Hi and welcome to the forum
The eye isn't white so it's unlikely the fish is blind.
Fish kept in bad water will often appear blind and just slowly move around looking unwell. The poor water quality will also reduce their feeding instinct.
How long has the tank been set up for?
How long have you had the fish for?
Have you added anything to the tank in the 2 weeks before this started?
What are the tank dimensions (length x width x height)?
What is the ammonia, nitrite, nitrate and pH of the water?
What sort of filter is on the tank?
How often and how do you clean the filter
How often do you do water changes and how much do you change?
Do you gravel clean the substrate when you do a water change?
Do you dechlorinate the new water before adding it to the tank?
Are there any plants, ornaments or caves in the tank?
Can we get a picture of the entire tank to see how it's set out?
What do you feed the fish?
When do you feed them (what time of day)?
How does the fish react when you feed it?
Are there other fish in the tank that eat the food?