Vitrectomy pars plana

Pars plana vitrectomy is a microsurgical procedure that removes the vitreous to provide better access to the damaged retina. It is most often performed through three separate openings in the pars plana.

Goals of vitrectomy

• Excision of the posterior hyaloid membrane to the posterior border of the vitreous base in eyes with retinal detachment is the most important task. The so-called "main" vitrectomy, in which the PHM and associated retinal membranes remain intact, is justified only in cases of endophthalmitis.
• Relief of vitreoretinal traction by dissection of the vitreoretinal membrane and/or retinotomy.
• Retinal manipulation and adhesion.
• Creation of space inside the vitrified cavity for subsequent internal tamponade.
• Various purposes (depending on the case): removal of opacified vitreous, cataracts, dislocated lens fragments or intraocular foreign bodies.

Indications for vitrectomy

Rhegmatogenous retinal detachment

Uncomplicated retinal detachments: Although scleral buckling is usually effective, primary vitrectomy is used more often because it has the following advantages:

• Fewer manipulations, since sometimes it is not necessary to perform scleral indentation.
• Cryo- or laser coagulation can be performed after the retina has been reattached, which reduces the impact of destructive energy.
• Tamponade with one or another agent ensures postoperative blocking of the retinal tear from the inside.

Complicated retinal detachments, in which retinal tears cannot be closed by simple scleral indentation due to their large size, when localized in the posterior pole and in combination with PVR.

Traction retinal detachment

In proliferative diabetic retinopathy, vitrectomy is indicated if the retinal detachment involves the macula or poses a threat to it; it can be combined with internal panretinal laser coagulation. Combined traction-rhegmatogenous retinal detachment should be operated on immediately, even if the macula is not involved, since very rapid leakage of subretinal fluid involving the macula is possible.

In penetrating injuries, vitrectomy is aimed at visual rehabilitation and reducing traction that predisposes to retinal detachment.

Preparation

• the infusion cannula is placed into the inferotemporal sclerotomy opening at a distance of 3.5 mm from the limbus;
• 2 additional sclerotomy holes are made corresponding to the 10 and 2 o'clock meridians, through which the vitreotome and fiber-optic tip are inserted;
• The posterior hyaline membrane and the vitreous body in the center are removed.

Dissection of the membranes of local retinal folds is as follows:

• the end of the vertical cutting scissors is inserted into the membrane between two adjacent retinal folds, and the membrane is pulled towards the "serrated" line until it is torn away from the retinal surface;
• perform internal fluid-air exchange with subsequent retinopexy of retinal breaks;
• the base of the vitreous body is supported by a wide scleral buckle;

Auxiliary retinotomy may be required after membrane dissection if retinal mobility is considered insufficient for reattachment.

Excision of subretinal membranes may be necessary in certain cases.

Tools

The instruments are presented in a kit; in addition to the vitreotome, a number of other instruments are required. The diameter of the axis of most instruments is the same size, which allows them to be interchangeable and inserted through the sclerotomy opening,

• The vitreotome has an internal guillotine blade that vibrates at 800 times/minute.
• Intraocular illumination is provided by a fiber optic tip.
• Infusion cannula.
• Additional instruments include scissors and tweezers, an outflow needle, an endolaser, and an indirect ophthalmoscope.

Tamponade substances

The ideal substance should have high surface tension, be optically transparent and biologically inert. In the absence of such an ideal substance, the following substances are currently used.

Air is the most commonly used and is usually adequate in uncomplicated cases. It is more readily available but must be filtered to remove microorganisms. Its main disadvantage is its rapid resorption: a 2 ml bubble is resorbed within 3 days, whereas chorioretinal fusion induced by laser or cryocoagulation takes about 10 days.

Expanding gases are preferred in complicated cases requiring prolonged intraocular tamponade. The duration of bubble retention in the eye depends on the concentration of the gas and the volume injected. For example:

• Stabilization of the posterior retina during epiretinal membrane dissection in eyes with PVR.
• Straightening of a giant retinal tear.
• Posterior displacement of dislocated fragments of the lens or IOL.

Silicone oil has low gravity and can float. It allows for more controlled surgical manipulations and can be used for prolonged postoperative intraocular tamponade.

Technique

Proliferative vitreoretinopathy. The aim of the operation is to remove transvitreal traction by vitrectomy, superficial traction by dissection of membranes, which will ensure the mobility of the retina and subsequent closure of the breaks,

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Postoperative complications of vitrectomy

Increased intraocular pressure may be caused by the following reasons.

• Excessive volume of gas introduced
• Early glaucoma induced by silicone oil accumulation in the anterior chamber.
• Late glaucoma induced by possible block of the trabecular apparatus due to silicone oil in the anterior chamber. This can be avoided if the silicone oil is removed in time either through the pars plana in phakic eyes or through the limbus in aphakmic eyes.
• Shadow cells or steroid glaucoma.

Cataracts can be caused by:

• Use of gas. Usually transient and controlled by using low concentrations and small volumes of gas,
• Using silicone oil. Develops in almost all cases. In this case, removal of silicone oil is indicated in combination with cataract extraction.
• Late compaction of the nucleus, which sometimes develops over the course of 5-10 years.

Recurrent retinal detachment most often occurs after gas absorption (3-6 weeks after surgery) or after removal of silicone oil. The main causes are:

• Recurrence of an old tear due to inadequate surgical dissection in eyes with PVR or re-proliferation of epiretinal membranes is most common in PDR.
• New or missed breaks, especially around sclerotomy holes for pars plana vitrectomy,

Early removal of silicone oil is associated with a 25% risk of recurrent retinal detachment in eyes with PVR and giant tears and an 11% risk in eyes with PDR.