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Forgot password? Review as guest. Vitreoretinal Disease. Retinal detachments are also treated symptomatically. Systemic drugs, such as corticosteroids and diuretics, may hasten the reabsorption of the subretinal fluids, and reapposition of the neurosensory retinal layers and the retinal pigment epithelium.
The broad objective for this type of retinal detachment surgery is the identification of the retinal breaks and sealing these breaks. Detection of retinal breaks in small animals requires meticulous examination of the retina by ophthalmoscopy usually the indirect method. Mydriasis is necessary to observe as much as possible of the peripheral retina. Often the dog requires sedation to accommodate the time for this examination and the scleral depression. Postoperative capsular and pupillary opacities after cataract surgeries may limit fundic observations.
Scleral depression can be achieved under topical anesthesia with a scleral depressor instrument, Jameson muscle hook or a moist cotton swab. The scleral depressor is used to indent the globe a few millimeters posterior to the limbus while simultaneously performing indirect ophthalmoscopy. Most retinal breaks holes and tears occur in the peripheral retina. Once the fundoscopic examination has been performed and any retinal breaks identified and localized, retinal surgery may be indicated. The general principles for the surgical treatment of rhegmatogenous retinal detachments are summarized in Box Once the retinal traction is removed and the retinal breaks are sealed, normal physiologic function of the retina may resume with the pigmented epithelium to evacuate the subretinal fluids, and eliminate any space between the neurosensory retina and the retinal pigment epithelial layers.
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Box Closure of retinal break: By diathermy, cryotherapy, or laser. Collapse of the space between the separated retinal layers:.
Ophthalmology | Vitreoretinal Disease
Development of focal chorioretinitis that eventually resolves to form scar tissue that adheres to the retinal layers within the detached area and, most importantly, around the retinal break. Modified from Smith PJ Surgery of the canine posterior segment. In: Gelatt KN ed.
Veterinary Ophthalmology, 3rd edn. Lippincott, Williams and Wilkins, Baltimore, p — Additional invaluable diagnostic procedures for small animals are electroretinography and ultrasonography. Electroretinography may provide information as to the viability of the retina, and for detecting retinal detachments. Ultrasonography is used particularly to evaluate the posterior segment in which visualization is incomplete because of a small pupil, or lens or vitreal opacities Fig.
Note also the opacities within the vitreous.
For optimal results in vitreoretinal surgeries, a considerable investment in training and instrumentation is necessary. Basic ophthalmic instruments are necessary to perform the surgical approach for retinal detachments. These instruments are necessary to perform the conjunctival peritomy and periocular surgery to isolate and sometimes transect the extraocular muscle insertions.
In addition, several of the instruments are essential. Posterior vitreous cutter, light source, IOP control, and wet-field cautery are necessary. The Machemer lens rests on the cornea and provides irrigation to the cornea, and a wide field of vision and magnification. To inject silicone oil, either a large bore high viscosity cannula with a Luer-lock syringe for manual injection or a special syringe pump and high-viscosity injection, are necessary. The perfluorocarbon gases are used to manipulate and flatten retinal detachments during pars plana retinal detachment surgeries.
They are biologically inert, clear optically, immiscible with water, and have a higher specific gravity than saline. Of the perfluorocarbon gases in use, perfluorooctane, perfluorotributylamine, perfluorodecalin, and perfluoroperhydrophenanthrene, only the first two gases have been used in the dog. Approximately twice as heavy as water, these gases can very effectively tamponade and flatten the retina intraoperatively, and displace subretinal fluid anteriorly from peripheral retinal breaks into the vitreous. They are removed after retinopexy because of potential retinal toxicity, and replaced with silicone oil which will remain in the eye postoperatively for several months.
The silicone oils are different molecular weights of polydimethylsiloxane. Of those available, the medical grade centistoke SiO is the most frequently used in the dog. With a specific gravity of 0. In aphakic and pseudophakic dogs after SiO injection into the vitreal space, the oil may enter the anterior chamber, causing corneal edema and, if in significant quantity, angle-obstruction glaucoma.
In phakic dogs, cataract formation has been associated with intravitreal SiO. Silicone oil is routinely left within the vitreous after retinal detachment surgery in dogs, and is not removed unless it escapes into the anterior chamber. In dogs, intravitreal silicone oil appears to be a reasonable vitreous substitute; in humans, silicone oil is usually removed 3—6 months post-surgery, and not left long term. Small animal patients, presented for possible vitreous aspiration, usually have exudative retinal detachments, intense chorioretinitis with vitreal infiltration, and endophthalmitis.
Often the ophthalmic disease is part of a systemic infectious disease, and the vitreal aspirate may assist in identification of the infectious agent. Systemic aspergillosis, blastomycosis, and cryptococcosis can often be diagnosed by vitreous aspiration and the demonstration of organisms within the aspirate.
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During vitreal aspirations, the hypodermic needle can often be directed under direct observation through a dilated pupil to the inflammatory material suspended within the vitreous. Hence, the diagnostic value of vitreal aspirates with a fairly clear anterior segment and lens is quite high. When the cornea, pupil or lens prevents direct observation of the hypodermic needle within the vitreous, the accuracy of the technique declines. Concurrent ultrasonography during vitreous aspiration in eyes with complete opacities can ensure that the hypodermic needle is positioned as accurately as possible within the vitreal body.
Small animal patients with vitreal diseases that may require partial-to-complete surgical excision are usually presented with lens displacement, with or without concurrent secondary and aqueous misdirection or malignant glaucoma, or postoperatively after cataract surgery. Formed or gel vitreous, partially herniated in the pupil and anterior chamber, appears as a formed, slightly translucent bulge with occasional fine white fibril strands. Corneal contact will cause focal edema.
The pupil margin can be distorted by formed vitreous, and vitreous strands may extend from the pupil into the previous corneal or limbal incision. If the pupil is miotic or miotics are inadvertently instilled, pupillary occlusion with the formed or gel vitreal herniation may result, necessitating additional therapy for the secondary glaucoma. Medical therapy is usually first attempted for vitreal herniations without corneal contact. Topical corticosteroids and mydriatics are used to suppress the iridocyclitis.
The resultant pupillary dilatation decreases the possibility of pupillary occlusion with the herniated vitreous and secondary glaucoma. Ideally, the herniated vitreous will retract behind the dilated pupil and remain. The effects of mannitol in a highly inflamed eye are usually less than optimal because the blood—aqueous barrier is reduced, and the osmotic imbalance caused by the intravascular mannitol is diminished. Surgical treatment of retinal detachment has been reported in dogs with serous retinal detachments secondary to optic disk pits or idiopathic Fig.http://argo-karaganda.kz/scripts/wulehoco/4207.php
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As indicated in an earlier section, exudative retinal detachments associated with posterior segment inflammations, systemic hypertension, and other causes are treated by therapy for the specific systemic disorder, and systemic corticosteroids and diuretics to attempt to remove the subretinal fluids before the retinal degeneration becomes advanced.
Unfortunately, most retinal detachments are presented late in small animals, and often entire retinas are detached in both eyes. Retinal detachments that develop after lens and cataract removal are often detected earlier during the periodic postoperative examinations Fig.
In this section, the fundamentals of vitreoretinal surgery are presented. As these types of surgical procedure are still evolving in the dog, and to a limited extent in cats, textbooks devoted to retinal detachment surgery in humans should be consulted for additional details.