The macula is the part of the retina responsible for sharp vision due to its high density of cone photoreceptors. It is situated at the back of the retina (the posterior pole), lying about 3 mm lateral to the optic disc. It has a central depression known as the fovea centralis. There are nothing but tightly packed cone photoreceptors in the fovea with no overlying blood vessels. This is where visual acuity is ultimately determined.
Macular oedema refers to the accumulation of fluid within the retina at the macular area (distinct from the condition where the fluid accumulates under the retina). The pathophysiology depends on the primary cause but usually, the end-point is vascular instability and a breakdown of the blood-retinal barrier.
This is frequently - but not always - cystoid in nature (cystoid macular oedema (CMO)) which is characterised by intraretinal oedema contained in honeycomb-like spaces. CMO is a common pathological response to a variety of insults:
- Following intraocular surgery: where CMO occurs as a consequence of surgery (between one and 12 months postoperatively, peak: six to ten weeks postoperatively) it is known as the Irvine-Gass syndrome. It is thought to occur as a result of release of inflammatory mediators within the eye and, if it is prolonged or recurring, permanent damage can occur.
- In central (and occasionally) branch retinal vein occlusions: venous occlusion causes a rise in intravenous and capillary pressure, leading to stagnation of blood, hypoxia of the affected structures and damage to the capillary endothelial cells, so ending in extravasation of plasma constituents. In the case of branch retinal vein occlusion, macular oedema occurs when the temporal vein draining the macula is occluded.
- Other causes of CMO include inflammatory diseases (uveitis, scleritis, birdshot chorioretinopathy, toxoplasmosis), various types of retinal vascular disease (idiopathic retinal telangiectasia, radiation retinopathy), retinal dystrophies (such as retinitis pigmentosa) and drug-induced (such as can occur with topical adrenaline 2%, particularly in patients without a lens). It can also occur following injury to the eye and in association with choroidal tumours.
Macular oedema can also occur in the context of diabetic retinopathy. If it occurs in a critical part of the macula or reaches a particular size, it is referred to as clinically significant macular oedema (CSMO). It occurs as a result of increased vascular permeability due to histological changes, so resulting in a compromise of the blood-retinal barrier and leakage of plasma constituents into the surrounding area. The oedema can be focal or diffuse - its nature will guide treatment. See separate article Diabetic Retinopathy and Diabetic Eye Problems for more detail.
The third group of patients prone to macular oedema are those suffering from certain forms of age-related macular degeneration (AMD): exudative ('wet') AMD. This gives rise to formation of choroidal neovascular membranes which leak fluid and blood under the retina, so resulting in macular oedema. See separate Age-related Macular Degeneration article for more detail.
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- Cystoid macular oedema (CMO) - Irvine-Gass syndrome is rare in modern uncomplicated cataract surgery, occurring in about 1% of cases in a very mild form (in the past, old and now largely discontinued techniques were associated with up to 20% of patients developing CMO). More complex surgery results in higher rates (epidemiological data report very mixed figures) as does the presence of pre-existing inflammation. The incidence of other causes of CMO varies according to the specific pathology but is not generally very common.
- Clinically significant macular oedema (CSMO) - if the diabetes is undiagnosed and untreated, there is a 25-30% chance of developing CSMO: this drops by half in treated patients. It is more likely to occur in patients over 60 years old with systemic vascular diseases such as hypertension or diabetes.
- Wet age-related macular degeneration (AMD) - AMD tends to occur in patients aged over 60 and is the leading cause of blind and partial sight certification in the over-65s. Wet AMD occurs in about 10% of all AMD cases.
The exact nature of presentation will vary with the underlying pathology but, essentially, if there is no pre-existing disease, patients will complain of a painless impairment of central vision ± a positive scotoma (a black spot within the field of vision). The visual decline is typically in the region of 6/12 to 6/60. Individuals with Irvine-Gass syndrome usually have a good visual acuity initially, followed by a gradual blurring. Occasionally, the condition may be asymptomatic. Clinically significant macular oedema (CSMO) may be completely asymptomatic and only be picked up in the diabetic screening clinic/unit. Patients with age-related macular degeneration (AMD) may complain of visual distortion (particularly of straight lines) and a few complain of blue-yellow colour blindness.
The normal macula: what am I looking for?
