How high is too high for blood sugar before cataract surgery?
We have always been taught, and have always taught, that blood sugars should be well controlled before a cataract operation . I have seen over a number of years patients whose surgery has been repeatedly delayed whilst their blood sugar is being managed and but who have gradually lost vision whilst waiting. A patient was referred to me this week whose cataract operation in the NHS had been cancelled several times. He presented with a dense cataract also quite obviously problems with diabetic macular oedema which needed to be addressed.
I want in the post to flag up that there are some people for whom we need to get move eye treatment forwards even if sugar control is not quite optimum.
Diabetic maculopathy in a patient with cataract.
What are we concerned about?
The two main additional risks are considered the risk of infection particularly intraocular infection which of course can be very serious and, secondly, the risk of exacerbated macular oedema after the operation.
Risk of macular oedema and accelerated retinopathy - yes
Patients who undergo uncomplicated cataract surgery have a risk of developing macular oedema after the operation of the order of 1 to 3% and is considered that patients with poorly controlled sugars have an increased incidence which can obviously impact negatively on vision after the surgery and would also pose a further problem in terms of further treatments being required.
One of the problems for individuals who have quite dense cataracts is that it becomes increasingly difficult to monitor, evaluate and treat any diabetic retinopathy and therefore the cataract surgery is required both for vision but also for medical management of the retina
I have seen a number of patients over the years whose cataract surgeries have been repeatedly deferred pending better control of blood sugar which is a process that can take a number of months and over that time I have seen diabetic retinopathy maculopathy getting worse and subsequently more difficult to treat.
A stable dry retina would be ideal prior to a cataract operation but this should not be the rate-limiting step. These days however any additional risks can be mitigated by giving an individual injection of anti-vegf at the time of the cataract operation ( or closely afterwards - within a month or so), monitoring closely post surgery and giving a prompt injection of anti-vegf if required . I've used this product approach of a number of years and not seen any patients who had accelerated retinopathy or maculopathy after surgery provided that the macula and retina are covered during the recovery period with intravitreal injectios such as Lucentis or Eylea or corticosteroid.
Ideally, of course, we would like the retina to be stable and blood sugar under good control prior to cataract operation. Note that
overly rapid control of blood sugar can conversely exacerbate and precipitate accelerated retinopathy .
The majority of patients I guess can have their blood sugar reasonably well controlled in preparation for surgery (within a period of perhaps three or four months) but I have seen,, repeatedly a small subsection of patients whose blood sugar of course is more resistant or there are personal social circumstances which makes it more difficult and these are the patients who surgeries get delayed and the blood sugars never really come under optimum control and the retinopathy keeps getting worse
In these circumstances I think it is better to go ahead with surgery when the sugar is under reasonable control rather than optimum control and then to evaluate and treat any retinal issues as soon as possible after the operation . This is a much better situation than letting the retinopathy go downhill prior to surgery and then being in a very difficult position to try and retrieve this after the cataract operation has been done.
Risk of endophthalmitis - some evidence says increased risk in diabetics - other evidence says not - no evidence at all related to level of control.
Let's address the first risk of which is infection . What is the really an increased risk of severe intraocular infection after a cataract operation (called endophthalmitis) if the blood sugar is high on the day of surgery ? The data about this is limited - particularly since we started quite a few years ago giving intraocular antibiotics during surgery.
The best available evidence from the UK suggests that without prophylaxis, the risk of endophthalmitis after cataract surgery is in the order of 0.14% (about 14 cases per 10,000 surgeries). However, when intracameral antibiotics—typically cefuroxime—are administered at the close of surgery, this risk declines significantly. While exact figures can vary by study and may depend on surgical factors and protocols, many reports (including those underpinning national guidelines) indicate that with prophylaxis the incidence is reduced to around 0.03% to 0.05%—roughly cutting the risk by more than half.
Increased risk of endophthalmitis in diabetics:
No significant increased risk of endophthalmitis in diabetics; no relationship to HbA1c:
This means that, even with a possible increased risk profile, tthe absolute risk remains very very small, indeed especially if precautions are taken to avoid intraocular complications during surgery ( eg by using experienced surgeons rather than trainees) and by giving intraocular antibiotics.
This needs to be weighed agains the risk of uncontrolled retinopathy occurring during a period of delay.
Are there any guidelines?
When we are, talking about the control of the time of the operation we are of course talking about optimum control, reasonable control and poor control . iI the control sugar is very poor on the day of surgery with very high blood sugars then of course there are other issues that we need to be concerned about particularly in terms of systemic complications immediately following the surgery. We will not want to send somebody home after cataract operation for them to go on and develop other problems
Yes, there are guidelines and recommendations in the UK, EU, and USA regarding blood sugar management in diabetic patients undergoing cataract surgery, though they vary slightly and are often based on broader perioperative diabetes management principles.
United Kingdom
The Royal College of Ophthalmologists (RCOphth) and associated bodies (e.g., Joint British Diabetes Societies, Association of Anaesthetists) provide the following guidance:
No strict HbA1c cutoff is mandated for cataract surgery under local anaesthesia.
An HbA1c above 69 mmol/mol (8.5%) has been used anecdotally as a threshold for postponing surgery, but this is not universally enforced[1].
The decision to proceed should consider:
The patient's functional vision needs.
The ability to manage diabetes postoperatively.
The clinical judgment of the surgeon and anaesthetist.
There is no specific level of control recommended for the day of surgery
[1] Diabetic control and safe cataract surgery - The Royal College of ...
European Union (EU)
While there is no single EU-wide guideline specific to cataract surgery, most countries follow European Society of Anaesthesiology and national diabetes society recommendations, which align with UK and US practices:
Aim for stable glycaemic control preoperatively.
Avoid surgery if the patient is acutely unwell or has poorly controlled diabetes (e.g., symptomatic hyperglycaemia or ketosis).
United States (USA)
Institutions like the Cleveland Clinic and American Diabetes Association (ADA) recommend:
Pre-meal blood glucose target: 90–130 mg/dL (5.0–7.2 mmol/L).
Bedtime glucose target: 100–140 mg/dL (5.6–7.8 mmol/L) [2].
Surgery should ideally be scheduled early in the day to minimise fasting-related glucose fluctuations.
Patients should bring a record of recent glucose readings and follow individualised medication adjustments.
References
[2] DIABETES GUIDELINES BEFORE SURGERY - Cleveland Clinic
Summary
In an ideal world, blood sugar should be optimally controlled before cataract surgery but should not unduly delay the cataract operation for visual rehabilitation and medical treatment of the retina.