Hi Tim Bridgett,
Eye tests are considered exempt if they are required by health and safety legislation for employees who use a computer monitor or other screen.
Expenses and benefits: medical or dental treatment and insurance
If the eye tests do not meet the exemption criteria, then a benefit will arise.
As to how to report this, depends on how the benefit has been arranged and paid for.
Where reimbursement has been made to an employee, the payment is treated as earnings and reported via the payroll for tax and Class 1 NIC.
Expenses and benefits: medical or dental treatment and insurance What to report and pay
I hope this clarifies, however, should you need any further assistance, please contact the Employer Helpline on 0300 200 3200.