diameter of 0.89 mm or less, smaller than the 0.91 mm diameter of a 20-gauge vitrector. Furthermore, the GRIN lenses offer higher resolution than fused-fiber endoscopes [119].

10.3.4Applications of Intraocular Endoscopy

In recent years, more applications for intraocular endoscopy have been described in the literature. The most obvious utility of an endoscope in vitreoretinal surgery is visualization and manipulation of the vitreous cavity and retina through opaque media. Yet endoscopy has also been advocated for eyes as an adjunct to traditional surgery with an operating microscope, not only for direct visualization during vitrectomy, but also for intraoperative and postoperative inspection of wounds and other difficult-to-visualize areas of the posterior segment.

10.3.4.1 Media Opacity

Vitreoretinal procedures such as retinal detachment repair in patients with ocular media opacity often require extensive intervention. Corneal opacity may require simultaneous or staged penetrating keratoplasty, temporary keratoprosthesis, or open sky vitrectomy. Presence of cataract may necessitate concomitant lens extraction. Additionally, eyes with previous surgical or nonsurgical trauma may have disruption of anterior chamber anatomy, including fibrosis and synechiae causing miosis, retrocorneal or retrolental membranes [112]. Endoscopy may be advantageous in these situations in reducing surgical manipulation of the eye.

Certain patients with retinal detachment may benefit from endoscopic surgery, especially those with little or no expected PVR, or those with opacity that could be expected to either resolve spontaneously or with medical therapy, or in those patients where surgical management of anterior segment pathology might be anticipated to be harmful to the eye or delay healing [122]. Successful endoscopic retinal detachment repair has been described in patients with significant corneal edema where keratoprosthesis or penetrating keratoplasty might have been considered. In these instances, it is suggested that proceeding with endoscopic

surgery may prevent further corneal endothelial damage and ultimately corneal endothelial failure [123].

In cases of endophthalmitis, visualization of the posterior segment is often significantly impaired, and there is considerable risk of damage to ocular structures when visibility is poor. A technique of combined microscopic and endoscopic vitrectomy has been described, in which core vitrectomy is performed using an operating microscope to create a clear fluid-filled pocket, followed by endoscope-guided vitrectomy for the remainder of the dissection, allowing for more controlled identification of anatomic landmarks within the eye [124].

Proliferative diabetic retinopathy poses a challenge, as neovascularization of the anterior segment can cause hyphema and fibrovascular proliferation and scarring as well as miosis that hamper visualization of the retina and vitreous using traditional wide-angle viewing systems [125, 126]. Though these issues may be dealt withusingdifferentmodalities,includingiris-expansion devices or anterior chamber washout, approaching a case endoscopically may be a potentially less traumatic modality, reducing the surgical burden on the eye. Of note, eyes undergoing traditional three-port vitrectomy using an operating microscope are not precluded from the use of endoscopic viewing should there be unanticipated issues or complications that arise, such as anterior tractional detachment or intraoperative hyphema [125].

10.3.4.2Subretinal Fluid Drainage and Fluid–Gas Exchange

Subretinal fluid can be drained effectively through existing retinal breaks during fluid–gas exchange. However, this method can present several challenges to visualization; there can be glare and disturbances from the fluid–gas interface; additionally, if a primary retinal break is in the far periphery, direct visualization of fluid drainage under microscopy can be extremely difficult without creating a secondary posterior drainage retinotomy, which may lead to secondary proliferative vitreoretinopathy [112, 113]. Endoscopic subretinal fluid drainage with appropriate head positioning to allow for fluid to easily come out of a peripheral break has been described. This method obviates the need for a drainage retinotomy, and the process, extremely difficult to see with an operating microscope, may be