The macula lies about 2 disc diameters temporally (laterally) to the disc itself. It may be seen as a slightly darker area than the surrounding retina (more so in darker people) with blood vessels arching over and under it but not on top of it. Careful examination will reveal the foveal reflex, a small yellow-white shiny reflection in the centre of the macula - this is the fovea centralis.
Identifying macular oedema
It is not possible to diagnose macular oedema without the help of a slit lamp. A clue might be the loss of the foveal reflex compared to the fellow eye. In wet AMD, there may also be an associated bleed, seen as a well-demarcated deep red patch over the macular area. Even if the view is limited, the history and an abnormal Amsler grid will raise suspicions and should prompt referral.
This is a useful simple tool that can help screen for macular disease and that the patient can use at home to monitor progression. It consists of a piece of paper on which a 10 cm x 10 cm box is printed, subdivided into 20 x 20 smaller squares and with a black dot in the centre. The patient is asked to wear any corrective lenses that they usually wear, hold the chart 33 cm away (arm's length) and cover one eye. They must then fix their gaze on the central dot. They are asked if they can see the four corners of the box. They are then told to comment on how straight the lines of the grid are and to draw over them as they see them in the parts that seem curved. Finally, they are asked to outline any areas missing within the box. This should be repeated for the fellow eye. This gives a reasonable indication of macular function.
Once macular oedema is confirmed, the cause is likely to be one of those outlined above. In the young (typically type A personality male) patient, it could also be confused with central serous chorioretinopathy, a generally self-limiting condition which typically arises in times of acute stress, whereby there is a localised accumulation of fluid within the retina.
Macular oedema is usually diagnosed on slit-lamp examination. These days, it is often confirmed with optical coherence tomography (OCT), which is a sort of visual biopsy obtained in a similar fashion to an ultrasound scan but using light waves. It is a painless diagnostic imaging modality that is performed in the outpatient setting, with the patient looking into the OCT machine for a few moments. OCT is useful both to confirm diagnosis (newer software is now able to distinguish between different patterns of cystoid macular oedema (CMO) associated with different underlying pathology) and to monitor progress. Fluorescein angiography may also be required to further refine the diagnosis and guide management
The management of macular oedema depends on its aetiology and extent. Many causes of macular oedema respond to treatment of the underlying condition (eg cystoid macular oedema (CMO) associated with cytomegalovirus (CMV) retinitis is treated by managing the retinitis with antiviral agents).
- Irvine-Gass syndrome is typically managed using a combination of topical steroids (eg prednisolone 1%) and topical non-steroidal anti-inflammatory drugs (NSAIDs) (eg ketorolac) over several months, although the evidence behind this is actually quite poor. Persistent oedema may warrant acetazolamide or a topical injection of triamcinolone. Very occasionally, these patients need further surgery (to remove the vitreous).
- Some patients with retinal vascular disease may benefit from laser photocoagulation and all patients with inflammatory disease will need anti-inflammatories to control the underlying disease.
- More recently, the benefits of anti-vascular endothelial growth factor (anti-VEGF) treatment has been explored in CMO secondary to central retinal vein occlusion: early results are promising but the long-term effects/benefits are not yet known and the outcome of several trials is awaited. Those that have been published have shown mixed results.
- Clinically significant macular oedema (CSMO):
- Almost all CSMO patients need laser photocoagulation but some argue that the decision to treat is not always clear-cut (eg asymptomatic patients with CSMO but no visual loss). This is a damage limitation exercise in that it reduces the risk of visual loss (by 50%) rather than restoring vision, which only happens in a small number of patients. There is photocoagulation of specific vessels (focal treatment) or using a grid pattern of laser burns spaced 1 spot-width apart over the affected area where specific leakage points cannot be identified, sparing the macular area.
- Newer treatment modalities are more fully discussed in the separate Diabetic Retinopathy and Diabetic Eye Problems article, but include intravitreal triamcinolone acetonide, intravitreal anti-VEGF agents, and there are ongoing studies looking at other possibilities too.
- Rigorous systemic management of the diabetes and any concurrent hypertension and hyperlipidaemia is essential in these patients, as demonstrated by a number of respected studies (described in the article dealing with diabetic retinopathy).
- Occasionally, certain patients benefit from surgical removal of the vitreous.
