Management of Hazy View And Small Pupil During Vitreoretinal Surgery
Problems with visualization can add an additional challenge to retinal surgery.
JAY CHHABLANI, MD · TANDAVA KRISHNAN, MD · SRIPATHI KAMATH, MD
Visualization of the surgical field is crucial in any ophthalmic surgery, especially in vitreoretinal surgery. The difference in the refractive indices of the various transparent structures of the eye — the cornea, aqueous humor, crystalline lens, and vitreous humor — and the relatively small size of the eye require special optical systems, such as operating microscopes, and an array of contact or noncontact lenses. In addition, special maneuvers are often necessary to achieve adequate visibility intraoperatively.
Recently available visualization systems have considerably improved visibility during vitreoretinal surgery. However, various challenges still exist, increasing surgical duration and the chances of complications. In this article, we describe various causes of hazy media and small pupil during vitreoretinal surgery and their management.
PREOPERATIVE CAUSES OF HAZY MEDIA
Various preoperative factors can impede visibility intraoperatively.1,2 Assessment of the eye to identify these preoperative factors can ensure the surgeon is better prepared to address them.
Surgeons can preoperatively address several corneal factors that can impact visibility. For instance, we can treat corneal edema preoperatively with topical steroids and glycerin.
Jay Chhablani, MD is on the faculty of the L. V. Prasad Eye Institute in Hyderabad, India. Tandava Krishnan, MD, is on the faculty of the Pushpagiri Eye Institute in Secunderabad, India. Sripathi Kamath, MD is a vitreoretina fellow at L. V. Prasad Eye Institute in Hyderabad, India. None of the authors reports any financial interests in any the products mentioned in this article. Dr. Chhablani can be reached via e-mail at firstname.lastname@example.org.
In addition, the presence of corneal scars may alter the surgical plan, depending upon the location and degree of opacification. The surgeon should plan optical iridectomy or penetrating keratoplasty or use a temporary keratoprosthesis. The presence of corneal sutures in the visual axis can be troublesome during surgery. As a result, preoperative planning for suture removal can be beneficial.
Before vitreoretinal surgery, the surgeon should address the presence of pannus or a pterygium obstructing the visual axis. He or she should also perform a careful examination of the cornea to identify blood staining, especially in cases of trauma or hyphema. In cases of severe staining, penetrating keratoplasty is an option.
In cases of band-shaped keratopathy, ethylenediaminetetraacetic acid chelation (0.05 mM, 1.5%) is usually effective in early cases. However, if the kreatopathy is recurrent or refractory, the surgeon can plan phototherapeutic keratectomy.
History of Refractive Surgery
A history of refractive surgery warrants a careful preoperative examination for a thin LASIK flap. Incidental separation of the LASIK flap during epithelial removal has been reported in vitreoretinal surgery.3
The presence of radial keratotomy (RK) scars during surgery can be very disturbing because of the glare they cause. RK scars are an indicator of high myopia and require careful examination of the sclera.
Dropped nucleus after complicated cataract surgery is a common referral for vitreoretinal surgeons. Before planning the vitreous surgery, the surgeon should manage the presence of a significant Descemet’s membrane detachment.
Figure 1. Brown discoloration of a multipiece multifocal hydrophobic acrylic posterior chamber IOL.
COURTESY: MICHAEL P. KELLY, CPT, CHI, AND MEMBERS OF DUKE EYE IMAGING TEAM
The presence of vitreous strands in the anterior chamber in pseudophakic patients can cause cystoid macular edema. Also, before planning vitreoretinal surgery, the surgeon should identify posterior capsular opacification and plan preoperative YAG capsulotomy or intraoperative membranectomy accordingly.
The surgeon should carefully consider the decision to inject oil while creating an opening in the posterior capsule. This injection will prevent the entry of oil into the anterior chamber.
Significant tilt or subluxation of an IOL requires its removal. Patients should be counseled preoperatively of the potential for aphakia management after surgery. In cases of pigment dusting on the IOL, the surgeon can remove most pigments during surgery with a jet of fluid or by rubbing the IOL with a soft-tip cannula. However, significant pigment may demand removal of the IOL.
