Jordy S. Steltman and Huib J. Simonsz

Host: Prof. dr. Chris de Zeeuw Cerebellar Coordination & Cognition.

The Guest Speakers:
Jordy S. Steltman and Huib J. Simonsz, Dept. of Ophthalmology Erasmus University Medical Center, Rotterdam.

Title: Baseline findings in the Early Glasses Study indicate that amblyopia might cause anisometropia, opposite to what is commonly thought.

Abstract:

It is common knowledge that amblyopia (prevalence 3-3.5%) is caused by esotropia (squint towards the nose), by refractive errors or, rarely, by deprivation. Refractive errors are (i) bilateral hypermetropia (need for + glasses), (ii) astigmatism (need for cylinder glasses) or (iii) anisometropia (>1.5 dioptres left-right difference in refractive strength). Screening for these refractive errors and prescription of early glasses, in an effort to prevent the development of amblyopia, was introduced in Flanders, Belgium for all children in 2012. Before refractive screening at age 1 and 2 is implemented in all 870 ‘Consultatiebureaus’ in the Netherlands and early glasses are prescribed to 16,000 children annually, its effectiveness and cost-effectiveness are examined in our Early Glasses Study: 601 children are followed until age 4 after an eye examination at the age of 14 months, and the 10% of children with high refractive errors have been randomised into wearing glasses or not. The Early Glasses Study and its baseline findings (doi: 10.1007/s00417-024-06621-8) will be explained by PhD student and ophthalmologist in training Jordy Steltman.

Contrary to expectation, we found anisometropia to be rare at the age of 14 months: Of the 5 / 601 anisometropes at 14 months, 3 even became isometropic in the year after. In clinical practice, at age 6 half of the children with amblyopia have anisometropia. The very few children with anisometropia we find at 14 months strengthens the 1995 suggestion by Lynne Kiorpes and Josh Wallman that amblyopia might cause anisometropia (doi: 10.1016/0042- 6989(94)00239-i): Ten of the 19 monkeys they had operated into squint developed amblyopia after 10 weeks but developed anisometropia after 30 weeks, the latter in proportion to the difference in visual acuity. How then could amblyopia cause ansiometropia?

Two recent insights point to lack of accommodation of the amblyopic eye as a possible culprit.
First, it is now agreed among myopia researchers that emmetropisation – regulation of eye growth to reach emmetropia (no refractive error) – is a local eye process with defocus of the image in the retina enhancing or inhibiting the production of growth factors in the retina that migrate to the sclera that then grows or stops growing.
Secondly, accommodation (focusing) in the amblyopic eye was found to be less than that in the healthy eye in early laboratory studies (doi: 10.1097/00006324-197504000-00001, doi: 10.1007/BF00155676). This was denied in subsequent studies but has recently been reconfirmed in studies by orthoptists of their amblyopic patients, now possible because devices for bilateral real-time measurement of accommodation have become widely available.

We suggest that defocus of the image in the retina of the amblyopic eye by insufficient accommodation impedes emmetropisation of that eye and thereby promotes anisometropia. The questions remain how, in healthy individuals, the pathways from the two centers for accommodation in the oculomotor nuclei to the two ciliary muscles in the eyes are calibrated using binocular vision, whether the flocculus is involved in that process and how this calibration is frustrated by amblyopia.

Bio: Before retirement Huib Simonsz was paediatric ophthalmologist in the Sophia Children’s Hospital for 30 years but, before that, postdoc in the Netherlands Ophthalmic Research Institute with Alexander von Humboldt and K.N.A.W. fellowships. Current topics of the research group are screening for and treatment of amblyopia, strabismus and nystagmus, with emphasis on effectiveness and cost-effectiveness of vision screening, for example in the EUSCREEN Study in the Horizon 2020 program that compared vision and hearing screening in all 40 countries in Europe between 2017 and 2021 and the Early Glasses Study starting in 2021. He founded the journal Strabismus in 1992 and recently retired as its editor-in-chief.