What causes an epiretinal membrane?

What is an epiretinal membrane?

An epiretinal membrane, or ERM, is a thin sheet of fibrous tissue on the inner surface of the macula. The macula is the small central part of the retina responsible for detailed vision, including reading and recognising faces. When the membrane tightens, it can wrinkle the tissue beneath it — hence the name “macular pucker”.

The membrane is at the back of the eye. It is different from a cataract, which is clouding of the lens nearer the front.

How can vitreous separation lead to a membrane?

As we get older, the vitreous gel becomes more liquid and its attachment to the retina weakens. It can then separate from the retinal surface: a posterior vitreous detachment, or PVD. This common ageing change is also a frequent cause of new floaters.

Separation is not always clean. The thin outer layer of vitreous can split, leaving microscopic remnants on the macula. These remnants contain cells called hyalocytes and can provide a surface on which cells multiply and lay down new fibrous material. Some acquire the ability to contract, pulling on the underlying retina.

Retinal support cells, known as glial cells, may also reach the surface and contribute. One proposed route is through tiny defects in the retina's surface layer during vitreous separation. The relative contribution of these pathways varies, and the exact sequence is not fully understood.

This is more than a piece of gel simply sticking to the retina: an ERM is living, cell-containing tissue that can grow and tighten over time.

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Does everyone with a PVD develop a membrane?

No. Most PVDs do not cause lasting visual problems. A membrane is a possible consequence of changes at the vitreous–retina junction, not an inevitable stage of ageing.

An ERM can also develop while the vitreous remains partly attached, or without a clinically recognised PVD. When no other eye disease or injury explains it, it is called a primary or idiopathic ERM. “Idiopathic” means that no specific underlying cause has been identified; it does not mean the diagnosis is uncertain.

What other conditions can cause a membrane?

A secondary ERM develops in association with another eye condition or event. Examples include:

• Retinal tears or detachment: cells can reach the retinal surface through a break, and repair processes can stimulate membrane formation.
• Retinal surgery or laser treatment: membranes sometimes develop after treatment, particularly treatment for tears or detachment. The underlying retinal problem and the eye's healing response may both contribute.
• Retinal vascular disease: diabetic retinopathy and retinal vein occlusion can be associated with ERM.
• Inflammation inside the eye: conditions such as uveitis can promote cell growth on the retinal surface.
• Eye injury: trauma may disturb the vitreous and retina and trigger scarring.

ERM can also be detected after cataract surgery. Finding one after an operation does not establish when it began or prove that the operation caused it; a subtle membrane may already have been present.

Why does a membrane make straight lines look wavy?

As an ERM contracts, it pulls across the macula and changes the arrangement of retinal tissue. Straight lines may look bent, letters may crowd together and fine detail may become harder to see. Some people notice very little change, even when a membrane is visible on a scan.

This distortion comes from the macula. Moving specks or cobwebs are usually floaters in the vitreous, although the two problems can occur together.

What should optometrists look for?

The clinical question is both “How much is this affecting vision?” and “Is there an underlying retinal problem?” A useful assessment includes:

• History: onset and progression of distortion, reading difficulty and binocular symptoms; previous tears, detachment, surgery, laser, uveitis or trauma.
• Function: best-corrected acuity in each eye, symptoms with each eye tested separately, and the effect on ordinary tasks. Good letter-chart acuity does not exclude troublesome distortion.
• Dilated examination: assess the macula and look for secondary disease, including peripheral retinal pathology where indicated.
• OCT: document the surface membrane, foveal contour and retinal layers, and any coexisting traction, fluid or macular disease. Compare with earlier scans.

For referral, include symptoms, their impact, acuity, relevant history and OCT images where available. Progressive distortion or increasing difficulty with daily activities warrants ophthalmic assessment; there is no single acuity or retinal-thickness threshold that suits every patient.

Does the cause change the treatment?

It helps explain what else needs attention. In a secondary ERM, inflammation or vascular disease may need treatment in its own right. Treating that condition does not necessarily remove an established membrane.

Mild, stable membranes can often be monitored. If vision is becoming troublesome, vitrectomy and membrane peeling may be considered. The decision weighs symptoms, progression, retinal health and surgical risks, as explained in epiretinal membrane: surgery or observation.

Improvement is usually gradual over months and may be incomplete. Risks include retinal tear or detachment, infection, and cataract progression in an eye that still has its natural lens. The separate article on why vitrectomy can cause cataracts explains that connection.

Watch Dr Chen remove an epiretinal membrane

3:33Epiretinal membrane surgery

This video shows real eye surgery: vitrectomy followed by peeling the membrane from the macula.

Watch on YouTube →

Where can I read more?

For a fuller clinical discussion, read Epiretinal membranes — Dr Simon Chen and Dr Chris Hodge, mivision, May 2020 (PDF). It covers assessment, monitoring and surgical management for optometrists.

When should I seek urgent help?

A known ERM should not be used to explain away a sudden change in vision. New flashes, a sudden increase in floaters, a dark curtain or shadow, or sudden loss of vision need urgent assessment. These can indicate a retinal tear or detachment or another problem requiring prompt treatment.

Contact your ophthalmologist urgently, or attend an emergency department. Gradually worsening central distortion also deserves review, even without these warning signs.