This could be due to a variety of reasons. Decreased visual acuity might cause this. Glaucoma (raised intra ocular pressure) may cause this.
This could also be a tension headache or a migraine among other things.
The latter are most likely causes in most people.
Next Steps
Please get Vision tested and consult for further steps
Health Tips
Just googling/doodling and overthinking about it without actually getting tests, diagnosis and treatment can make headaches worse due to stress and anxiety. Start taking next steps and get on the path to recovery and a better quality of life