Neuroplasticity at the Retinal Level


A new article in PLOS One provides some answers to questions that we posed in September 2012 about Structure vs. Function.  If a mismatch between the visual channels of the two eyes results in alterations visible at the micro-structural level, might foveal anatomy be altered through interventional therapy in a way that changes the relationship between the eyes anatomically?  If so, this would be yet another indication (as established by the PEDIG studies) that optical treatment in hyperopic anisometropia is a very powerful intervention.  The article, Effect of Optical Correction on Subfoveal Choroidal Thickness in Children with Anisohypermetropic Amblyopia, suggests that this is indeed the case.

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As background, the article cites literature that eyes of children with aniso-hypermetropic amblyopia have differences in the retinal microstructures and choroidal structures of the fovea from that of normal eyes. The choroid plays an important role in the modulation of the refractive state, and its development can be affected by uncompensated refractive problems.

Many clinical studies have shown that the best-corrected visual acuity (BCVA) is significantly improved in amblyopic eyes after wearing corrective lenses. Furthermore, an increase in the outer segment length of the fovea was detected in the amblyopic eyes after optical treatment.  However, it has not been determined whether wearing optical correction for aniso-hypermetropia will alter the CT in the eyes of children with amblyopia as measured by enhanced depth imaging of spectral domain optical coherence tomography (EDI-SD-OCT).  The purpose of this study was to determine if the wearing of appropriate lenses improved BCVA in conjunction with changes in choroidal thickness in aniso-hypermetropic amblyopia one year after the Rx was prescribed.

journal.pone.0189735.g002The yellow arrow indicates subchoroidal thickness (CT).  It’s measurement normally shows relatively similar CT between the two eyes, but differs between the eyes in the presence of unilateral amblyopia.  Interestingly and somewhat counter-intuitively, the study shows that subfoveal CT in eyes with thicker choroid tended to decrease and the eyes with thinner choroid tended to increase in both the amblyopic and fellow eyes.

Images E and F are findings in a 5-year old control child with normal acuity. At baseline, the subfoveal CT in the control eye (right eye) was 235 μm. One year later the thickness of the subfoveal choroid in the control eye was 222 μm, which was not significantly different from that at the baseline.

Images C and D are findings in a representative 9-year-old amblyopic patient whose CT was decreased after wearing the Rx.  At baseline, the subfoveal CT in the amblyopic eye was 391μm, and one year after wearing the Rx was  279 μm.  Initial BCVA was 0.5 logMAR units (20/63 Snellen) in the left amblyopic eye.  One year after wearing the optical correction, BCVA of the amblyopic eye improved to 0.2 logMAR units.

Images A and B are findings in a representative 4-year-old amblyopic patient whose CT was increased after wearing the Rx.  At baseline, the subfoveal CT in the amblyopic eye was 281 μm, and one year after wearing the Rx was 393 μm.  Initial BCVA was 0.5 logMAR units (20/63 Snellen) in the left amblyopic eye. One year after wearing the optical correction, BCVA of the amblyopic eye improved to 0 logMAR units (20/20 Snellen).

In other words, the study shows that wearing a spectacle Rx results in the two eyes undergoing a change in EDI-SD-OCT, such that eyes with a thicker choroid underwent choroidal thinning, and eyes with thinner choroid had choroidal thickening both in the amblyopic and the fellow eyes.  This provides evidence that the Rx induces changes in the subfoveal CT in aniso-hypermetropic amblyopic eyes to minimize differences in macular choroidal thickness between the eyes, thereby supporting improvement in BCVA.

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As is often the case, the answers provided here invite more questions.  Does the binocular status of the child prior to treatment influence these changes?  No data is provided regarding the presence of strabismus, or the sensory status in terms of fusion or stereopsis.

Spectacles for the amblyopic eyes and fellow eyes were prescribed at the first visit, and the power of the spectacles was the full correction determined by an auto refracto/keratometer after cycloplegia.  Given that some children reject full cycloplegic Rx correction, would alternate approaches to prescribing influence the OCT measurements?

All patients underwent one year of optical treatment, but patching therapy was added after 12 weeks in 15 of the 24 cases. The patching treatment consisted of an adhesive patch worn over the preferred eye for 2–3 hours/day.  Given the recent evidence that binocular integrative therapy can result in significant improvement in function without the need for patching, would such therapy influence the OCT measurements?

2 thoughts on “Neuroplasticity at the Retinal Level

  1. It is interesting that the researchers decided to investigate this possibility and more amazing how the systems responded. Thank you. Gary

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