Ophthalmic Viscosurgical Devices (OVDs) in Challenging Cases: a Review

OVDs have become indispensable tools in modern cataract surgery, having a great impact on the success of the surgical procedure and on the IOL preparation/implantation process [7]. Several OVD types can be used for different purposes and at different stages during surgery. For example, the use of a cohesive OVD can help to enlarge a small and unresponsive pupil, to smooth the front capsule [17, 20‐23], and to create space by deepening the anterior chamber, whereas a dispersive OVD is the best option to protect the corneal endothelium over a longer period [8, 19, 21, 22, 24]. A dispersive OVD is also needed when preparing an IOL, lubricating a cartridge, or folding a lens, but it is more difficult to be removed from the eye and more likely to increase the IOP [16, 18, 23, 24, 26]. For these reasons, there are also systems containing both types of OVD, cohesive and dispersive, as previously mentioned [7, 18, 29, 30]. Likewise, there are specific surgical strategies, such as the soft-shell technique [31], which use both OVD types in layers on top of each other. The goal of all these approaches is always to combine the advantages of cohesive and dispersive substances.

The selection of the appropriate OVDs is especially crucial in complex or challenging cases, such as in hard cataracts [11, 32], flat anterior chambers [12], narrow pupils and the pseudoexfoliation syndrome [33], intraoperative floppy iris syndrome [34], disinserted zonular fibers [34], Fuchs endothelial dystrophy [34], small holes in the posterior capsule with protruding vitreous [34], and hypotonic eyes due to previous glaucoma surgeries [35]. Indeed, the type of OVDs used in such cases may determine the success of the surgery, the postoperative outcome, and consequently the overall patient satisfaction. For this reason, it is important to know the OVDs commercially available and to understand their properties, leading to different advantages and disadvantages.

Cataract surgery in eyes with hard brown cataract or Brunescent and Morgagnian cataracts remains a challenge for eye surgeons because of the higher risk of complications, such as nucleus drop, posterior capsule rupture, corneal burn, and corneal endothelial damage [11, 32]. Of particular relevance are the potential effects of the longer surgical maneuvers and the higher levels of ultrasound energy commonly used in these cases on the corneal endothelium [36, 37]. For this reason, the use of dispersive OVDs seems to be an adequate option to achieve an optimal endothelial protective effect [32], although the use of combined agents may be adequate to facilitate also some surgical steps [38]. Toprak and Yaylali [11] described in 2019 two maneuvers to be used in different steps of phacoemulsification surgery in hard cataracts, providing debulking of the central dense nucleus and preventing posterior capsule rupture. These authors recommended the use of a cohesive OVD to fill the anterior chamber and to protect the corneal endothelium. Likewise, the OVD was used to inflate the capsular bag before IOL insertion, retreating the posterior capsule backward and safety preventing the rupture of this thin layer [11]. Yuan et al. [32] described the use of a cohesive OVD (sodium hyaluronate 1.5% at a molecular weight of 2,000,000 to 2,500,000 Da) to facilitate the extraction of the nucleus of a hard cataract. Specifically, the authors described a technique in which, after dislocation of the nucleus into the anterior chamber and OVD injection to protect the corneal endothelium and expand the capsular bag, the OVD cannula was passed beneath the nucleus, where more OVD was injected to promote its lifting. Subsequently, some pressure was applied to the posterior lip of the tunnel incision by the angle of the OVD needle, which allowed smooth extraction of the nucleus with the efflux of the OVD [32].

In a case series, Miyata and coauthors [38] demonstrated the safety and efficacy of corneal endothelial protection using the soft-shell technique (Healon + Viscoat) in hard-nucleus cataract eyes undergoing phacoemulsification surgery. Fasce and colleagues [39] confirmed in a randomized controlled clinical trial that the use of a viscoadaptive OVD (BD Multivisc) was as effective as the soft-shell technique (Biolon + Viscoat) in protecting the corneal endothelium in Fuchs dystrophy during phacoemulsification in patients with hard lens nucleus.

Moreover, it has been shown that viscodissection (rather than hydrodissection) in cases with very loose zonules (e.g., pseudoexfoliation, posttraumatic) is a safe and effective technique, minimizing the risk of zonulolysis.

