagnosis is poor and set up specialised education that can begin around the fourth month. In the case of strabismus, it is not the paediatrician's responsibility to detail the diagnosis, but it is his responsibility to send any doubtful cases to see an ophthalmologist as from four months old, although the ophthalmologist will not begin any treatment immediately. This article refers more particularly to the test performed at 9 months on children who appear to have no problems at all. This particular test can of course be performed at any preverbal age, with appropriate adaptation.
Fig. 2: From 7-8 months old, a child turns round when instructed and is shown the patch on the eye of the parent holding her, before the patch is placed on her own eye.
The test performed at 9 months
The child's health record makes regular mention of surveillance of good visual development and the examination for strabismus during the first few years of life. However no details are given as to exactly which tests should be carried out, and there is resounding silence with regard to refraction. The reason why the 9th month is chosen will be explained. An examination is recommended if there is the slightest doubt. Time scales are important and the orthoptist will be able to differentiate between epicanthus, the large eyelids that give rise to a suspicion of strabismus and cases that require an in-depth examination. In many countries, the optometrist will take charge of the first phase of screening and begin treatment, with any necessary surgery performed by the ophthalmologist.
The baby vision appointment
The appointment includes three stages which are all almost as important as each other.
1-The orthoptic examination
The search for strabismus uses a test on screen with screening glasses (Sarniguet-Badoche). The test looks for oculomotor abnormalities (convergence) and checks on pupil reaction and stereoscopic vision.
Clinically, the easiest way to evaluate relief vision is to use a stereogram with random points. It is practical because it does not include any monocular index and does not require the wearing of special spectacles. About the size of a postcard, the test is presented in a fixed position, after the examiner has shown the child the card and allowed him to touch it.
The Lang or Bébé Vision Tropique test card can be used as from 6 months. The probability of success increases with age. At 9 months, 60% of children give a positive response. However experience shows that if a child does not respond positively this may also mean that he has not understood the stereogram game or refuses to point. Consequently only positive responses are taken into account; they mean that constant strabismus and amblyopia can be eliminated.
Measurement of spatial resolution, or acuity, is part of the orthoptic test, in the same way as with adults. It has become accessible in clinics thanks to Acuity Cards, using the technique of preferential vision. The test includes a series of cards printed with increasingly fine pictures, located towards one of the extremities of the card. The cards are presented to the child without the experimenter knowing on what side of the card the motif is positioned. The examiner discovers on which side the pictures are located by observing the direction of the baby's eye movements and his fixing through a small hole located in the middle of the card. A trained examiner can measure binocular and monocular resolution in just 6 minutes in a child with no particular problem. This examination is easy to perform after the age of 3 months. It is very easy at around 9 months and more difficult after 12 months.
Acuity measurement results are shown in Table 1. They indicate that babies can see better than was thought. Development of acuity is regular over the course of the first year, before slowing down, achieving 10/10 at around the age of 5 years, with acuity levelling off at around 13/10 at about the age of 10.
Tab. 1: Development of spatial resolution (acuity) measured with acuity cards.
This examination becomes particularly useful in the case of amblyopia, because it enables dosage of the occlusion regime and monitoring of recuperation, as well as in the case of low vision to direct specialised education.
2- Refraction test
Defective refraction means a major risk of strabismus and amblyopia, particularly anisometropia. Unfortunately, ametropia is not accompanied by any warning sign and only disturbs a child's behaviour in extreme cases. The use of skiascopy (or objective refraction) is difficult. The practice is now very uncommon, even amongst those ophthalmologists who have an autorefractometer that can be used from the youngest age, but which is less reliable than a good skiascopy. During the first year, cycloplegia is performed with tropicamide (Mydriaticum), three drops with at least a 5 minute interval, examination 20 minutes later. This is very useful for screening for ametropia and will be prescribed after refraction with atropine or Skiacol®. Cyclopentolate 0.5% (Skiacol®), with a 50 minutes waiting time, is officially counter-indicated in France (but not elsewhere!). Children with strabismus are systematically examined under atropine.
Fig. 3: Plusoptix autorefractometer (photo: V. Jobert).
Fig. 4: Skiascopy.
3- Fundus examination
There is no question about the usefulness of a fundus examination. The examination should always be done using indirect retinoscopy or with a Layden glass or with three mirrors in order to check on the periphery. Unfortunately this is rarely the case. The fundus examination is particularly interesting to eliminate the effects of retinopathy in premature babies, search for any damage from toxoplasmosis, papilla paleness, malformations, etc.
Fig. 5: Indirect ophthalmoscopy (photo: V. Jobert).
Who should be examined?
No study of the geographical population has been done to define the proportion of babies with visual deficiencies (the definition of which is arbitrary). By considering a variety of data it can be stated that one child in every 5 (20%) presents a symptom that should be followed up. Of these, there is one false positive with a symptom that will correct itself (epicanthus). 12% remain therefore, half of which are functional genes (astigmatism) which will have consequences only as from nursery school age. The remaining 6% have a high risk of strabismus, amblyopia or severe functional gene (myopia, excessive hypermetropia).
