There has to be a reason for reduced vision. If there is a squint or significant difference in glass power between the two eyes that may be a reason for amblyopia or weakness of the left eye since childhood.
Next Steps
Get a complete eye examination. if it's amblyopia unfortunately it may not be possible to improve at your age but if there is another treatable reason we should look for it.
Health Tips
For a teaching job it should not affect your ability to work but you should check with the institute if they have any eligibility criteria.