Reading the fine print: correcting ametropia in infant visual acuity studies

(extracts only)

The role of infant nutrition, in particular, long chain omega-3 polyunsaturated fatty acids (LCPUFA), in the function and development of the nervous system is a critical issue.

It is relatively well understood; the visual system has been the subject of many studies to investigate the effect of LCPUFA in neural development.

The effect of ametropia on VA is well known and forms the basis of clinical refraction in the profession of optometry. Infants have relatively high ametropia, with a mean of two dioptres of hypermetropia (+2.0 D), and standard deviation of about 2.75 D. In the absence of ocular pathology, ametropia accounts for the majority of variation in VA. Uncorrected ametropia, in particular astigmatism (found in 50 per cent of infants younger than one year), could easily account for inter-study disparities, particularly in small study groups that have not been matched for ametropia. In fact, the VEP has been proposed as an accurate tool for estimating ametropia. Therefore, when assessing VA, strict exclusion criteria for ametropia must be implemented.

As changes in the retina could account for most of the effects on VA attributed to LCPUFA, retinal assessment is obligatory before any conclusion regarding cortical development can be reached. Most of the VA studies did not perform flash electroretinography, a test independent of ametropia. Moreover, as the development of VA in infants largely reflects the development of the retinal fovea, one wonders whether VEP - or behaviourally - assessed acuities are appropriate indices of cortical function in infancy.

A great amount of time, effort and resources have generated conflicting results that, as a group, are difficult to interpret. Until these issues are addressed, the question of whether LCPUFA have demonstrable and reproducible effects on visual development will not be answered.

Clin Exp Optom 2003;86:1:65-66

Letter to the editor

Harrison S Weisinger MScOptom PhD
Section of Neurobiology, Howard Florey Institute of Experimental Physiology & Medicine, University of Melbourne; Laboratory of Membrane Biochemistry and Biophysics, National Institute on Alcohol Abuse and Alcoholism, USA
Drake C Mitchell MS PhD
Laboratory of Membrane Biochemistry and Biophysics, National Institute on Alcohol Abuse and Alcoholism, NIH USA
Konrad Pesudovs BScOptom PhD
Department of Ophthalmology, Flinders Medical Centre


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