Retinal macroaneurysms are acquired, usually round dilations of the large arterioles of the retina. They are commonly associated with macular exudation and hemorrhage, which may result in decreased visual acuity. A 10% incidence of bilateral disease exists, and multiple aneurysms in the same eye occasionally are seen. (See the image below.) [1, 2, 3]
Formation of retinal macroaneurysms is associated with systemic hypertension (in approximately 75% of patients) and atherosclerotic disease, but serum lipid abnormalities also have been reported. About 10% of patients have focal arterial wall atheroma occurring at defects in the wall, which may be sites at risk for aneurysm formation.
The female-to-male ratio for macroaneurysms is 3:1. They occur most commonly in the sixth to seventh decade and are rare before age 60 years.
Most patients with macroaneurysm present with sudden onset of painless vision loss in 1 eye. If the central macula is spared, however, the patient may be asymptomatic. Aneurysms that present without exudation or hemorrhage are asymptomatic.
The visual prognosis is excellent for many patients with macroaneurysm. The natural history of these lesions suggests that most close spontaneously, with restoration of near-normal vision.
In some patients, the Valsalva maneuver may be associated with an increased risk of hemorrhage. However, although reducing the risk of the Valsalva maneuver in patients with active, pulsatile retinal macroaneurysms may be beneficial, this has not been proven to reduce the incidence of hemorrhage in these patients.
Vision loss from macular edema due to chronic exudation is well documented in many patients, and laser treatment may be appropriate. Vision loss resulting from retinal macroaneurysms usually results from scarring in the macula due to either chronic edema or hemorrhage. 
Additional complications of macroaneurysm development include retinal and subretinal hemorrhage, as well as epiretinal membrane formation.
A study suggests that patients with preretinal hemorrhage or vitreous hemorrhage due to retinal macroaneurysms have a good visual prognosis. In contrast, the visual prognosis is poor in patients with submacular hemorrhage.
The formation of a macular choroidal neovascular membrane and retinal angiomatous proliferation in a consolidating exudate, following treatment of a retinal macroaneurysm, have been reported by this author. 
Vascular Signs and Sites of Occurrence
Macroaneurysms more commonly affect the right eye than the left. Aneurysmal dilation of the retinal arterioles occurs, usually at the site of vessel bifurcation or arteriovenous crossing in the major branch retinal arteries. The supertemporal artery most commonly is involved. However, macroaneurysms also have been reported in cilioretinal arteries and on the optic nerve head. Occasionally, multiple aneurysms are present.
Usually, leakage of protein-rich serum occurs, leading to circinate exudation and macular edema. Serous retinal detachment can occur.
Bleeding is a common complication of aneurysm formation and can occur beneath the retina, the retinal pigment epithelium (RPE), or the internal limiting membrane (ILM), or into the vitreous. Pulsatile flow occasionally is observed but does not necessarily indicate a higher risk of hemorrhage.
The differential diagnosis of macroaneurysm includes the following:
Leber miliary aneurysms
Laboratory, Imaging, and Histologic Studies
Serum lipids may be elevated. Blood glucose is likely to be in the reference range, but a glucose test may nonetheless be indicated in order to exclude undiagnosed diabetes in patients with exudative retinopathy in which the etiology is unclear.
B-scan (and possibly A-scan) ultrasonography may be indicated to rule out a choroidal mass or hemorrhagic retinal detachment in cases of hemorrhagic RPE detachment that may simulate a choroidal melanoma or a dense vitreous hemorrhage (which obscures visualization of the posterior pole).
Microvascular abnormalities (eg, widening of the periarterial capillary free zone, capillary dilation, nonperfusion, intra-arterial collaterals) have been identified. Histologic studies of macroaneurysms show a break in the arterial wall, surrounded by a laminated layer of fibrin-platelet clot and blood. Lipid-laden macrophages, hemosiderin, and fibroglial reaction are also observed.
Fluorescein Angiography and Optical Coherence Tomography
Fluorescein angiography is the most helpful imaging study for the diagnosis of macroaneurysm. Saccular dilation of the arteriolar wall is diagnostic of the disease. Angiography is particularly important in making the diagnosis when hemorrhaging (which obscures the vasculature) occurs.
Late fluorescein leakage from within the areas of hemorrhage is characteristic of macroaneurysms and may assist in the diagnosis when the vasculature is not visible on direct examination. (See the images below.)
Recent reports have shown that optical coherence tomography (OCT) of the retinal vasculature can be used to identify and quantify arterial dilation in these patients. 
No general consensus exists about laser treatment of retinal macroaneurysms. The natural history of the disease suggests that spontaneous closure is common. Treatment may not be indicated for most patients.
Moreover, laser treatment may not improve the visual outcome, even when closure is successful, because of chronic edema and macular scarring.
The most frequently cited indication for laser photocoagulation of a macroaneurysm is persistence or progression of macular exudation. The current recommendation for photocoagulation of macroaneurysms is the use of the argon green or yellow dye laser for direct photocoagulation of the lesion.
Some authors have recommended indirect treatment to minimize the risk of arteriolar occlusion and hemorrhage, but little rationale to this approach exists, since the site of leakage is the macroaneurysm. Others recommend low power settings sufficient to create a light to moderate burn intensity, using a large spot size (500µm) and long-duration (0.5s) pulses directly on the lesion.
In the setting of dense subhyaloid hemorrhage, YAG-laser hyaloidotomy has been performed to release the sequestered blood into the vitreous cavity.
Release of blood that is sequestered over the macula may reduce the risk of macular scarring and epiretinal fibrosis. This procedure is controversial, however, because of the risk of macular injury and vitreous hemorrhage.
Complications of laser treatment can include macular infarction from retinal arteriolar occlusion and laser-induced hemorrhage or retinal damage. Increased retinal exudation and scarring with subsequent retinal traction are also possible. However, a recent study of outcomes in patients who have undergone conservative treatment (observation only), laser treatment, or vitrectomy indicate that visual outcomes are good in any of these treatment regimens. 
In rare settings in which vitreous hemorrhage is present and the etiology of bleeding is unclear, vitrectomy may be indicated. However, removal of dense subretinal hemorrhage is very controversial and has the potential to cause many serious complications. 
The goal is to remove the extravasated blood and to assist in the diagnosis and possible treatment. Pneumatic displacement of premacular hemorrhages using SF6 gas has also been reported.