The pseudoexfoliation syndrome (PSX) is a complex age-related disorder characterized by the progressive accumulation of abnormal extracellular pseudoexfoliative material in ocular tissues, including the ciliary body, iris, iridocorneal angle, and lens capsule [40]. This may complicate the performance of cataract surgery due to pupillary abnormalities generated by this condition, such as significant miosis and a limitation of the dynamic pupillary pattern [40]. Indeed, iris hooks or Malyugin rings are sometimes needed for a mechanical pupil dilation allowing the surgeon to have an adequate visualization of the anterior segment [41]. A new tool to facilitate the surgical procedure in eyes with PSX and not reacting pupils is the use of an OVD combined with a staining agent [33]. Currently, there is only one commercially available system based on this concept that combines a sodium hyaluronate OVD with trypan blue, Pe-Ha-Blue® PLUS (Albomed GmbH, Schwarzenbruck, Germany). It is available in a prefilled syringe to allow for the simultaneous administration of the OVD and staining agent in one single step [33]. The aim of this blue-colored OVD is to deepen the anterior chamber, to protect the corneal endothelium, and simultaneously to stain the capsule, facilitating the creation of the continuous curvilinear capsulorhexis and surgery, and consequently minimizing the time needed for the procedure. A recent comparative case series has demonstrated that the use of this blue-colored OVD in PSX eyes with not reacting pupils can provide a statistically significant time gain in terms of surgery duration compared to the use of a standard clear OVD, with additional potential benefits in surgeon satisfaction, postoperative corrected distance visual acuity and IOP, as blue OVD remnants can be identified and removed more easily [33].

In 2005, Chang and Campbell first described the intraoperative floppy iris syndrome (IFIS) in patients with benign prostatic hyperplasia and systemic administration of alpha-A1 adrenoceptor antagonist tamsulosin [42]. This condition is characterized by a loss of the iris muscle tone leading to significant pupil constriction despite pupil dilatation with standard mydriatic drugs before the initiation of cataract surgery. IFIS can lead to an increased complication rate in this type of eye surgery due to fluttering and billowing of the iris stroma caused by ordinary intraocular fluid flows, a marked tendency for the iris to prolapse toward the side port incisions, and progressive constriction of the pupil during surgery [43]. All these signs are accompanied by suboptimal pupillary dilation in response to preoperative mydriatic protocols [42]. In addition, pupillary stretching techniques are ineffective because of the floppy, easily stretched nature of the pupil margin [42, 44]. Since incision leakage through the clear-cornea incisions can further promote the IFIS effect, tight incisions and longer tunnels are essential in these cases when performing cataract surgery [44].

Chang recommended the use of iris hooks or other mechanical devices intraoperatively for pupillary dilation, such as the Malyugin ring [45]. However, a failure to detect IFIS before the performance of the capsulorhexis might make the use of these instruments more difficult [45]. Chang and Campbell found Healon 5 (Johnson & Johnson, Santa Ana, CA) to be useful in IFIS, not mentioning the use of more elaborate multiple-OVD techniques [42]. Steve A. Arshinoff described the use of OVD combinations in IFIS following two different techniques, tri-soft shell (TST) [34] and ultimate soft-shell technique (USST) [46]. As previously mentioned, the soft-shell technique consists of using two viscoelastic agents simultaneously to achieve a better iris stabilization during the entire procedure [31]. With this technique, the anterior chamber is first covered with a dispersive OVD by 75%. Afterwards, a cohesive OVD is injected onto the surface of the anterior lens capsule in the middle of the anterior chamber, maintaining the boundary between the cohesive and dispersive OVD at the pupil edge. This maneuver pushes the dispersive OVD up and out and stops the movement of the pupil (rigid OVD roof) [31].

