Chapter 12 Vitreoretinal surgery
Types of retinal detachment 360
Types of vitreoretinal surgery 360
Clinical evaluation of retinal detachments 360
Instrumentation for vitreoretinal surgeries 361
Preoperative considerations for vitreal aspiration and removal 362
Preoperative considerations for retinal detachments 363
TYPES OF VITREORETINAL SURGERY 363
Adaptations for large animals and special species 369
Suprachoroidal cyclosporine implants for the treatment of equine recurrent uveitis 369
Pars plana (anterior) vitrectomy 370
Surgical pathophysiology
Clinical evaluation of retinal detachments
Box 12.1 General principles for the treatment of rhegmatogenous retinal detachments
Part A Principles
1. Closure of retinal break: By diathermy, cryotherapy, or laser.
2. Collapse of the space between the separated retinal layers:
3. Excision of vitreal and/or inflammatory traction bands that appear to pull on the retina.
4. Occasional temporary intravitreal injections of silicone oil and/or perfluorocarbon gases to push and flatten (tamponade) the area of retinal detachment.
5. 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.
Part B Specialized instruments for pars plana retinal detachment surgery
20 g microvitreoretinal (MVR) blades
20 g end gripping microforceps
20 g DeJuan intraocular forceps
20 g horizontal and vertical forceps
Modified from Smith PJ 1999 Surgery of the canine posterior segment. In: Gelatt KN (ed.) Veterinary Ophthalmology, 3rd edn. Lippincott, Williams and Wilkins, Baltimore, p 935–980.
Instrumentation for vitreoretinal surgeries
Preoperative considerations for retinal detachments
Surgical treatment of retinal detachment has been reported in dogs with serous retinal detachments secondary to optic disk pits or idiopathic (Fig. 12.6), and for rhegmatogenous retinal detachments associated with retinal holes or tears that developed after cataract surgery. 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. 12.7).
Surgery of the vitreous
Hyalocentesis/vitreous paracentesis
Vitreous aspiration procedure
Hyalocentesis is performed after the onset of general anesthesia, clipping of the eyelid hair, and cleansing of the eyelid skin, conjunctival and corneal surfaces with 0.5% povidone–iodine solution. The pupil is dilated before the onset of general anesthesia. For convenience, the eyelids are retracted by speculum. The pupil and anterior vitreous are usually visible. The bulbar conjunctiva is grasped by thumb forceps with teeth several millimeters posterior to the dorsal limbus (Fig. 12.9a). By calipers the site to penetrate the bulbar conjunctiva is determined as 6–9 mm (dorsal) to 8–9 mm (lateral) posterior to the limbus. At this position, the 22–23 g hypodermic needle, aimed at the optic disk, should penetrate the sclera and pars plana ciliaris to enter the anterior vitreous (Fig. 12.9b).
Intravitreal injections
Table 12.1 Doses for intravitreal antibiotics in the dog
Antibiotic | Dose |
---|---|
Amikacin | 0.4 mg |
Ampicillin | 5.0 mg |
Cefazolin | 2.25 mg |
Cephaloridine | 0.25 mg |
Chloramphenicol | 2.0 mg |
Gentamicin | 0.4 mg |
Tobramycin | 0.4 mg |
Vancomycin | 1.0 mg |
Transpupillary vitreal aspirations
The anterior chamber is maintained with viscoelastic agents.
The formed vitreous may be indistinguishable from the aqueous humor or liquefied vitreous, unless some vitreal floaters (cells, fibrils, opacities) are present (Fig. 12.10a). A blunt 18–20 g hypodermic needle, attached to a 1–3 mL syringe, is carefully inserted through the pupil and the remaining posterior lens capsule and/or anterior hyaloid face about 5 mm into the most dorsal vitreal space. Insertion of the hypodermic needle through the external sclera and pars plana ciliaris, as used for hyalocentesis, is not recommended as it may collapse the globe and cause additional formed vitreous to appear in the pupil (Fig. 12.10b). Liquid vitreous is always above the formed or gel portion, and shifts to remain dorsal during the different positions of the eye. As a result, the hypodermic needle to aspirate liquid vitreous must be placed in the upper vitreal body. Liquefied vitreous is slowly aspirated, usually 0.1–0.5 mL. Often with removal of the liquid vitreous, the formed vitreous within the pupil and anterior chamber will partially or completely shift behind the pupil.
The iridal diaphragm may appear somewhat concave after successful vitreous aspiration, and restoration of all formed vitreous to behind the pupil (Fig. 12.10c). As the gel vitreous and solutions used to lavage the anterior chamber are indistinguishable, a small air bubble may be injected into the anterior chamber to assist in detection of any residual gel vitreous (Fig. 12.10d). The air bubble should be freely maneuverable through the entire anterior chamber when all gel vitreous has been removed or retracted through the pupil. If some gel vitreous remains within the anterior chamber, the air bubble movement is restricted and may outline the formed vitreous. No formed or gel vitreous should remain in the anterior chamber at the conclusion of this technique.
Anterior/partial vitrectomy in small animals
When the anterior vitrectomy is performed immediately after lens or cataract removal, the majority of the procedure is performed within the anterior chamber. The formed vitreous may be clear or contain suspended cells, fibrin, vitreous opacities (such as with hyalosis), and blood. In the anterior vitrectomy procedure for anterior chamber vitreal presentation, small cellulose surgical sponges are touched to the formed vitreous (Fig. 12.11a).The adherent gel vitreous is slowly retracted and carefully cut with sharp iris or vitreous scissors. The scissors are held parallel to the surface of the iris to minimize traction on the deeper vitreous and indirectly on the retina (Fig. 12.11b). All gel vitreous within the anterior chamber may be removed by this procedure. The iris surface should be slightly concave afterwards because of the loss of formed vitreous immediately posterior to it (Fig. 12.11c). Many phacoemulsification units also offer vitrectomy capacity that can be used to cut and aspirate the formed vitreous from the anterior chamber.
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