Retina Today - Choices of Wide-angle Viewing Systems for Modern Vitreoretinal Surgery (September 2012)

摘要

Wide-angle viewing systems (WAVs) are a useful fundus observation device for vitreous surgery, which been continually developed from the late 1980s to the present based on the indirect ophthalmoscopic principle.1-9 The WAVs not only offer a panoramic view of the surgical field but also improve the safety and efficiency of the surgical procedures.10,11 Surgeons can easily evaluate the fundus status and the location of retinal pathologies through the panoramic view, and engage the peripheral retina without requiring excessive rotation of the eyeball during surgery as was necessary when viewing the fundus through conventional floating prismatic lenses. In addition, the use of WAVs in conjunction with chandelier lighting allows easier bimanual maneuvers because these provide a view of the peripheral region without globe rotation, eliminating concerns regarding fragility of small-gauge instruments. 12 These tools may have played a part in the more widespread use of small-gauge vitrectomy for a variety of vitreoretinal pathologies, including challenging cases. At the same time, recently a variety of WAVs has been newly developed or upgraded from previous versions along with the recent widespread use of microincisional vitrectomy surgery (MIVS). Although the standard specification of each WAV such as the field angle of view is usually demonstrated in the brochures, the definition is often not identical among the manufactures. The optical design is the key industrial secret in each device, which will not be open to surgeons for comparison. In addition, the imaging quality (distortion) of the fundus view is not easy to quantitatively evaluate. Therefore, the differences of the viewing performances (field angle and imaging quality) have never been compared among the WAVs objectively. Here, we report a brief laboratory investigation for semiquantitatively assessing the field angle of view and imaging quality of a grating target in a human model eye viewed through a variety of commercially available WAVs. The aim of this article is to provide the reader with comprehensive information of the latest advances in WAVs for modern vitreous surgery. Construction of a Model Eye for Fundus Viewing Evaluation In the current study, we newly constructed a model eye that was originally made based on Gullstranda??s model of the human eye for evaluating the fundus visualizing qualities through refractive and diffractive multifocal IOLs.13 The body of the eye was made of metal, and the axial length was 24 mm (Figure 1A). The diameter of the pupil was 8 mm. The distance from the corneal anterior surface to the intraocular lens (IOL), if implanted, was 5 mm. The cornea was made of polymethylmethacrylate (PMMA). The anterior surface was aspheric, and the cornea was constructed to have a spherical aberration of 0.220 m, which is comparable to the mean value of human eyes with a pupil diameter of 6 mm. An angle scale for evaluating the field angle of view and a 1951 United States Air Force (USAF) test target (Edmund Optics) were glued to the posterior surface of the model eye up to the periphery of the retina (Figure 1B). The USAF target consisted of gratings of different orientations and spatial frequencies (Figure 1C).13 The model eye can be filled with balanced salt solution at room temperature or set under air conditioning for measurement. Fundus Imaging Analyses Through Wide-angle Viewing Systems Using the eye model, we studied five noncontact type WAVs: BIOM (Oculus), Merlin (Volk Optical, Inc.), OFFISS (Topcon Medical Inc.), Resight (Carl Zeiss Meditec AG), and Peyman-Wessels-Landers semi-wide angle viewing system (Ocular Instruments), and two contact WAV lenses, Clarivit and HRX (Volk Optical, Inc.) (Figure 2). The image through a flat-concave contact lens made of quartz glass (HHV, Hoya) was used as control for assessing the image qualities at the posterior pole. The IOL