Subscribe to RSS
Emmetropisation: Sins of the mother?
For years I have made a conscious effort to discuss the importance of regular eye examinations for children. I have spent a significant amount of my clinical career within the hospital eye service, working closely with orthoptic departments and latterly have developed a specific interest in paediatric low vision.
So, when I received a letter from the school nurse recently stating that my 5 year old had ‘failed the most basic’ of the school ‘eye-tests’ I was rather taken aback. After a swift trip to my local friend and colleague to examine his eyes, my son came away with a rather smart blue frame and a big smile upon his face.
But what of emmetropisaton? If he were a mere -1.00 would it have been worth waiting a little longer?  But with his prescription being largely astigmatic, would he fall into this category?
What it did make me realise was that I know very little of the onset and progression of myopia and the vast amount of research in this area in recent years. Since I am off to Optrafair at the weekend, perhaps I shall buy a book and read around the subject. Not only will it fill an educational void, but it may make me feel slightly better as a parent who had largely ignored her own advice on the importance of regular eye examinations for young children.
Off to the dentist next.
Robert Petrarca // Apr 19, 2007 at 2:19 pm
Don’t worry Jane, it is known that a significant proportion of infants show hyperopia of more than +3.50 DS.
Emmetropisation
Refraction error in infants is usually hyperopic, and generally develops toward emmetropia during the first years of life. However, the mechanisms that regulate human ocular development are poorly understood. In particular, the extent to which accommodation induced by lenses may affect this process have not been discovered. To date, there have been few, if any studies investigating human emmetropisation in infants and comparing the impact of refractive correction.
Studies of animals have though proposed that ocular development and refraction are partly regulated by visual feedback related to optical blur, the implications of these effects on the practice of refractive correction in infancy and early childhood are not yet fully understood.
Finally, it should be noted that the partial refractive correction of infants with hyperopia has the beneficial effects of reducing the incidences of strabismus and poor acuity. Therefore partial correction of refractive error is certainly of benefit, and is believed to achieve these results without impeding the normal developmental regulation of eye growth and refraction.
Jane Macnaughton // Apr 27, 2007 at 12:53 am
Thank you Robert.
At 18 months he was +150/-3.50 x V pretty much equally in both eyes. Today, aged 5 he has come down to Plano/-1.25 x V, again equally in both eyes. His VA’s are 6/9 (although only just) and his stereoacuity (TNO) is 60″
We have indeed been watching him and have decided at this stage to prescribe. Having said that I did not realise how difficult it would be to get him to actually wear them!
Given the level of streoacuity, would I expect a better outcome of VA?
Simon Frackiewicz // Apr 28, 2007 at 2:33 pm
Hi Jane,
Having looked through all the literature I can find, there is little that mentions the changes in astigmatism with age as most papers focus (pardon the pun!) on mean refractive error. There is no doubt that your son’s prescription is tending towards emmetropia, and a 1.25 dioptre cyl at this age is still what I would class as borderline for prescribing. To see 6/9 (assuming linear test) at this age is what I would consider normal, and was used as a cut-off for referral in most vision screening programmes I was involved in as an orthoptist. Bear in mind that his visual system is still maturing and will continue to do so for the next couple of years. The fact he is not mad keen on wearing his specs also confirms the borderline nature of his prescription as in my experience, kids who need specs to see more clearly will wear them without a fuss.
As regards the question about stereoacuity vs. distance linear acuity, I would have said that the two correlate quite well at the moment, i.e. I would expect 6/9 vision in either eye to give 60� arc. It is possible that there may be an element of meridional amblyopia which, now the astigmatism is corrected, should give rise to a further increase in linear acuity, and possibly stereoacuity too.
As an orthoptist, I would encounter this scenario on a daily basis, and in most cases acuity improved both with and without specs after a few months of wearing them. I can imagine this came as a shock, but I suppose it has been a useful exercise in seeing the system from the point of view of a parent rather than practitioner.
Simon
Leave a Comment