Jul 202012
 

Earlier this month Dad and I travelled to Leicester for eye appointments for Jack and Isaac spread over two days.  The primary purpose was to take part in the OCT hand held scanner trial, but it was also to;

– Carry out VEP (visual evoked potential) and ERG (electro-retinogram) tests
– Carry out a visual acuity test to check whether Jack needs glasses
– Check whether Jack has Ocular Albinism
– Find out more about  the chances of us/our children passing on nystagmus genes
– Check whether Isaac has nystagmus

OCT hand held scanner trial tests
Since our last appointment, the Doctors have carried out over a hundred tests with their new scanner and learned good techniques to help take the images of the eye they need.  Playing a children’s DVD and providing a personal puppet show worked very well on Jack, and they got the data they needed within minutes.  Isaac provided more of a challenge!  He kept turning his head away from the scanner or shutting his eyes at the crucial moment.  We tried him in a number of positions and scenarios on two different days including in the car seat and out, and different positions on Mum and Dad.  The Doctors were very patient.  We asked whether they would like to use some clips to help keep his eyes open (as I’d seen used when Jack was first diagnosed but they said they would prefer to get him to co-operate naturally so as not to put him off for future visits.  This is important as we are required to attend appointments every three months up to age 2, and every six months until age 5.  We got there in the end!

VEP/ERG tests
The VEP and ERG tests were very similar to the ones Jack had at the RVI (Royal Victoria Infirmary) at Newcastle in May 2011, although the machine was rectangular shaped instead of eyeball shaped.  Unfortunately neither Jack nor Isaac were as co-operative as Jack was the first time.  Both cried throughout most of the tests despite the excellent staff trying to put them at ease.   It was reassuring to learn it’s usually only necessary to carry these out once so they shouldn’t have to have them again.  The results from the tests will take at least a week to process and the Doctor will explain the results in person at our next appointment in approximately three month’s time.

Visual Acuity tests
Both Jack and Isaac were tested for their visual acuity (how good their vision is) to see whether they need glasses.  For adults this is usually done with a Snellen chart but for young children it’s often done with Teller acuity cards (which take advantage of their natural preference to look at patterns rather than plain surfaces).  Both Jack and Isaac were tested with rectangular cards similar to those in the picture below (but with patterns at each side within circles).

                    

Visual acuity is measured as a fraction.  A visual acuity of 20/20 is the standard measure for normal eyesight.  It means a person can see detail from 20 feet the same as a person with normal eyesight can see it from 20 feet.  If a person has 20/40 eyesight they can see detail from 20 feet the same as a person with normal eyesight can see it from 40 feet.  If acuity is greater than 20/200 (with correction e.g. glasses) a person is classed as legally blind.  If it’s less than 20/20 (e.g. 20/10) a person has better than average eyesight.  Here’s a conversion chart showing the relationship between the Snellen and Metric versions (the Doctors at Leciester use the metric version).

Feet (Snellen)   Meters (Metric)
20/10 =                 6/3
20/20 =                 6/6
20/50 =                 6/15
20/80 =                 6/24
20/100 =               6/30
20/200 =               6/60
20/300 =               6/90

Jack’s visual acuity was 20/100 (6/30).  The average for a healthy child his age without nystagmus is 20/80 (6/24) so he is below average.  However, the Doctor confirmed he doesn’t need glasses yet which is good news.  Isaac’s vision was 20/300 (6/90) which is as it should be for his age.

Ocular Albanism?
There are a couple of clues pointing towards a diagnosis of ocular albanism for Jack;

1)     The OCT scanner images showed he has forveal hypoplasia (an underdeveloped forvea – which is the small depression in the retina of the eye where visual acuity is highest) in both eyes.  Isaac’s are as expected for his age so far.
2)     I have iris TIDs (trans-illumination defects) which are common in female carriers of albinism.  They are small holes in the eye that let too much light through and can cause photophobia (light sensitivity).  Dad was checked this visit and showed no evidence of being a carrier.

To confirm the diagnosis the Doctor needs to analyse the electro diagnostic test (VEP and ERG) results and collect and review genetic samples.

Genetic testing
The Doctor gave us a kit to collect a saliva sample from Jack to check for the type of albinism and chances of us and our children passing on the genes.  The kit included a plastic tube to spit into but despite our best efforts we weren’t able to collect enough whilst we were there.  The Doctor is going to send us a new kit by post with a pipette for us to try again and send back to them.

Does Isaac have nystagmus?
Unfortunately there is not enough evidence to say one way of the other yet.  The Doctor said his forvea is developing well so far and if he does have it it should be milder than Jack’s which is good news.  Jack’s nystagmus presented between three and four months and Isaac is almost at the same age.  We’ll know for sure soon.

 

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