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The retina is made up of a sensory layer containing the photoreceptors, a middle layer containing several types of other nerve cells, and an innermost layer comprising the ganglion cells which receive the transmit the received impulses through the optic nerve.
The retina lies upon the retinal pigment epithelial (RPE) which contains cells rich in melanin. This layer separates it from the choroid, a dense plexus of blood vessels which supports and nourishes the sensitive structures in the eyeball. The melanin absorbs any light which escapes the sensory layer, prevents or minimizes backscattering of light and renews the photoreceptor pigments which are bleached each time they respond to incoming light photons. It also ensures a quick turnover of the photoreceptor disks which is essential for good vision.
80 percent of the eye is filled with the gel-like vitreous body, which gives the eye its round contour. This is crisscrossed by millions of very fine connective tissue fibers, which are attached more or less loosely to the retinal surface. In most patients, the vitreous contracts with age. In areas where the fibers are firmly attached, the retina tears due to the pulling away of the vitreous. This creates a retinal hole.
Thus retinal breaks are holes in the retina that occur mostly when the vitreous body in front of the retina contracts and tugs on it. This leads to seepage of fluid underneath the retina through the break. As a result the retina in that area detaches from the underlying RPE. This is also called a rhegmatogenous retinal break. It is seen in a quarter of patients who present with a posterior vitreous detachment. This shoots up to two-thirds if the patient also has associated vitreous hemorrhage.
Other reasons for a retinal break to occur include:
Retinal breaks may be peripheral or macular.
Peripheral breaks include:
Operculated breaks where a small piece of retina is so firmly attached to the vitreous fibers that it is pulled right off, covering a small hole.
Flap tears, where a U-shaped or horseshoe tear occurs in the posterior part of the retina. This is the most likely to lead to fluid collection under the sensory layer and later to retinal detachment. It is often associated with local vitreous traction pulling up a flap of the retina.
Atrophic holes, which are the most common types. These are holes extending through the full thickness of the retina. It is usually round and the surrounding area may or may not be pigmented. It is due to poor vascular supply and in degenerative conditions of the retina such as lattice degeneration.
The most early and common symptom when a retinal break occurs is the loss of peripheral vision in that area, as a result of the retinal detachment. The loss of peripheral vision in that area, however, is a subtle sign in most cases and is usually missed by the patient. Patients also report the presence of floaters, or flashes of light. Floaters are small black specks or streaks that appear in the field of vision and dart about with eye movements. They are actually shadows cast upon the retina by organized blood, coarse intravitreal fibers or cell clumps within the vitreous and are of no particular significance by themselves.
Retinal breaks should be looked for in every case of posterior vitreous detachment. The vitreous should be carefully examined, as well as the peripheral retina. Early detection is important to prevent them from developing into retinal detachment and associated vision loss.
Treatment depends on the type and location of the break, the other findings noted, and the presence of symptoms or risk factors. Symptomatic flap tears carry the greatest risk for progression to retinal detachment. Cryotherapy and photocoagulation are currently employed methods to seal retinal breaks. Both these methods induce fibrosis around the treated area, holding the retina firmly to the underlying RPE.
Written by Yolanda Smith, BPharm