It is therefore reasonable to give priority to testing of the most high-risk populations which include premature babies (<1500g), difficult births, visual heredity, neurological problems, ptosis, toxoplasmosis and, of course, babies with symptoms.
What about all the others? Although the probability of discovering a problem is low, the probability of it being discovered through screening is absolutely nil unless systematic testing is performed. Is it reasonable to offer such testing? That all depends on the public health policy.
Why at 9 months?
At this age the test is more reliable than if done any younger (when fixing is less precise) or later (the child is less cooperative).
At 9 months old, a child is at the peak of the period of plasticity of the visual system. If occlusion is prescribed over a limited time it will be very efficient and well accepted. If the child already suffers from amblyopia, it will not be very deep and the child will accept the occlusion into his bodily schema which is still adaptable, and spectacles too, if they are fitted correctly.
Who performs the examination?
This paragraph, which is the author's opinion only, may be seen as controversial. It takes into account the extremely varied situations found in the various regions of France, which are more or less well endowed with ophthalmologists and orthoptists trained in measuring refraction, as authorised by their professional certificates. This problem does not arise in countries where optometrists perform all the tests.
The test described above is practised in France under the responsibility of an ophthalmologist who may delegate the search for strabismus and acuity and refraction measurement to an orthoptist. In some areas where there are only very few ophthalmologists or when the time lapses for appointments are unreasonable, the paediatrician or GP will send the child to an orthoptist who will perform an orthoptic examination and, in the best of cases, a refraction test too. In these latter cases, only children screened as having the pathology will be sent to an ophthalmologist for a further visit. These tasks are carried out by optometrists in many countries. Orthoptists are now authorised to perform a refraction test, which requires cycloplegia. But this cycloplegia must be prescribed by a doctor, which restricts its performance dramatically, unless the orthoptist works in immediate proximity to a doctor. This recent development would simplify the procedure and significant savings could be made if the practice were to be generalised. The arrival on the market of paediatric autorefractors used to screen for refraction defects is making screening for ametropia easier. However, the data from these devices is not yet as reliable as that obtained by skiascopy. We dream of apparatus that could enable us to carry out a refraction test without the need for cycloplegia. But we will have to be patient…
Fig. 6: SureSight autorefractometer.
The paediatrician’s role
He monitors the clarity of the optic media and ophthalmological pathologies. He tries to identify epicanthus and refers cases of strabismus from the fourth month. With regard to amblyopia, he can use the screening glasses and perform the test on screen if he is trained to do so. Some use the acuity cards and the Lang card (stereoscopy). So much the better because this series of tests will screen for some of the pathologies concerned. However paediatricians do not have the means by which to screen for refraction defects, which is the main cause of amblyopia, and therefore run the risk of wrongly reassuring parents.
Risks linked to personal and family history are still, therefore, a good indication for paying a visit to the ophthalmologist, optometrist or orthoptist.
Fig. 7: Rétinomax K-Plus2 autorefractometer.
The optician’s role
He cannot be satisfied with just decorating the face. With babies and children he takes on a teaching role and must convince parents to cooperate with the technical demands of their child wearing spectacles, which are essential treatment in the good development of visual function. It is wonderful to see opticians training in the use of spectacles for tiny children. An increasing number of them have understood that fashion comes after technical considerations. These spectacles have to be as strong as possible, must not distort (we hate metal), not dangerous if impacted and must go up as high as the eyebrows but without touching the cheekbones. And, just to add yet more difficulty, the spectacles must have a bridge adapted to the child's nose, one that doesn't slip. Quite a challenge isn't it? Harry Potter did a great service by popularising spectacles with large lenses. It's good to see specialist children's shops opening and an increasing number of sales outlets with a children's sector. Bravo!
Early visual testing and the therapeutic methods that are easily applied at this age can be used to prevent almost all cases of amblyopia and a large proportion of strabismus cases, for which the number of surgical operations has been dramatically reduced. Children showing symptoms can be tested and can receive treatment after the 4th month. It would be ideal to perform this test on all children around the age of 9 months, to screen for and prevent amblyopia and strabismus. Paediatricians and GPs are now extremely aware of these problems and refer cases to orthoptists or optometrists who deal with the first phase of screening in areas where ophthalmologists are unavailable. However it is still relatively infrequent to see children being tested before the age of one. The practice of performing an early refraction test is spreading and we would like to see it becoming general practice. The availability of paediatric autorefractometers has indeed revolutionised these tests.
The visual function continues to develop until after the age of 5. However, it is during the course of the first year that children develop the control and mental representation of their body in external space. It is never too early to encourage the best possible usage of existing capacities.