- Medically Reviewed by: Mr Mfazo Hove, Consultant Ophthalmic Surgeon
- Author: Mr Mfazo Hove
- Published: December 17, 2024
- Last Updated: November 10, 2026
TL;DR: Cystoid macular oedema (CMO) is swelling of the macula, the central part of the retina responsible for detailed vision, where fluid collects in small, cyst-like spaces. It can cause blurred or distorted central vision after cataract surgery or alongside conditions such as diabetes, blocked retinal veins or inflammation inside the eye. Treatment depends on the cause, and many cases after cataract surgery improve over weeks to months.
CMO describes a pattern of swelling rather than a single disease. Treating it means identifying what is causing the fluid to collect.
What Happens in the Eye
The retina is the light-sensitive layer at the back of the eye. Its central area, the macula, allows you to read, recognise faces and see fine detail.
When small blood vessels around the macula become leaky, fluid can gather in cyst-like spaces between the retinal layers. The macula thickens, and central vision may become blurred or distorted.
Causes of Cystoid Macular Oedema
- After cataract surgery. Known as Irvine-Gass syndrome, this form of CMO develops because of inflammation following the operation.
- Diabetes. Damage to retinal blood vessels can cause diabetic macular oedema, which may have a cyst-like appearance on scans.
- Retinal vein occlusion. A blockage in a vein carrying blood away from the retina can cause blood and fluid to leak into the macula.
- Uveitis. Inflammation inside the eye can lead to macular swelling.
- Less common causes. These include some medicines and inherited retinal conditions such as retinitis pigmentosa, a group of conditions that gradually damage the retina’s light-sensitive cells.
CMO After Cataract Surgery
A UK study of 81,984 eyes found that 1.17%, approximately 1 in 100, developed postoperative macular oedema within three months when there were no operative complications, diabetes or other identified risk factors. This describes the study population, not an individual patient’s risk or Blue Fin Vision® outcomes.¹
Risk was higher in people with diabetes, previous uveitis, a membrane on the macula or a previous retinal vein occlusion.¹ Symptoms often appear a few weeks after surgery, when vision that had initially improved becomes blurred again.
In people without diabetes, the European PREMED trial found that combining steroid and non-steroidal anti-inflammatory eye drops reduced clinically significant macular oedema compared with steroid drops alone.² Your surgeon will prescribe preventive treatment according to your individual risk.
How Cystoid Macular Oedema Is Diagnosed
Optical coherence tomography (OCT) is a scan that uses light to produce detailed cross-sectional images of the retina. It shows the fluid-filled spaces and measures the thickness of the macula.
Your consultant assesses the scan alongside your symptoms, vision and examination findings to identify the cause. Repeat scans help monitor the response to treatment. Our article on OCT Scans explains the test.
CMO Treatment
Treatment is selected according to the cause of the swelling:
- Postoperative inflammation. Steroid and non-steroidal anti-inflammatory eye drops are commonly used for CMO after cataract surgery.³
- Persistent inflammatory swelling. Steroid injections around or inside the eye, or a slow-release steroid implant, may be considered if drops are insufficient.
- Diabetes or retinal vein occlusion. Anti-vascular endothelial growth factor (anti-VEGF) injections may be recommended. These medicines block a signal involved in blood vessel leakage.
- Uveitis or another underlying condition. Managing the cause is an important part of controlling the swelling.
- Mechanical pulling on the macula. Surgery is occasionally considered if a membrane or the gel inside the eye is pulling on the retina.
These are different treatment pathways, not steps that every patient must follow.
CMO Symptoms
CMO can cause:
- Blurred or misty central vision, particularly when reading.
- Straight lines looking bent or wavy.
- Colours appearing less vivid.
- Vision becoming blurred again after initially improving following cataract surgery.
CMO itself is usually painless and mainly affects central rather than side vision. However, the condition causing it may produce other symptoms, including pain or redness.
When to Seek Help
Contact your surgical team promptly if your vision worsens after initially improving following cataract surgery. Do not assume that the cause is CMO or wait for your next routine appointment.
Sudden sight loss, severe eye pain or increasing redness with worsening vision needs urgent assessment. Contact your surgical team or an urgent eye service immediately. If you cannot reach them promptly, attend your nearest eye casualty or A&E department. Do not drive yourself.
Who Is at Higher Risk After Cataract Surgery?
The UK study of 81,984 eyes identified higher risk in people with:¹
- Diabetes, even without diabetic retinopathy, and a greater risk when diabetic retinal damage was already present.
- Previous uveitis.
- An epiretinal membrane, a thin layer of scar tissue on the surface of the macula.
- A previous retinal vein occlusion.
- Complications during surgery, such as a tear in the lens capsule, the thin membrane surrounding the natural lens.
Assessing these factors before surgery helps your consultant plan preventive treatment and follow-up. NICE recommends considering combined steroid and non-steroidal anti-inflammatory drops for people at increased risk, including those with diabetes or uveitis.³
Do not extend or change prescribed drops without advice from your eye care team.
How Long Does CMO Last?
Many cases of CMO after cataract surgery improve over weeks to months with treatment. Some persist for longer and require additional treatment or monitoring. In most patients, postoperative swelling settles without a lasting effect on vision, although recovery is not guaranteed.⁴
The outlook depends on the cause, how long the swelling has been present and whether there is other retinal damage. CMO associated with diabetes, vein occlusion or uveitis may recur, so longer-term care may be needed.
