Rhegmatogenous retinal detachment


Rhegmatogenous retinal detachment

Description, Causes and Risk Factors:

Abbreviation: RRD.

Rhegmatogenous retinal detachment is a potentially blinding ophthalmic pathology caused by a separation of the neurosensory retina (NSR) from the underlying retinal pigment epithelium and the accumulation of fluid within this potential space.

The majority of RRD are associated with retinal tears which in turn are induced by a vitreous detachment. It is estimated that 95% of retinal tears occur at the time of a vitreous detachment and so the diagnosis of a vitreous detachment is an important one. Other retinal breaks that can progress to a RRD include atrophic retinal holes, retinoschisis, cystic retinal tufts and rarely macular holes.

It is responsible for up to 2% of blind and partial sight registrations in Ireland, Scotland and south west England. The mainstay of RRD treatment is surgical, accounting for an important proportion of ophthalmic hospital in-patient admissions at an annual cost of over £1.3 million in the UK. The principles defining an epidemiology study are the careful delineation of the study population from which cases are derived and the effort to ascertain every eligible case from the study population. To date there have been no large-scale systematic epidemiology studies of RRD in Scotland. Previous population based estimates of the incidence of RRD have varied considerably, with overall annual incidence rates reported between 5-17.9 per 100,000 of population. Based on these previous reports, we estimate that there are between 500-600 new cases of RRD in Scotland annually.

Three conditions must be satisfied to cause RRD: vitreous liquefaction, tractional forces producing a retinal break and an open retinal break allowing fluid to gain access to the sub-retinal space. The subtype of RRD is described according to the type of retinal break causing the detachment and may be classified as follows:

    Horse-shoe shaped tear: This refers to tear in the neurosensory retina (NSR) due to a persistent site of vitreo-retinal traction during a posterior vitreous detachment.

  • Giant Retinal Tear: These are defined as circumferential retinal breaks of 90 degrees or more. The tear is usually along the posterior margin of the vitreous base, may have a rolled edge and rarely may occur at the anterior margin in the ciliary epithelium.

  • Dialysis: Defined as circumferential tears along the ora serrata with persistent vitreous attachment to the posterior retina (i.e., No posterior vitreous detachment).

  • Round Hole: This refers to an avulsed or operculated area of peripheral retina induced by a complete or localised vitreous separation. It may also refer to atrophic retinal holes associated with areas of pigmentation or peripheral retinal degeneration.

  • Retinoschisis: This describes a degenerative process causing a splitting of the retinal layers. If retinal breaks occurs in both the outer and inner leaves of a retinoschisis causing a progressive extension of sub-retinal fluid requiring intervention this is classified as a retinoschisis detachment.

RRD may occur in the presence of conditions predisposing to a retinal break:

    Age.

  • Lattice degeneration.

  • Aphakia (no crystalline lens).

  • Age-related retinoschisis.

  • Previous retinal break.

  • Marfan's syndrome.

The genetic risk of RRD has been investigated through family linkage studies and twin reports. It has also been noted that familial occurrence of RRD is a risk factor for its' development, with a risk ratio of 2.6 for cumulative lifetime risk of RRD in relatives of subjects with RRD compared to relatives of those without RRD. Recently, genome-wide association (GWAS) studies have become established as powerful tools in identifying common genetic variants that predispose to common, complex disease. These case-control studies seek to characterize DNA nucleotide polymorphisms in a large number of cases and disease-free controls to determine if certain polymorphisms are associated with the disease phenotype. To date no GWAS have been conducted on rhegmatogenous retinal detachment. Our study will establish an important resource for further exploration of the genetic aetiology of this condition.

Symptoms:

Signs and symptoms may include:

    Cell and flare may be seen in the anterior chamber of eyes with a rhegmatogenous retinal detachment (RRD).

  • A retinal break in the shape of a horseshoe or flap is often present. Of all RRDs, 50% have more than 1 break. Of all breaks, 60% are located in the upper temporal quadrant, and 15% are located in the upper nasal quadrant. Another 15% are in the lower temporal quadrant, and 10% are in the lower nasal quadrant.

  • Chronic RRD may present with retinal thinning, intraretinal cysts, subretinal fibrosis, and demarcation lines. These lines are usually at the junction of attached and detached retina. Even though they represent areas of increased retinal adhesion to the RPE, it is not uncommon for subretinal fluid to spread beyond the lines.

  • The intraocular pressure is usually lower in the eye with a RRD than in the fellow eye; this is usually reversed by retinal reattachment. In certain cases, the intraocular pressure may be higher than in the fellow eye.

  • Pigment in the anterior vitreous (tobacco dusting or a Shaffer sign) is usually present.

  • Once the retina becomes detached, it assumes a slightly opaque color secondary to intraretinal edema. It has a convex configuration, has a corrugated appearance, and undulates freely with eye movements unless severe proliferative vitreoretinopathy (PVR) is present.

