Introduction
Wide-angle viewing systems are used for many intraocular procedures that involve vitrectomy and diagnostic inspection of the peripheral and posterior retina. A wide-angle system can be converted to a conventionally focused contact lens system when high magnification is required. Many complex surgeries, such as those with diabetic vitreous hemorrhages, tractional retinal detachments and proliferative vitreoretinopathy, can be more readily completed with the use of a wide-angle viewing system, particularly when there is significant pathology anterior to the equator. Panretinal endophotocoagulation, dissection of epiretinal and subretinal membranes, and gas-fluid exchange are all facilitated. The surgeon can concentrate on a focused area of the retina while still having a broad field of view. This is of particular importance during the peeling and dissection of membranes and the creation of a posterior vitreous detachment, as these maneuvers can exert significant and potentially dangerous, peripheral vitreoretinal traction that could lead to retinal breaks or detachment. These systems can be used with phakic, aphakic and pseudophakic patients and under various conditions, such as fluid, air, gas and silicone oil. The indirect systems can remain in focus with minimal adjustment when the index of refraction of the vitreous substitute is changed.
Wide-angle viewing systems offer a number of advantages over standard-view contact lens systems. They give a broader view of the pathology with better depth of field while displaying versatility, as they can be used with contact lenses, binocular indirect ophthalmoscopes, or no lenses at all. They provide the surgeon with a good surgical view under conditions other than fluid, such as with air, gas, or silicone oil. They also allow one to avoid the disadvantages seen with contact lens systems, such as corneal trauma, changes in intraocular pressure (IOP), poor view with lens or corneal opacities, or the need for multiple lenses. Disadvantages with wide-angle viewing systems include the need initially for more expensive equipment and the negotiation of a steeper learning curve in trying to obtain an optimally focused wide-field view. Contact lenses have traditionally been more readily available, less expensive, requiring of less maintenance, and not needing an associated re-inverting system.
Wide-angle viewing systems are either noncontact or contact in nature. Noncontact viewing systems are typically made of a series of lenses that are mechanically suspended above the surface of the eye. They allow the surgeon to manipulate the eye and still maintain good visualization while the eye is rotated during surgery. They provide good views in eyes with atypical corneal curvatures and opacities. The surgeon can operate without a skilled assistant as the lenses provide good depth of view in all fields of eye movement. They avoid the corneal trauma that can be seen with contact systems. Wide-field contact 4lens systems require a skilled assistant (for those that are hand held), can change IOP, do not allow much eye movement (as the image can be lost or distorted when the eye is rotated or the optical center of the lens is not matched with the moving eye), and can be difficult to use in eyes with corneal abnormalities. On the other hand, the wide-field contact lens systems can provide up to 150° field of view and do not have the disadvantages associated with noncontact systems, such as the learning curve needed to obtain and maintain focus, cost, adaptability to microscopes, and reduced optical resolution.1
Overview of Available Systems
Visualization of the posterior segment during vitreoretinal surgery can be accomplished via various contact and noncontact methods. Hand-held, plano-concave contact lenses neutralize the high convergence effect of the corneal curvature, which thereby permits the operating microscope to focus on the central vitreous and posterior retina with an approximately 20° view. For work on the equatorial retina, the surgeon may tilt this flat contact lens for a fairly highly magnified view, albeit with some slight aberration. Lenses may be used with sew-on retaining rings that stabilize them without an assistant; however, a series of special prismatic lenses may be required to view the periphery.1 A biconcave lens increases the visual field to 35°. The Landers biconcave lens (Ocular Instruments, Bellevue, WA, USA) allows visualization of the fundus beyond the equator in gas-filled pseudophakic and phakic eyes.
