Published in Research

Anatomical brain changes noted in patients with restored vision

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4 min read

A new study published in the Proceedings of the National Academy of Sciences (PNAS) suggests that neuroplasticity in certain white matter pathways may be induced by vision restoration surgery despite the age of the patient.

Tell me about the research.

In a longitudinal study, researchers followed 19 cataract patients (13 male, 6 female) from Uttar Pradesh, India, between the ages of 7 to 16 years to track visual acuity (VA) performance over time.

The mean age at time of surgery was 12.34 years (±3.69). All patients had dense bilateral cataracts prior to 1 year of age and received IOL implants with additional refractive correction.

What was assessed?

Over the course of the study, patients’ VA was measured an average of 7.9 ± 3.9 times.

In the VA test, patients were asked to identify various stimuli at 40 cm. They also performed facial discrimination tests an average of 4.2 ± 2.0 times, in which they were asked to identify faces and “nonface objects.”

MRI scans were also performed on each patient.

Findings?

Patients experienced the most improvement in performance in the days immediately following surgery, and patients who received surgery at a younger age experienced greater improvement than those who received surgery later.

And … ?

However, the study authors noted, “while there is no evidence that time of surgery affects the [VA] improvement for these patients, face discrimination depends on a closing window of neural plasticity whereby surgery at a later age reduces the behavioral improvement.”

What’s that about brain plasticity?

Neuroplasticity can be defined as the ability of the brain to form synaptic connections, which is usually considered in the context of learning or injury recovery. The brain can develop at different rates, and the 10 major pathways that determine visual processing were divided by the study authors into early-visual, late-visual, and non-visual pathways.

Why “early-visual” pathways?

Early-visual pathways are called such because they develop earlier and are subject to a so-called sensitive period for development.

The study authors hypothesized that because of this sensitive period, the window for pathway development would have closed despite the later onset of visual input.

What else did they find?

Using MRI scans and 80 age-matched controls, the researchers analyzed the difference between age-related maturation effects on white matter pathways compared to the changes in those pathways following visual recovery.

While VA improved following surgery, researchers found no evidence that these improvements were linked to changes in any particular white matter pathways.

What about facial recognition?

Patients who received surgery earlier in life were more likely to experience greater improvement in face recognition; these improvements were also linked to specific changes in white matter pathways following surgery.

Which pathways?

Specifically, the structural changes occurred in late-visual pathways: the inferior fronto-occipital fasciculus (IFOF), the superior longitudinal fasciculus (SLF), the inferior longitudinal fasciculus (ILF), and the posterior forceps (also referred to as forceps major) of the corpus callosum.

So what does that mean?

Sight restoration, even in later adolescence, can kickstart the neuroplasticity of visual pathways.

While not all white matter pathways are affected, the “sensitive period” for vision development should not be considered a major barrier to treatment for patients who have “aged out” of it since the restoration of the visual pathway can still result in substantial neural and behavioral gains.