Diagnosis:

On certain occasions, the media may not be clear, impairing a thorough retinal examination with the binocular indirect ophthalmoscope. An ultrasound is a useful adjunct in these situations.

Ultra-high-frequency sounds travel to the back of the eye as the probe emits them. Once a structure is contacted by the sound waves, the sound wave is attenuated and reflected back to the probe. The pattern of these waves is specific for certain tissues. Thus, localization and tissue characterization is possible using this technique. Typically, an A scan and a B scan are obtained. For instance, retinal tissue usually shows a large spike in the A scan, reflecting an increased acoustic density of the tissue. The B scan shows a composite picture of the globe and its intraocular contents.

Sometimes, it may be difficult to differentiate a retinal detachment from a thickened, partially detached posterior hyaloid. In this case, A-scan and B-scan findings often overlap. Tissue mobility during scanning may help to differentiate the two. Usually, a RRD has a characteristic undulating motion after a sudden saccade, whereas a thickened posterior hyaloid moves in a brisker manner but with less excursion.

Other Tests:

    Fluorescein angiography (FA): Cystoid macular edema may complicate the postoperative course of an eye that has undergone retinal reattachment surgery. FA is a useful adjunct in helping to diagnose this condition.

  • Optical coherence tomography (OCT): Occasionally, certain eyes appear to have complete retinal reattachment, but the visual acuity recovery appears to be incomplete or delayed. OCT helps to reveal subfoveal fluid in these eyes.

  • Electroretinogram (ERG): When a patient presents with a dense vitreous hemorrhage or a cataract that precludes direct visualization of the retina, an ultrasound of the posterior pole is indicated. Sometimes, differentiating a RRD and a thickened posterior hyaloid that is partially detached using ultrasound is difficult. In these circumstances, an ERG is a useful adjunct in the evaluation of a patient suspected of having a RRD. If a good response from the ERG is obtained, the retina is probably attached. If the electric response from the retina is attenuated to a great degree, the retina is probably detached.

Treatment:

Regardless of the surgical technique chosen, the surgical goals are to identify and close all the breaks with minimum iatrogenic damage. Closure of the breaks occurs when the edges of the retinal break are brought into contact with the underlying RPE (retinal pigment epithelium). This is accomplished either by bringing the eye wall closer to the detached retina (a scleral buckle) or by pushing the detached retina toward the eye wall (intraocular tamponade with a gas bubble). Sealing of the breaks is accomplished by creating a strong chorioretinal adhesion around the breaks; this may be completed with diathermy, cryotherapy, or laser photocoagulation.

During diathermy, an alternating electrical current of 13.56 MHz is generated. As the current passes through the tissue, resistance of the tissue gives rise to heat. This heat coagulates the tissue. Diathermy produces an adequate RPE adhesion, but it produces immediate scleral shrinkage with subsequent scleral necrosis. This leads to complications during reoperations and an increased rate of scleral abscess formation. Diathermy is generally used during implant procedures.

Cryotherapy avoids all the complications of diathermy. However, it breaks down the blood-ocular barrier and may cause dispersion of RPE cells into the vitreous cavity, which may contribute to PVR (proliferative vitreoretinopathy). Following cryotherapy, the retinal RPE adhesion is usually weaker during the first week, but, by the end of the second week, the adhesion attains its strongest strength.

Laser photocoagulation causes the least morbidity. However, it requires the retina to be flat over the RPE before a chorioretinal adhesion can be formed. The adhesion attains its maximum strength at 7 days.

Surgical Options:

There are three approaches to surgical treatment, the first two of which are the most commonly used:

    Scleral buckle - a silicone sponge or solid silicone explant is placed on the outside of the globe at the site of retinal breaks, indenting the sclera and so bringing this into apposition with the loose retina. The breaks themselves are treated with laser or cryotherapy. The idea is to close off the breaks and to reduce any associated vitreal traction. The explants may be short stumps placed locally or longer structures encircling the circumference of the globe. The choice depends on the nature of the breaks.

  • Vitrectomy - the vitreous may be removed in the case of a tractional retinal detachment (TRD). This technique is also now increasingly used in rhegmatogenous retinal detachment, although there is considerable inter-surgeon variation.

  • Pneumatic retinopexy - a gas bubble (sometimes a silicone bubble) is injected inside the globe, over the site of the break (which has either previously been repaired with cryotherapy or is subsequently repaired with laser therapy) and pushes the flaps of retina against the periphery. If it stays in position, it permits the subretinal fluid to be resorbed over 24-48 hours. The bubble itself will very gradually be resorbed over weeks/months. This procedure is favored in North America and less commonly used in the UK. It is only suitable for a minority of straightforward cases.

NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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