All wide-angle systems generate an inverted fundus view and thus require a device to convert the image to a normal orientation for the surgeon. Indirect ophthalmoscopic viewing lenses, such as the Pan Funduscope (Rodenstock, Munich, Germany), were developed for panretinal photocoagulation and allow a wider, though inverted, view through the pupil. Such an inverted view is difficult and impractical for surgical viewing. The stereoscopic digital inverter (SDI, InterMed Sales Corporation, Miami, Florida, USA) is one of a class of devices that were developed to re-invert the image for use with wide-field lenses.2 Currently available wide-angle viewing systems include:
- The Volk re-inverting operating lens system (ROLS) [Volk miniature indirect contact lenses with both standard lenses and self-stabilizing lenses] (Volk Optical, Inc., Mentor, OH, USA).
- The AVI inverter (Avi Greenblatt, New York, New York, USA) with miniature indirect contact lenses.
- The Iris Medical contact wide-angle system (Iris Medical Instruments, Mountain View, CA, USA).
- The BIOM (Binocular Indirect Ophthalmoscope)/SDI (Stereoscopic Diagonal Inverter) noncontact system with or without a miniature, indirect viewing contact lens3 (Oculus, Inc., Lynnwood, WA, USA).
- The EIBOS (Erected Image Binocular Ophthalmoscope) noncontact system (Möller-Wedel International GmbH, Wedel, Germany).
The SDI (Fig. 1.1) can be used with noncontact and contact lens because it is mounted in the stack of the scope. Other systems incorporate the ROLS or AVI image inverter with miniature indirect wide-angle contact lenses. The SDI can be changed automatically from an inverted image to non-inverted image with a foot pedal or assistant, where the ROLS and AVI require manual engagement. It is possible to use any inverter system with any objective lens.
The ROLS inverter by Volk uses a single-element image-erecting prism with four optical surfaces that are shared by the right and left eye systems. It is offered in a “Zeiss style”, fitting Zeiss, Topcon, Moeller and Inam scopes that accept Zeiss accessories and a “Wild style”, which fits only the Leica or Wild microscopes. A diode laser safety filter is built into the inverter (Fig. 1.1). The ROLS does not contact the eye 5and needs no sterilization. The AVI system sits in the stack of the microscope, is relatively compact (less than 1.5 inches thick and approximately one pound in weight), and is compatible with Wild, Zeiss and Moeller scopes. With the miniature indirect contact lens, the AVI system can offer 130° of peripheral viewing.
Comparison of Contact Lens Systems
Two traditionally used wide-angle contact lens systems include a floating plano-concave lens, supported by a sutured lens ring and a plano-concave irrigating hand-held contact lens.4,5 A contact lens with one suture has also been described.6 Sutureless and self-stabilizing lenses are attractive options for wide-angle viewing. Chalam et al.7 described a standard 60-D plano-concave lens with the radius of curvature of 6.7 mm (less than the corneal curvature) modified with the addition of four footplates that facilitate lens stability and centration without the aid of an assistant. Viscoelastic material is placed between the lens and cornea, creating negative suction which keeps the lens firmly in place on the cornea. This lens allows one to circumvent one drawback of the sew-on lens ring, which is the potential bleeding from the suture placement that can track under the lens and then obscure the surgeon's view. Ikuno et al.8 have recently introduced a sutureless contact lens system in which the lens is affixed with silicone bands. This system improves upon many of the drawbacks mentioned above, though rotation of globe is difficult due to the restriction caused by the silicone bands.
The MiniQuad lens (Volk Optical, Inc., Mentor, OH, USA) is a modified self-stabilizing contact lens. The posterior contact surface of the lens is extended with four footplates. The static field of view of the lens is 106°, while the dynamic view increases its field to 127°. The surgeon has unobstructed entry of the instruments through the sclerotomies. Scleral indentation, if required, can be done without interference of the footplates. Unfortunately, the lens may not be completely self-retaining in all situations and centration may require minimal assistance in some instances.9
Nakata et al.10 have described features of the ClariVIT contact lens made of glass and polymethyl methacrylate without a plastic rim (Volk Optical, Inc., Mentor, OH, USA). The diameter is reduced to 16.2 mm (compared to the 18 mm diameter of the MiniQuad). A smaller diameter helps eliminate contact between surgical instruments and the wide-angle lens. The optical properties are otherwise identical to the standard wide-angle lens. Its field of view (127°) is the same as the MiniQuad and it allows for a good view through a small pupil even when the vitreous cavity is filled with gas.
