You asked

What should I do if my child gets something poisonous in his eye?

If your child gets any kind of a chemical in his eye, like a household cleaning product or a pesticide for instance then treat it as an emergency.
Quickly take him to the sink and pour warm (never hot) water into his eye for a full fifteen minutes. If there is another adult present they can hold the eye open while you pour the water in using a clean glass. This may be difficult but it’s extremely important to cleanse the chemicals from his eye to prevent permanent vision loss.
Then bring your child and the container of the chemical to the hospital (A&E) as soon as possible.
You should always keep any chemicals or anything harmful to your children well out of their reach.

More questions

Children's eyes are sensitive so it is vital to protect them from the sun's harmful rays.
Your young child can have their eyes tested even if they can't read
Regular eye exams are essential in order to monitor your child's eyesight.
There are some signs to watch out for if you think your child may have a vision problem. 
Should your child get any kind of chemical in her eye you should treat it as an emergency and bring her to the hospital immediately.
You should take your child to their G.P. or to the hospital if you notice any of these symptoms. 
You should seek immediate medical attention if an object seems to be imbedded in your child's eye. 
If your child appears to have something in his eye you should seek immediate medical attention if it is imbedded in the eye. 
As your baby learns to crawl and begins to explore her surroundings you will need to child proof your house to prevent eye injuries.
Babies and young children are always getting up to all sorts of mischief and eye injuries are quite common. It is important to always consult with your G.P. should any eye injuries occur.