Snellen Charts

[Drew Radcliffe]

Hi All

I was wondering what our perception of the eye charts that we are all used to reading is.

I an constantly aware of my acuity is dependant on ambient light where the sun is or lighting source and other influences like movement.

So if I took the test in different locations at different times of the day my acuity would be different between location.

With this in mind is the test objective enough for our needs? Or am I an Odball Cyclopse.

D

[GarethB]

Drew,

I have found I see the chart better if the light box is off and the room I am in is near normal lighting.

This has been done every time I go to the hospital, so at least the conditions I see the chart are at least constant. This is the way my optom and I try and make things as objective as possible. In daily life I use a range of sunglasses to maintain as near constant light level as I can.

[Andrew MacLean]

Like gareth I wander about in various degrees of shades. Unlike him I like the snellen chart illuminated. My optician's examination room (I'm actually not sure if this is right) is in the basement, therefore no sun!

This all makes for a very varied approach. Still optometrists study to get degrees in dealing with patients with ideosyncratic requirements.

Andrew

[wheelnut]

I'm the same as you Andrew - I see it much better when it's illuminated and the lighting in the room is subdued.

In general I tend to see better when there is one source of light, otherwise, as someone else once described it, the light seems to get in the way.

[Lynn White]

The Snellen chart is generally designed to be used by people with "normal" vision. This usually means an illuminated chart in an evenly lit environment without any reflected glare.

However, with various eye conditions like cataracts and KC, glare becomes an issue. So if you get reflected light back from an illuminated chart, it gets bounced round your eye by the internal aberrations and distortions. This is why KC patients often see better with unilluminated charts.

Lynn

[Sweet]

I need to see it with the light on and it doesn't really matter what lighting the room has. I have tried it without the light box on and lost a whole three lines! I guess we are all different and just need to read it with the right lighting for us. Unique toads we are!

Sweet X x X

[John Smith]

Who are you calling a toad?

Ribbit.

[Andrew MacLean]

Now that reminds me of the Jake Thackery song. Those who remember him will smile knowingly, and those who do not cannot accuse me of having corrupted them!

I've been thinking about this whole snellen chart thing. I am used to using three configurations.

1 unlit (apart from ambiant light) chart on a wall a distance away.

2 unlit (apart from ambiant light) chart on a wall behind me and reflected in a mirror

3 chart mounted on a light box behind me and reflected from a mirror. This chart is usually read in an otherwise dark room.

My favourites are 1 and 3, but for different reasons. I used to tend to try to memorize the letters on type 2 before I sat down. this way I thought I'd be able to please the optometrist.

Actually, while I was at school, I got quite good at this. I'd glance at the chart and make up a little story: A Deaf Friend Had Zipped Pullovers, Timber Xylophones Under Duvets, Zebras And Double Neapolitan Handcream, Personalized Napkins That Upstaged His Xenophobes ...

You get the point.

I think it was in order to overcome this tendency in schoolboys to try to please visiting optometrists that they moved onto the light box option where they optometrist only scrolls round to the chart of choice once the patient is well and truly looking the other way!

Andrew

[Louise Pembroke]

Andrew please take your medication!

[Andrew MacLean]

Don't have any, Louise.

I did, however, ask my optometrist if I was right about the reason for the intrudiction of the 'light box'. She said I was

There are others like me out there. the worrying thing is that they are probably driving cars!

Andrew