The Volk wide-angle contact lenses can be sterilized with ethylene oxide gas at 130° F or disinfected with Sterrad, Steris, or glutaraldehyde. Sterilization of other contact lenses is traditionally done either by ethylene oxide gas or chemically by glutaraldehyde 2% or povidone iodine 5%. Sterilization via autoclaving is cost effective, fast and widely used. Unfortunately, autoclaving can irreparably damage most lenses. Shah et al.11 described a wide-angle contact lens, which has two lens pieces contained together within a high temperature-resistant (150°C) plastic casing. The inferior lens has footplates and is made of acrylic and the superior lens is made of glass. This self-stabilizing wide-angle contact lens can be sterilized via autoclaving and is thus less costly and needs reduced time for sterilization. The field of view is 106° in the static view and 127° in the dynamic view. After use, its parts are detached, cleaned, put in a lens case and wrapped. The flash autoclave allows for immediate use when needed.
Comparison of Noncontact Wide-angle Systems
The BIOM (Fig. 1.2) is a noncontact device used for vitreous surgery under the operating microscope. It provides a field of view of typically up to 120°, and a dynamic view of up to 135°. It is adaptable to many microscopes and can be used with multiple wide-angle contact lenses. Its versatility allows it to be flipped in and out of use during surgery (Figs 1.3A and B). It is readily adaptable for use with various lighting systems, such as the bullet light pipe and peripheral chandelier devices, which produce wide-angle illumination that enhances the surgeon's view and allows for bimanual surgical techniques.
There are 2 models of the BIOM: A closed cone device and an open arm device that extends from a dove-tailed plate screwed onto the bottom of a microscope. There is a condensing lens on the top of the small indirect viewing tower on both models, as well as a smaller objective lens that is combined with the SDI in the stack on the microscope. The surgeon simply moves the indirect viewing tower in or out from under the microscope lens system to switch between the BIOM wide-angle intraocular system and regular viewing.
Figure 1.2: BIOM. The BIOM, in addition to the plate used to anchor it onto the scope, also has a knurled knob for focusing, which may be adjusted via an assistant or automated pedal. The reduction lens and wide-angle lens come in disposable and nondisposable forms
Figures 1.3A and B: BIOM in different positions. (A) The BIOM is flipped up, allowing the use of the microscope with other lenses; (B) The BIOM and wide-angle lens are engaged
The surgeon then inverts the image by either using a foot pedal or assistant to activate the inverter. Gross focus is obtained by manipulating the microscope focus while fine focus is obtained by adjusting the knurled knob on the BIOM device (turning it counterclockwise allows the objective lens to elevate and focus down).
Sterilization can be accomplished via gas or autoclave. The lenses can be either sterilized with ethylene oxide or alkaline glutaraldehyde solution (e.g. Cidex). The SDI is incorporated into the scope and is not sterile. It has an internalized prismatic system with near-zero light escape to achieve maximal illumination and light intensity. The SDI inverts the indirect image from the BIOM to a conventional upright image. The interaction between the surgical scope and BIOM has the following variables, all of which can be manipulated to vary the image for the surgeon:
- Power of the BIOM objective lens
- Distance of the BIOM wide-field lens from the scope
- Distance of the BIOM wide-field lens from the cornea.
