Many parts of the NHS are "failing" to provide life-changing cataract surgery for patients, a charity has warned.
There is a postcode lottery of care across England, with patients in some regions being able to access the surgery promptly while people in other regions are forced to wait for months before they are treated, according to a new report from the Royal National Institute of Blind People (RNIB).
Some parts of the NHS are reducing the number of operations they perform, despite rising demand, the charity found.
Meanwhile, patients in some regions are being forced to wait up to 15 months for their operation.
People in Enfield in London are waiting on average 467 days between their first attendance at a hospital outpatient clinic to the subsequent cataract surgery.
Patients in Luton wait for just 15 days on average, the report states.
There is "noticeable variation" in the rates of cataract surgery taking place across England - out of every 100,000 people living around Scarborough and Ryedale, 1,166 procedures are carried out.
But in Tower Hamlets in London there are just 328 procedures per 100,000 people, the authors added.
"There is inequitable access to cataract operations across England," the report states.
"In many areas of the country the NHS is failing to provide access to cataract surgery when patients desperately need it.
"When a cataract begins to affect a person's quality of life, their sight will only continue to deteriorate.
"They will require surgery at some point in the future and not treating now will only increase waiting lists in the future."
Denying patients treatment leaves them at risk of depression, social isolation and fall-related hip fractures, the charity warned.
Cataracts occur when changes in the lens of the eye cause it to become less transparent, which results in cloudy or misty vision.
This can prevent someone from driving, undertaking work that requires fine detail and recognising faces.
Surgery to remove and replace the affected lens is the most common surgical procedure carried out in the NHS, with almost 400,000 cataract operations performed in 2015/16.
RNIB's group director of engagement Fazilet Hadi said: "Health Secretary Jeremy Hunt said access to cataract treatment should be based on clinical need first and foremost.
"RNIB agrees but our latest research proves that this is not what is happening.
"The postcode lottery of services means patients with cataracts are regularly being denied access to timely treatment on the basis of where they live.
"When a cataract begins to affect a person's sight, their vision only gets worse. The impact of delaying cataract surgery puts people at risk of injury through falls, makes doing everyday things difficult or impossible, and can lead to feelings of isolation. These consequences can lead to health and social care expenditure, which is more than the cost of cataract treatment.
"We urge Mr Hunt to tell commissioning groups to immediately implement the cataract commissioning guidance so patients are given the best care when they need it most.
"He has the power to change the lives of thousands of older people with cataracts."
David Geddes, national head of primary care commissioning at NHS England, said: "Over the last decade there has been considerable investment to improve access to cataract surgery.
"Most patients are now treated within 18 weeks, whereas in the 1990s patients were waiting a year or more for cataract surgery, by 2010 approximately 90% of patients were seen within 18 weeks.
"Cataract surgery is the most commonly performed elective surgical procedure in the NHS, with around 390,000 cataract operations performed per year in England and the need for surgery is likely to rise as the NHS cares for an ageing population.
"To reduce pressure on hospital eye services, pre and post-cataract care is increasingly being provided through community optometry services."