miércoles, 13 de febrero de 2019

Submacular Hemorrhage (SMH)

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By Liji Thomas, MDReviewed by Susha Cheriyedath, M.Sc.

Submacular hemorrhage (SMH) is a term which describes a condition characterized by the presence of blood in the potential space between the retinal pigment epithelium and the retinal layer. The blood comes from fragile new vessels in the choroidal layer, formed in the process of choroidal neovascularization CNV). The patient with SMH suffers acute and painless visual distortion with eventual loss of central vision.

In the majority of patients, CNV is due to age-related macular degeneration. Other causes include:

High myopia
Scars following inflammatory conditions
Trauma to the eye
Angioid streaks
Histoplasmosis of the eye
Choroidal vascular conditions of unknown origin

Symptoms

Submacular hemorrhage is a sight-threatening disorder. When it occurs, the patient may report that there is a sudden blurring of vision, as well as waviness of lines. This phenomenon is called metamorphopsia, and occurs in the center of the visual field, or, in other words, with respect to the object one is directly looking at.

Complications

Following a hemorrhage into the submacular space, the outer layers of the retina deteriorate and break down speedily. This is because of:

Disruption of the connections between the RPE and the photoreceptor cells inhibiting normal diffusion between them, culminating in rapid photoreceptor atrophy
Contraction of the organizing clot leading to shear stress on the attached retina and the formation of retinal scars
The toxic effects of the iron released from the red cells breaking down in the clot
Other toxins released from stressed tissue
Migration of cells into the subretinal space with subsequent proliferation
Formation of a proliferative fibrovascular membranous layer over the retina

Treatment

A submacular hemorrhage is an emergency to be treated by removal of the clot on an urgent basis. The techniques in common use include:

Manual clot removal following vitrectomy
Vitrectomy with recombinant tissue plasminogen activator (r-tPA) injection into the intravitrealspace to dissolve the clot, and placement of intraocular gas to displace the clot
Removal of the membrane formed by the new vessels, done alone or as part of the above procedure
Instillation of gas to displace the clot, without r-tPA injection
Injection of r-tPA subretinally along with the instillation of perfluorocarbon liquid to displace the SMH into the vitreous space for manual removal
Adjuvant therapy with anti-VEGF (vascular endothelium growth factor) injection to discourage neovascularization and subsequent bleeds, and maintain the improvement due to clot displacement
Focal photocoagulation by laser is used to seal the bleeding submacular vessels

Prognosis

The prognosis of a submacular hemorrhage depends upon the size and extent. A large SMH is often the cause of irreversible vision loss, with or without treatment. If the SMH is an extension of a subretinal hemorrhage, it is often treatable, but complete recovery of normal vision is difficult to achieve. When, as is very often the case, the SMH is a complication of the exudative (“wet”) form of AMD, half of these patients will develop another SMH in less than 3 years from the onset of the first.