Health boards in the north and north-east are missing waiting time targets for treating eye conditions.
The government has set a 12 week (84 day) target for ophthalmology treatment for inpatients and day cases.
But new statistics from the Royal Blind charity show that as of March, six Scottish boards are not meeting the guarantee – with four of them in the north or north-east.
NHS Orkney has the longest waiting times at 156 days, then Grampian at 143, Highland at 118 and NHS Shetland at a 91 day average.
The other two boards are Tayside, with 116 days, and the Borders with 92.
All the health boards are meeting targets for outpatient appointments.
Mark O’Donnell, chief executive of Royal Blind and Scottish War Blinded said: “It is vital that health boards and the Scottish Government now act to ensure all health boards meet waiting time guarantees for ophthalmology patients.
“Earlier this year the Royal College of Ophthalmologists produced its workforce census which actually showed there had been a decrease in the number of consultant ophthalmologists in Scotland at a time of rising demands.
“Action is required to show the specialist staff and resources are in place to ensure all patients with sight loss conditions get the treatment they need, when they need it.”
Aberdeenshire West MSP Alexander Burnett said: “The disparity between different parts of the country highlights the ongoing staffing issues for health boards in the north-east and Highlands.
“The health board is doing all it can to fill these specialist roles, but without action from SNP ministers, patients will continue to face long waits for treatment.”
An NHS Grampian spokesman said the board was “working hard” to resolve the issue and that urgent cases were prioritised.
Kathleen Carolan, director of nursing and acute services for NHS Shetland, said there had been challenges recruiting specialist staff.
She added: “As of mid June 2019, five patients are on our waiting list for surgery who have been waiting longer than 12 weeks for an inpatient or day case treatment, which is a much proved position over the last six months.”
An NHS Highland spokeswoman apologised for delays and said additional funding from the Scottish Government had allowed for operating on cataracts at weekends.
NHS Orkney chief executive Gerry O’Brien said: “Ophthalmology continues to present difficulties in terms of treatment times, the board is aware of the issues and we continue to introduce service improvements to assist the position.”
A Scottish Government spokeswoman said: “The health secretary has been clear that long waits are not acceptable.
“That’s why we’ve taken action to address this through our £850million waiting times improvement plan, which includes an investment of more than £200million in a network of new elective centres which will increase ophthalmic capacity.
“Through the plan we aim to substantially and sustainably improve waiting times so that no one is waiting longer than the waiting times standards and guarantees by spring 2021.”