- Wet age-related macular degeneration (AMD):
- Some of these patients respond to photodynamic therapy if they fulfil certain clinical criteria (the first being the need to have a vision of 6/60 or greater). Unfortunately, only a minority of patients will fulfil these standards; treatment is known to be ineffective in patients who don't meet these criteria.
- Anti-VEGF treatment is now becoming standard since it was endorsed by the National Institute for Health and Clinical Excellence (NICE) in 2008. This is more fully discussed in our separate article Age-related Macular Degeneration.
If the oedema is prolonged, scarring or a hole can eventually ensue.
- Cystoid macular oedema (CMO) - this depends on the aetiology but in uncomplicated cases (such as following cataract surgery), recovery is usually good after several months: 90-95% of these patients can expect a final visual acuity of 6/12 or better within three to 12 months of their operation. Severe cases can result in more permanent visual loss. In other cases where irreversible processes have occurred (such as in central retinal vein occlusion), the outlook may be very bleak with little or no chance of recovery. Where there are inflammatory processes, the duration and severity of the condition will determine overall outcome. Treatment modalities that have been tried in these patients include laser treatment, intravitreal steroids and more recently, intra-vitreal anti-vascular endothelial growth factors (anti-VEGFs).
- Clinically significant macular oedema (CSMO) - improvement of visual function is rare (where deterioration has occurred). At best, treatment aims to arrest deterioration.
- Wet age-related macular degeneration (AMD) - these patients tend to have a poor outcome, even with therapy (which is long, may be painful and is very expensive) - hence, the small number of patients treated. Most experience a sudden and rapid deterioration in visual function which is irreversible. Vision never fully disappears and peripheral vision will remain normal in the absence of concurrent disease.
Preoperative NSAIDs are sometimes given to high-risk patients in cataract surgery. Good glycaemic control, blood pressure and cholesterol control may stall the process in diabetic patients and any progression of the condition once it has developed can be arrested with laser and other treatment modalities. These patients need intensive steroid cover in order to minimise the risk. Good diabetic control and regular screening to detect clinically significant macular oedema (CSMO) are the best approach to minimise its effects. Patients with a known diagnosis of age-related macular degeneration (AMD) are often issued with an Amsler grid in order to try to catch any macular changes early. AMD patients with 'wet' macular disease may be monitored in outpatients. AMD patients may also be advised to take multivitamin supplements to prevent progression of the disease in the fellow eye. The use of these supplements remains somewhat controversial and is more fully discussed in the AMD record.
Further reading & references
- American Academy of Opthalmology. Basic and Clinical Science Course 2010-2011. Section 12: Retina and Vitreous
- Denniston AKO, Murray PI. Oxford Handbook of Ophthalmology (OUP), 2009.
- Telander DG et al, Macular Edema, Pseudophakic (Irvine-Gass), eMedicine, Apr 2010
- Jackson TL; Moorfields Manual of Ophthalmology, Mosby (2008)
- Kanski J. Clinical Ophthalmology, A Systematic Approach, 5th ed. Butterworth Heinemann (2003)
- Roth DB; Nonpseudophakic Cystoid Macular Edema, eMedicine, Apr 2010
- Mavrikakis E et al, Macular Edema in Diabetes, Medscape, Oct 2012
- Braithwaite T, Nanji AA, Greenberg PB; Anti-vascular endothelial growth factor for macular edema secondary to central Cochrane Database Syst Rev. 2010 Oct 6;(10):CD007325.
- Moradian S, Faghihi H, Sadeghi B, et al; Intravitreal bevacizumab vs. sham treatment in acute branch retinal vein Graefes Arch Clin Exp Ophthalmol. 2011 Feb;249(2):193-200. Epub 2010 Aug 18.
- Chang LK, Spaide RF, Klancnik JM, et al; Longer-term Outcomes of a Prosepctive Study of Intravitreal Ranibizumab as A Retina. 2011 Feb 11.
- Mohamed Q, Gillies MC, Wong TY; Management of diabetic retinopathy: a systematic review. JAMA. 2007 Aug 22;298(8):902-16.
- Parravano M, Menchini F, Virgili G; Antiangiogenic therapy with anti-vascular endothelial growth factor modalities Cochrane Database Syst Rev. 2009 Oct 7;(4):CD007419.
|Original Author: Dr Olivia Scott||Current Version: Dr Olivia Scott|
|Last Checked: 18/03/2011||Document ID: 1298 Version: 22||© EMIS|
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