Ординатура / Офтальмология / Английские материалы / Retinal and Vitreoretinal Diseases and Surgery_Boyd, Cortez, Sabates_2010

Wide-angleviewingsystemsareveryimpor- tant in vitreortinal surgery. The use of these systems enables simultaneous observation of a wide area of an ocular fundus, thereby making it possible to accurately view a vitreoretinal state during surgery. Therefore, save and comfortable surgery is possible by making good use of this system. In this chapter, we describe mainly how to use wide-angle viewing and its merits.

Introduction

In vitreoretinal surgery, it is extremely important to be able to see well an ocular fundus during surgery, and consequently a variety of surgical devices and lenses for observation of the fundus have been developed.

Lenses that have been used frequently in methods of observing the fundus since

the early years of vitreoretinal surgery are plano-concave lenses having a planar upper surface and a concave lower surface corresponding to the corneal radius of curvature. Plano-concave lenses provide a sharp observed image, and the magnification percentage is high. However, the visual field of observation is narrow, and only the central part of the fundus can be observed; as result, the upper surface is used as prism to observe the peripheral part of the fundus.

In addition, lenses such as a magnifying lens whose upper surface is convex to magnify and observe the central part of the fundus and a lens with both surfaces concave for fluidair exchange should be replaced frequently during operation. Further, in cases of small pupils or corneal opacity, the observation of the fundus is difficult.

With wide-angle viewing systems described in this chapter, a wide range

of the ocular fundus can be viewed during surgery. It is possible to view an entire image of the fundus whose state changes from moment to moment during surgery, thereby enabling safe and comfortable surgery.

In addition, a wide visual field can be achieved even for small pupils, and it is not necessary to replace lenses at the time of fluid-airexchangeandair-siliconeoilexchange. In addition, laser photocoagulation in the extreme peripheral region can be performed under scleral compression.

Types and Outline of Wide-

Angle Viewing Systems

As wide-angle viewing systems, there are contact lens-type (contact-type) used by being placed on the cornea and non-contact type for observation with the convex lens kept at a position 5-10 mm away from the cornea.

Contact Lens-Type (Contact-Type)

This type is used by being placed on the cornea with the use of a lens ring sewed on the corneal limbus. There are various kinds.1,2,3 We mention currently typical products: Mini Quad and ClariVIT.

With Mini Quad (Mini Quad SSV ACS; Volk Optical Inc., Mentor, OH, USA) (Figure 1), the ocular fundus can be observed up to 127°. The observation is possible up to the ora serrata, and fluid-air exchange is also possible without replacing lenses. Under air perfusion, the observation is possible up to the pars-plana. ClariVIT (ClariVIT Wide Angle; Volk Optical Inc., Mentor, OH, USA) does not have a brim that Mini Quad has, and the head of the lens is cut (Figure 2). The cut design can prevent contacts of surgical devices, so that the scleral wound can be viewed within the visual field of microscope.

Both Mini Quad and ClariVIT produce an indirect image, so the inversion of the image is necessary. For the inversion of the image during surgery, SDI or Inverter tube is used. Table 1 shows comparison between

SDI (SDI: Stereoscopic Diagonal Inverter: Oculus, Lynnwood, Washington, USA) and Inverter tube (Inverter tube; Carl Zeiss Surgical GmbH, Oberkochen, Germany).

With SDI, the observed image quality is deteriorated by the addition of roof prism, and occationally desorption is necessary during cataract surgery.

Inverter tube is completely embedded in the lens tube so that the working distance does not increase, and it is not necessary to take an unnatural position during surgery.

Non-Contact Type

This type employs a similar method of viewing the ocular fundus by using a prefix lens in the slit-lamp microscope. Currently typical products include BIOM (Binocular Indirect Ophthalmoscope, Oculus Lynnwood,

Washington, USA -Figure 3) and OFFISS (Optical Fiber-Free Intravitreal Surgery System, Topcon, Tokyo, Japan). It is difficult to conduct surgical manipulations by viewing an indirect image as it is; therefore, the inversion of the image is necessary. Similarly to contact lens-type (contact-type) systems, surgery is performed by setting SDI or Inverter tube on the surgical microscope to invert the image. BIOM and OFFISS are explained below.