Treatment According to the Cause
CMO After Cataract Surgery
Treatment commonly starts with anti-inflammatory drops prescribed for a period of weeks. Your consultant reviews your vision and repeats OCT scans to assess whether the swelling is improving.³
If swelling persists, a steroid injection or implant may be considered. The choice depends on your response to drops and the risks and benefits for your eye.
CMO Related to Diabetes or Vein Occlusion
Your consultant assesses the underlying retinal condition and whether injections or another treatment are appropriate. Anti-VEGF treatment does not necessarily follow a trial of postoperative drops: the treatment pathway is different.
CMO Related to Inflammation or Traction
Uveitis requires treatment of the inflammation inside the eye.
Vitreous traction means that the gel inside the eye is pulling on the retina. If traction or an epiretinal membrane contributes to persistent swelling, surgery may be considered in selected cases.
Steroid treatment can raise eye pressure in some people, so pressure is checked during treatment.
Can It Be Prevented?
CMO cannot always be prevented, but anti-inflammatory drops can reduce the risk after cataract surgery.
The PREMED trial found that combining steroid and non-steroidal drops reduced postoperative macular oedema compared with steroid drops alone in people without diabetes.² NICE recommends postoperative steroid drops and/or non-steroidal anti-inflammatory drops, with combined treatment considered particularly for higher-risk patients.³
People with diabetes or other risk factors may need an individualised treatment and monitoring plan around surgery. Good diabetes management remains important.
Frequently Asked Questions
Does CMO mean my operation went wrong?
No. CMO can follow entirely uncomplicated cataract surgery. It is an inflammatory response affecting the macula and is often temporary. Your consultant will assess whether there are any additional factors contributing to the swelling.
Will my vision recover fully?
Many people recover good vision as postoperative swelling settles, but full recovery cannot be promised. The outcome depends on the cause, duration of swelling and any other retinal damage. Persistent swelling may leave a lasting effect, which is why assessment and follow-up matter.⁴
Can it affect my other eye when I have that operated on?
Yes. Having CMO after surgery in one eye increases the risk after surgery in the other. Tell your consultant about the previous episode so they can plan preventive treatment and follow-up for your second operation.⁵
Is CMO the same as macular degeneration?
No. CMO is a pattern of swelling in the macula that can have several causes.
Age-related macular degeneration (AMD) is a separate condition affecting the macula as people get older. Wet AMD can also cause fluid to collect, but the diagnosis and treatment plan are different.
At Blue Fin Vision®
At our eye clinic, we use OCT and a full examination to identify what is causing cystoid macular oedema and recommend treatment accordingly.
Where CMO is driven by diabetes or vein occlusion and injections are needed, they are given at our Harley Street clinic the same day or the following day, followed by an organised next step with us or through the NHS.
Before cataract surgery, we assess your risk of CMO so prevention can be planned.
For more information about assessment and treatment:
- Our article on Macular Degeneration explains how our injection service works.
- Explore our Medical Retina service.
- Our Patient Information explains more.
Find out what is causing your macular swelling and what can be done to treat it. Book a consultation with Blue Fin Vision® for a consultant-led assessment and a personalised treatment plan. Our team cares for patients across London, Hertfordshire & Essex.
References
- Chu CJ, Johnston RL, Buscombe C, Sallam AB, Mohamed Q, Yang YC; United Kingdom Pseudophakic Macular Edema Study Group. Risk factors and incidence of macular edema after cataract surgery: a database study of 81984 eyes. Ophthalmology. 2016;123(2):316-23.
- Wielders LHP, Schouten JSAG, Winkens B, van den Biggelaar FJHM, Veldhuizen CA, Findl O, et al. European multicenter trial of the prevention of cystoid macular edema after cataract surgery in nondiabetics: ESCRS PREMED study report 1. J Cataract Refract Surg. 2018;44(4):429-39.
- National Institute for Health and Care Excellence. Cataracts in adults: management. NICE guideline NG77. London: NICE; 2017.
- Hull University Teaching Hospitals NHS Trust. Risks and benefits of cataract surgery [Internet]. 2018 Aug 1 [cited 2026 Nov 8].
- Shakarchi AF, Soliman MK, Yang YC, Sallam AB. Risk of pseudophakic cystoid macular edema in fellow-eye cataract surgeries: a multicenter database study. Ophthalmology. 2023;130(6):640-5.
ABOUT THE AUTHOR
Mr Mfazo Hove
MBChB MD FRCOphth CertLRS
Consultant Ophthalmic Surgeon | Founder and Medical Director, Blue Fin Vision®
Mr Mfazo Hove is a Consultant Ophthalmic Surgeon with more than two decades of experience across NHS and private practice and more than 57,000 ophthalmic procedures performed. He trained for six and a half years at Moorfields Eye Hospital and served for five years as an NHS consultant at the Western Eye Hospital, Imperial College Healthcare NHS Trust.
He specialises in cataract surgery, refractive lens replacement, laser vision correction and implantable Collamer lenses (ICL). He is the founder and Medical Director of Blue Fin Vision®, a private ophthalmology group providing consultant-delivered care across London, Hertfordshire and Essex. His cataract surgery outcomes are publicly reported through the National Ophthalmology Database.
A ZEISS Key Opinion Leader and international speaker, Mr Hove is a contributing author to The Ophthalmologist and Ophthalmology Times. His writing examines how clinical governance and the organisation of ophthalmic services shape patients’ experiences and outcomes, with a focus on transparent outcome reporting, surgical training and long-term accountability for patient care.
