In the normal eye, the retina lies in apposition to the underlying tissues through a combination of osmotic forces and a weak extracellular matrix adhesion between the photoreceptor outer segments and the microvilli of the retinal pigment epithelium. Maintenance of the precise extracellular composition requires integrity of the vasculature of the choriocapillaris (tight junctions making up the “blood-ocular barrier”).
Detachments of the retina are categorized as either those associated with a retinal tear (rhegmatogenous) or those which are serous or exudative (non-rhegmatogenous). Both forms can be caused by many conditions including systemic diseases as well as those limited to the eye.
Causes of Retinal Detachment
|Inflammation-induced vitreal traction bands|
|Peripheral cystic retinal degeneration|
|viral (FeLV, FIV, FIP)|
|secondary (multiple myeloma, lymphosarcoma)|
In some cases, the diagnosis of retinal detachment is made by direct visualization of the retina. In other cases, opacities (cataract, hemorrhage) may prevent direct visualization and ultrasonography may be necessary.
Treatment is directed at 1) medical therapy to promote resorption of the subretinal fluid and 2) mechanical attachment of the retina (retinopexy).
Accurate diagnosis of a primary condition, if any, allows for specific medical therapy. Systemic hypertension is the most common cause of serous retinal detachment in cats (Hypertensive retinopathy). Management of high blood pressure through diet and anti-hypertensive medications often results in retinal re-attachment and restoration of vision in these cases. Retinal detachments caused by idiopathic or immune-mediated conditions require the use of non-specific medical therapy. systemic corticosteroids and diuretics are of value in promoting resorption of the subretinal fluid. These medications are of little value, however, in cases where a retinal tear exists as there is continued fluid seepage from the vitreous compartment into the open subretinal space. In such cases, particular when the tear is located superiorly, gravity will encourage progression of the detachment.
Retinopexy procedures utilize cryotherapy or laser treatment to form adhesions between the retina and the underlying retinal pigment epithelium and choroid. These procedures are of particular value in “sealing” the area surrounding a retinal tear. They cannot attach an area of the retina that is completely separated, but they can prevent progression of rhegmatogenous detachments. The diode laser can be applied directly to the sclera for treatment of the peripheral retina. During peripheral laser retinopexy, the red He-Ne aiming beam can be directly visualized through the pupil, allowing precise localization of the treatment sites. Treatment of more centrally located areas is performed using a laser delivery system through a specially modified ophthalmoscope.
Retinal detachment can be seen as one of the most frustrating complication of surgical cataract extraction. Although they occur rarely, these detachments are often associated with retinal tears, making them refractory to medical management. many of the breeds in which inherited cataracts are seen are also at greater risk for progressive vitreal degeneration which can weaken the retinal/RPE attachment, predisposing to retinal detachment. The most notable example of this is the Shih Tzu, where spontaneous retinal detachment occurs as a sequella to vitreal degeneration.
Surgical extraction of a luxated lens often also requires removal of some of the vitreous which can predispose to retinal detachment. Lens-induced uveitis, which is often seen in eyes where cataract surgery is contemplated, is also considered a risk factor for retinal detachment. Because the density of the lens opacity may prevent direct visualization of the retina, ocular ultrasonography is used to detect a pre-existing retinal detachment prior to surgery.
In patients considered to be at risk for retinal detachment, a prophylactic laser retinopexy is performed. Following the surgical lens extraction procedure, a 360 degree peripheral laser retinopexy is performed involving 150-250 sites arranged in one or two rows located 6-8 mm behind the limbus.
Veterinary Vision acknowledges the support of Iridex Iris Medical, Inc. in providing the equipment and technical support which has made possible the development of many of the techniques described in this article.