Newer multifocal IOLs can also be troublesome due to diffraction at difference zones (Figure 1). Most vitreoretinal surgeries are possible with these IOLs, although sometimes removal is necessary.4
INTRAOPERATIVE CAUSES OF HAZY MEDIA
Among the several intraoperative causes of poor visibility,5 noncontact visualization lens fogging can arise as the result of condensation on the lens surface.
For instance, if the drape does not properly adhere to the skin around the nose, fogging may occur due to the patient’s exhaled air escaping. Careful draping preoperatively can prevent this. Keeping a wet cotton bud just at the medial end of the opening in the drape can also help. In some cases, the drapes may need to be replaced.
Frequent application of topical anesthetics and povidone-iodine can cause corneal haze. Inadvertent epithelial defects can occur during draping or encirclage, also resulting in haze.
Improper corneal irrigation can result in corneal surface drying, causing cornea to lose its transparent nature. Use of an improper coupling agent and the subsequent rise in IOP can also cause corneal haze.
Prolonged surgery, especially in diabetics who have poor corneal epithelial function, can result in epithelial edema. When using a contact lens, avoiding excessive pressure and reducing the infusion pressure can help prevent corneal edema.
Regular irrigation of the cornea with balanced salt solution or a viscoelastic agent also helps maintain corneal transparency. The surgeon can initially attempt removal of edematous epithelium with a dry/wet cotton tip applicator. If this does not work, epithelial debridement with a broad blade, leaving behind the peripheral (at least 2 mm) rim near the limbus, can sometimes restore clarity.
However, once the epithelium is debrided, the cornea becomes dry very fast. Application of viscoelastic can help retain moisture.
Fluctuation of anterior-chamber depth during surgery can result in bleeding from the angles. This risk is especially high in eyes with previous attacks of uveitis, resulting in blood in the anterior chamber.
In such cases, the surgeon should take care to maintain the anterior-chamber depth and IOP. In the presence of hyphema, the surgeon can attempt anterior-chamber irrigation with balanced salt solution. He or she should follow this irrigation with an injection of viscoelastic substance into the anterior chamber, to restore clarity.
During vitreous surgery, pigment release into the anterior chamber can occur due to excessive manipulation, especially in pseudophakic eyes. As a result, minimal maneuvering in the anterior segment is advisable.
Injection of viscoelastic material in the anterior chamber can provide a clear view for a short duration. We suggest rapid completion of surgery at this stage. Otherwise, anterior-chamber irrigation with BSS is mandatory.
Air in the anterior chamber can occur in cases of posterior capsule dehiscence or loss of zonular integrity. During fluid-air exchange, air can enter the anterior chamber and impair visibility.
To restore visibility, the surgeon can fill the anterior chamber completely with air to create a single medium, or with viscoelastic substance and an additional layer of coating on the posterior lens surface.
Condensation on IOLs occurs mostly after fluid-air exchange. The likelihood of condensation is similar with acrylic or PMMA IOLs. Preservation of anterior vitreous can prevent this complication.
Use of perfluorocarbon liquids also prevents IOL fogging. The surgeon can clear the back surface of the IOL with a flute needle and coat viscoelastic substance on the posterior surface of the IOL.
Cataract formation can occur during prolonged surgeries. If noted preoperatively, it is better to perform cataract surgery before vitreoretinal surgery, either during the same sitting or in a staged manner.
The surgeon can manage minor lens touch without cataract extraction and plan cataract surgery with an IOL later. However, if the cataract becomes significant intraoperatively, and the posterior segment fills with fluid, the surgeon can perform cataract surgery during vitreoretinal surgery.
SURGICAL OPTIONS FOR HAZY MEDIA
Several options exist for the management of corneal haze along with vitreoretinal surgery.2 The options include vitrectomy with temporary keratoprosthesis and vitrectomy with endoscopy. The advantages that these techniques offer over open sky techniques include lower risks of intraocular hemorrhage and tissue prolapse, as well as greater possibility of globe manipulation.
