It could be for a couple of reasons, a small amount of astigmatism is normal, as is a small amount of hyperopia (long sightedness), maybe it doesn't make any difference to the amount of letters they can see on the chart.
We have a couple of methods of determining if a child can actually see, but isn't on the day - by switching the distance we are getting them to view the chart, or by using single line only testing. If things don't add up sometimes a wait and see method is a good idea when everything looks normal and healthy apart from a very small prescription and poor acuity levels.
I do usually write to the teacher as well, to let them know that they are maybe not seeing quite as well as they could be and that they need to be near the front of the class.
I mainly see children now and usually ones who are having eye problems and I've noticed that every two months or so, I get a child (and oddly it's often an 8/9 year old girl) who either isn't seeing very well (often with poor focussing as well) or is experiencing odd visual symptoms - seeing pink spots that sort of thing.
I often referred for an opthalmologist's opinion, but they couldn't find anything abnormal.
If things haven't sorted themselves out in a couple of months, (and 50% do) I often find some of the following help:
- Exercises to stimulate accommodation.
- Mindfulness/relaxation/yoga with less time on a phone/tablet.
Occasionally a low prescription does help as well.
HTH - happy to answer any questions.