CONTACT VERSUS NONCONTACT WIDE-FIELD VIEWING SYSTEMS: Why Not Have the Best of Both Worlds?
Current WAVs are divided into two main types: contact and noncontact systems. Both provide an inverted image that must be reinverted to allow correct visualization for the surgeon. Spitznas et al were the first to report the use of a stereodiagonal inverter to achieve a properly oriented view.1,2
In 1989, Avi Grinblat developed a panoramic system based on binocular indirect biomicroscopy, and in 1992, Chang described the contact wide-field viewing system at the Wacker Prize lecture of the Club Jules Gonin.
With contact systems, the wide-angle lens is placed directly on the cornea, which has been previously coated with viscoelastic polymer. The size of the field of view varies depending on the optical properties of the lens. The lens can be used with any microscope equipped with an image inverter, and it provides excellent visualization by reducing reflection from the corneal surface and avoiding inherent corneal aberrations and those related to ocular movement produced during manipulation of the instruments through the sclerotomies. Despite these excellent qualities, this system is not the most widely used in vitreoretinal surgery because of three essential factors. First, it requires the help of a highly trained assistant who spends most of the time manually positioning the lens to obtain the best possible visualization. Second, the microscope-viewing head must run a lengthy distance between the position needed for working on the macula (low position) and a position for working on a much larger field. This may exceed the total possible movement range of the head, and a second assistant is needed to manually adjust the height, with the consequent loss of time. Last, in complex cases requiring bimanual surgery, the operative field can become very “crowded,” including the assistant's hands positioning the wide-angle lens, the surgeon's hands, and sometimes the hands of a second assistant to position the chandelier light for best possible illumination/visualization.
As the name implies, with noncontact systems, the wide-angle lens is placed above the corneal surface, but there is no direct contact. The main advantages of this approach are that there is no need for an assistant to hold the lens in position, the eye can be rotated, and the size of the field of view can be changed by varying the distance from the lens to the cornea. However, there is a drawback: As the lens approaches the cornea, condensation can develop on the undersurface of the lens. In addition, corneal desiccation must be avoided by constantly applying viscoelastic material. Several measures have been described to manage these difficulties.3
In some situations, better visualization is obtained with noncontact than contact systems, especially in eyes with small pupils or over certain surfaces (e.g., osteo-odonto-keratoprostheses, Boston keratoprostheses, or temporary keratoprostheses). In other situations, however, contact systems provide higher quality vision and a larger field of view during surgery. Hence, it could be useful to device a way to enable the use of both these WAV options on the same instrument, depending on the requirements of each individual case. To our knowledge, there is only one previous report describing an approach to use both types of visualization, but it does not seem to have gained much popularity.