Landers introduced a temporary keratoprosthesis made of PMMA cylinder in 1981.2 It is a minus-powered lens enabling posterior-segment surgery without the use of an additional lens. However, visualization of the periphery is limited and requires indentation. A prismatic effect due to the cylinder is another limitation.
Eckardt introduced a temporary silicone keratoprosthesis in 1987. It provides greater access to the periphery due to its shorter shaft length. The surgical procedure is subject to the availability of corneal tissue for grafting, and it requires an additional lens.
The advantages of combining penetrating keratoplasty with retinal surgery include a wider, three-dimensional field of view, whereas the disadvantages include a greater likelihood of graft failure if the combined procedure is performed within two months after trauma. Additional procedures, such as silicone oil injections, can result in further stress on the donor endothelium, which can result in graft failure.
Figure 2. Management of small pupil. (OVDs = ophthalmic viscosurgical devices.)
Endoscopic Viewing Systems
Surgeons can perform endoscopic viewing system–assisted vitrectomy in settings where corneal tissue is not readily available.6 It provides 360º of high magnification viewing, up to the anterior zonule vitreous base. The surgical procedure takes less time than keratoprosthesis once the surgeon is conversant with the technique. He or she can easily manage cyclitic membranes and anterior proliferative vitreoretinopathy.
The surgeon should take care to introduce the system into the eye carefully, to avoid inadvertent formation of a false track subretinally or in the suprachoroidal space. The surgeon must also deal with changes in intraocular perspective in eyes with trauma due to vitreous hemorrhage and globe distortion.
The disadvantages2,6 of endoscopic viewing systems include:
• absence of stereopsis;
• inability to perform bimanual surgeries;
• limited field of view;
• low video image quality;
• high costs of endoscopy systems; and
• a steep learning curve.
The presence of a small pupil can compromise visibility. Small pupil can be caused by pseudoexfoliation, posterior synechiae, surgery, and trauma. It can also be drug-induced. To enable proper surgical planning, the preoperative evaluation must assess for the extent of pupillary dilatation.
We can divide the various aids, which help in improving visualization, into aids that help to increase the field of view and those that increase pupil size (Figure 2, page 43). Wide-angle viewing systems belong to the former category; they provide an increased field of vision irrespective of pupil size.7
Increasing Pupil Size
Agents that increase pupil size are pharmacological and mechanical in nature. While no drug has received FDA approval for the prevention of intraoperative miosis in vitreoretinal surgery, topical 0.1% diclofenac has had good intraoperative mydriatic effects.8
Intracameral application of epinephrine (1:4,000) or norepinephrine (1:200) can also result in pupillary dilatation. However, the surgeon should take care in patients with hypertension and cardiac ailments.
Surgeons commonly use iris retractors and pupil expansion rings to stretch the pupil mechanically and increase its size. Kuglen iris hooks are currently the most commonly used iris retractors in posterior-segment surgeries.
These hooks are made of 5-0 nylon, and the surgeon introduces them into the eye just posterior to the limbus, in approximately four sites on a plane parallel to the iris. The surgeon must place them symmetrically to avoid unnecessary pupillary stretching.
Improper placement or removal of the hooks can result in iris prolapse, irregular postoperative pupillary function, and Descemet’s membrane detachment.9 However, due to limitation of the working space, performing a surgery using a contact lens can become ungainly at times.
In cases in which intraoperative miosis is likely, the use of highly cohesive ophthalmic viscoelastic devices (OVDs), such as the Healon 5 with or without Viscoat (Abbott Medical Optics, Inc., Santa Ana, CA), is advisable. These devices are especially useful in cases with combined cataract and retinal surgeries.10
In eyes with localized synechiae, using an iris spatula in the presence of an OVD to break posterior synechiae can facilitate pupillary dilatation. In addition, mechanical pupillary stretching can temporarily help to expand pupillary size, but it does not prevent progressive miosis.9 The surgeon can also perform sphincterectomy or sector iridectomy.
In the presence of intraoperative media haze, meticulous evaluation for the cause of haze and patient management of the same can result in better surgical outcomes. Small pupil can be managed with medication or mechanical devices. Proper preoperative assessment of the eye, for the possible causes of poor visualization and of small pupil, can help in better planning of surgery. RP
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