The EIBOS noncontact lens system is similar to the combined BIOM/SDI system in function but has a one-piece design with the lenses and inverter housed in a single unit (Figs 1.4A and B). It thus cannot be used with varying wide-angle contact lenses. This one-piece design does not allow sterilization of the entire unit, so it must be draped with a sterile covering. The objective lens itself can be sterilized to prevent contamination of the surgical field. The entire unit is spring balanced as a safety feature so the objective lens does not contact the eye.
Figures 1.4A and B: EIBOS. (A) The entire EIBOS unit is spring balanced and allows for a shorter microscope stack; (B) The EIBOS is a one-piece design with the lenses and inverter housed in a single unit
Focusing is done with a mounted sterile lever, which changes the internal lens distances without changing the distance of the lens from the patient's eye. The retinal image appears in the conventional orientation without the surgeon having to specifically manipulate an inverter. This combined system allows for a shorter scope stack, which thereby leads to better ergonomic management of the surgical field such as with the introduction and removal of instrumentation and devices around the eye.
Adjuncts to Viewing
Intermittent corneal wetting with balanced salt solution (BSS), viscoelastic, or hydroxypropyl methylcellulose solution diluted with BSS is required with noncontact viewing systems to maintain corneal clarity. Good endoillumination enhances the performance of wide-angle viewing systems, whether provided by a conventional light pipe, wide-angle endoilluminator, lighted instruments, single or multiport chandelier illumination systems, or a chandelier lighted infusion system. The microscope light is turned off when endoillumination is used. Slightly tilting the globe and using endoillumination in both a diffuse and tangential orientation maximizes the surgeon's view of the periphery. Magnification is achieved and manipulated by using the zoom function of the microscope and/or by lowering the microscope so the objective lens is closer to cornea. Having a clear visual axis with as large of a pupil as possible certainly enhances posterior segment visualization. Ideally, a pupil larger than 2.5 mm offers a near full view of the fundus. Iris hooks can enlarge the pupil but lensectomy, synechiolysis, penetrating keratoplasty, or keratoprosthesis may at times be needed to clear the visual axis.
Wide-angle viewing systems are used for many intraocular procedures and for effective inspection of the peripheral retina. They can be used with phakic, aphakic and pseudophakic eyes as well as under various viewing conditions in eyes filled with gas, fluid, or silicone oil. They offer a broad view of the patient's pathology while providing good depth perception. Both contact and noncontact systems are available. For contact lenses, there are suture and sutureless lenses available with dynamic views of 150°. Noncontact systems provide 135° of view but avoid several disadvantages of contact lens systems. Proper case selection and use of illumination and magnification are adjunctive maneuvers that aid in viewing with these systems and are as vital to obtaining an ideal surgical view as the specific wide-angle viewing system that is selected.
References
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- Spitznas M. A binocular indirect ophthalmoscope (BIOM) for wide-angle vitreous surgery. Graefes Ach Clin Exp Ophthalmol. 1987; 225: 13–5.
- Tolentino FI, Freeman HM. A new lens for closed pars plana vitrectomy. Arch Ophthalmol. 1979; 97: 2197–8.
- Parel JM, Machemer R. Steam-sterilizable fundus contact lenses. Arch Ophthalmol. 1981; 99: 151.
- Lewis JM, Ohji M, Tano Y. A technique for contact lens fixation during vitreous surgery. Ophthalmic Surg Lasers. 1996; 27: 891–3.
- Chalam KV, Patel CC, Shah VA. Newly designed self-retaining contact lens for vitreous surgery. Am J Ophthalmol. 2003; 135: 544–6.
- Ikuno Y, Ohji M, Kusaka S, et al. Sutureless contact lens ring system during vitrectomy. Am J Ophthalmol. 2002; 133: 847–8.
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- Nakata K, Ohji M, Ikuno Y, et al. Wide-angle viewing lens for vitrectomy. Am J Ophthalmol. 2004; 137: 760–2.
- Shah VA, Chalam KV. Autoclavable wide-angle contact lens for vitreous surgery. Am J Ophthalmol. 2004; 137: 359–60.