How Asa sees

We got three new pieces of information this week – about Asa’s vision, the state of the tumours in his eyes, and the genetic basis of his condition.

1. How Asa sees

On Tuesday afternoon, an orthoptist tested Asa’s vision. She waved toys in front of him to assess how well he could track moving targets, and used a set of cards with images of varying clarity printed either on the left or right, or top or bottom, to see whether he could discriminate between image and blank space.

Taken together with what we know from other examinations, the results suggest that Asa’s vision is worse than we’d supposed based on his everyday behavior.

In the right eye he probably has good vision only on the periphery, and in the left eye his vision is probably blurry.

The reason is that the right eye has a centrally located tumour, and in the left eye – while the tumours are located lower down, affording a decent visual field – what he sees is probably blurred on account of retinal detachment.

Squint with your left eye and hold your fist about 6 inches in front of your right eye. That’s probably roughly what Asa can see.

But now imagine that this is all you’ve ever been able to see. That this is what the world has always looked like.

Then this way of seeing ceases to seem so poor.

By combining two deficient signals, and using them to the max, Asa seems to achieve something equivalent to what one good eye could do.

His ability to navigate – walking around, exploring – is good on account of the peripheral vision in his right eye, while his ability to manipulate things directly in front of him, make eye contact and so on, relies mainly on the central vision in his left eye.

He carries this off so well that we’d come to doubt that he was really visually impaired.

2. State of the tumours

The next morning Asa’s eyes were examined under general anaesthetic.

In the left eye, there was no change since last time. But two small tumours in the right eye have shown new growth over the past 6 weeks.

These were treated with cryotherapy – a freezing probe directed precisely at these spots. The cryo needs repeating to be effective, so Asa will be back for more in 3 weeks time.

3. Genetics

Results of the genetic test confirm that Asa has a change in the gene that regulates retina development. It's a strong change – a “fully penetrant mutation” – of the sort that almost always results in bilateral retinoblastoma.

This is what we expected.

The good news is that neighbouring genes are OK.  Asa’s not at risk of any other developmental abnormality.

Blood was also taken from Selam and me for testing, to check whether we have changes in our RB genes that could lead to a risk of retinoblastoma in other children we might have in future. These results will take a couple of months.

Round up

What we’ve learned will take a bit of digesting. But we have a much clearer understanding now of the state of Asa’s eyes. What comes with this is a heightened concern that he should retain what he has.

If there’s deterioration in either the peripheral vision in his right eye or the central vision in his left, he will likely end up much more compromised.

That said, some things we knew already bear repeating:

With the monitoring and treatment that Asa will receive over the coming years, this disease is very unlikely to endanger his life. The worst case scenario is blindness.

The period of the greatest danger in terms of tumour activity is from birth to 3 years. From 4-5 years, there’s a continued risk. After 5 years the risk decreases greatly.

Until that window closes, we won’t know what the long-term prognosis is, in terms of his sight. From month to month there may be changes, and it’s unpredictable. So we have to keep watching, and respond to problems as they arise.