BIOM

Characteristics: An entire image of the ocular fundus can be seen during surgery without contact with the cornea. For rhegmatogenous retinal detachment, the break

region can be treated while checking the macular region. Also, when posterior vitreous detachment is prepared, it is possible to see the moment when a peripheral break is made, so a new break will not be missed. During fluid-air exchange and peripheral intraocular photocoagulation/freezing, it is not necessary to replace lenses, so that the overall visibility is improved, the safety can be secured, and the surgery time can be shortened. It is also useful for cases with opacity of the optic media and cases with small pupils.

Actual Use: To prevent dryness of the cornea, dispersive ophthalmic visco surgical devices are applied, and a small amount of BSS is placed thereon. First, the magnification of the surgical microscope is minimized. Next, the height of the surgical microscope is adjusted to bring the front lens at around 2-3 cm above the cornea of the patient.

The focus of BIOM is adjusted onto the device inserted into the eye or onto the retina. Next, the foot switch for the focus of the surgical microscope is lowered to adjust the front lens at around 1 cm above the cornea. The closer the cornea is, the wider the observation field becomes, but the front lens comes into contact with the cornea, and the lens is clouded due to the patient’s body temperature during surgery.

For the observation of the retinal peripheral region, the eyeball is rotated in the direction where the operator wants to see. X and Y of the microscope only have to be moved in

the direction to which the eyeball is rotated. This corresponds to the sense of the ordinary movement from the ergonomic standpoint, and accordingly the surgery is easy.

With contact lens-type (contact-type) systems, the ocular fundus cannot be seen when the eyeball is rotated. In addition, the directions of X and Y are opposite. For example, when the operator wants to see the right part, it is necessary to move the microscope to the left. This manipulation is opposite to the ordinary movement, and accordingly the operation is difficult.

During fluid-air exchange, water drops are easily adhered onto the front lens, so the manipulation is done a little distance away from the cornea. The device is inserted from the scleral wound under direct vision or, while viewing the wound through the front lens with the lens tube of the microscope lifted up, but it is easy to insert the device through 23G/25G trocar.

OFFISS

Characteristics: These instruments have proven to be of value, especially in complex cases such as eyes with difficult preretinal membranes and with small pupils.

An Optical fiber-free intravitreal surgery system (OFFISS) has been developed to facilitate the use of bimanual technique during vitreoretinal surgery with the 40-diopter

(D) lens.4 In addition, OFFISS has been developed for non-contact wide-angle vitreoretinal surgery with the 120-D lens. In this chapter we describe the wide-angle viewing system: OFFISS, 120-D lens, for vitreoretinal surgery.

This wide-angle viewing system consists of a 120-D aspheric lens and a prismatic inverting optical system (Figure 4). The 120-D aspheric lens is used as a field lens. It is attached to the microscope (OMS-800; Topcon, Tokyo, Japan), and vertical motion can be done by foot switch of microscope (Figure 5). The lens swings into place between the objective lens and the cornea,

and the microscope-mounted inverting device (SDI: Stereoscopic Diagonal Inverter) automatically erects the inverted image of OFFISS, 120-D (Figure 6).5 The Characteristic of OFFISS is that the position of field lens doesn’t change even if the microscope moves to focus, because it can independently move field lens and the microscope.

Actual Use: The 120-D lens was located about 5 mm above the cornea, where the fundus was clearly and widely visible. This rarely interfered with the surgeon’s manipulation of the micro-instruments for vitreoretinal surgery. To prevent dehydration of the corneal surface, the cornea was moistened with

dispersive ophthalmic viscosurgical devices, and aspirating speculum was very useful to prevent cloudiness by the dew condensation of the 120-D lens (Figure 7).

With the OFFISS, 120-D lens, the surgeon can practically see the entire fundus clearly. The field of view (over 130 degrees, Figure 8) is the same as the wide-angle contact lens (ClariVIT, MiniQuad, etc), and it almost observes the ora serrata (Figure 9).6 This system maintained a good view through a small pupil even when the vitreous cavity was filled with gas by fluid-air exchange.

Discussion

The Comparison with other wide-angle viewing systems confirms a very similar most wide field of view (Table 2).7 Furthermore, noncontact viewing systems have advantage over contact wide-angle viewing systems in that they avoid wicking or trapping blood between the lens and the cornea. This minimizes lost operation time for vitreoretinal surgery from cleaning the visual path.8,9

Table 2: Wide-Angle Viewing System Comparison Table

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Surgery and Diseases Vitreoretinaland Retinal