The USST is a modification of the soft-shell technique consisting of compartmentalizing the anterior chamber using low-viscosity fluids, such as balanced salt solution or trypan blue, in combination with a viscoadaptive OVD, such as Healon 5 (sodium hyaluronate 2.3%) or I-Visc Phaco (sodium hyaluronate 2.5%) [46]. The use of this technique facilitates the surgical procedure owing to the effect of the viscoadaptive OVD and OVD removal at the end of the procedure [46]. In 2006, a combination variant of the soft-shell technique and USST was described, in which the flow parameters were adjusted [47]. The TST approach is a generalization of all these previously described soft-shell concepts [34]. The first step is to inject the dispersive OVD through the phaco-incision to form a central mound on the anterior capsule surface, stopping the injection once the anterior chamber is approximately 20–25% full. After this, a cohesive or viscoadaptive OVD is injected beneath the dispersive OVD onto the anterior capsule, displacing the dispersive OVD upward against the endothelial surface of the cornea. The injection of the second OVD is continued until the pupil stops dilating and before the eye becomes firm. With these maneuvers, a low-viscosity protective outer dispersive OVD shell is generated that encircles a cohesive or a viscoadaptive OVD pressurizing and stabilizing the inner shell previously created. Injection of balanced salt solution or lidocaine-phenylephrine is then performed slowly beneath the viscoadaptive OVD to create a continuous low-viscosity fluid on the lenticular surface, with the pupillary margin as the peripheral border. Consequently, the viscoadaptive shell is displaced upwards acting as a central bridge [34]. With this procedure, maximum control over the operative environment is achieved in IFIS eyes, minimizing the incidence of complications [34].

Local anesthetic agents block the conduction of nerve impulses by acting directly on voltage-gated sodium channels. Intracameral injection of lidocaine affects all nerve fibers in the anterior chamber to some degree, causing anesthesia and akinesia of the iris. Several studies showed that the use of intracameral injection of lidocaine 1% as coadjuvant medication helps to achieve pupil dilatation [48, 49]. The intracameral anesthesia effect and OVD function maintenance of the anatomical space and protection of surrounding tissues were also combined in one single step [50‐53]. One example of this type of combined system is VisThesia (Carl Zeiss Meditec, Jena, Germany) which combines 2% lidocaine and 0.3% sodium hyaluronate (volume 0.4 ml) provided in individual plastic blister packs [50‐52]. This type of system may provide more comfort to patients, making the application of the anesthetic easy [50]. In fact, there is some scientific evidence of the superiority of the use of VisThesia compared to the conventional procedure in terms of intraoperative pain [50]. Some colleagues have reported a greater increase in macular thickness with the use of VisThesia [50] as well as a greater reduction of corneal endothelial cell density compared to the use of conventional OVDs [50, 51]. But results are contradictory with some other authors that showed no greater reduction of endothelial cell count with the use of VisThesia [52]. In 2008, Auffarth GU and Borkenstein AF presented at the annual conferences of ESCRS (Berlin) and DGII (Heidelberg) the results of their prospective safety study and showed no negative effect on endothelial cell count. More research is still needed to confirm the potential benefits and risks of the use of viscoanesthesia in cataract surgery as well as the most appropriate indications for this modality of OVD.

The formation of a significantly flat anterior chamber is a complication associated with eyes that have had previous glaucoma surgery [54]. One condition leading to this situation is the presence of overfiltration after trabeculectomy with mitomycin C, which has been shown to have an incidence of around 24% [54]. The persistence of a flat anterior chamber in the eye can cause further complications, such as peripheral anterior synechiae or endothelial dysfunction [54]. For this reason, this condition must be treated, for which various pharmacologic (atropine, phenylephrine, and in selected cases orally administered acetazolamide) and surgical options are available [55, 56]. One of these options is the injection of OVD into the anterior chamber, first described in 1982 by Fisher et al. [57] using sodium hyaluronate. Some years later, the successful use of a viscoadaptive OVD (Healon 5) to treat a flat anterior chamber after trabeculectomy was reported [58], as well as the application of dispersive OVDs [12]. However, the long-term success rate with OVD injection in these cases has been demonstrated to be relatively low [12]. For this reason, combinations of OVD with other stabilizing substances have been tested, such as the combination of Healon and sulfur hexafluoride [59].

From the prophylactic perspective, intracameral injection of 2% hydroxypropyl methylcellulose during trabeculectomy has been shown to maintain the anterior chamber depth, minimizing complications related to anterior chamber shallowing after trabeculectomy [60].

In this relatively new field OVD is used for protection of corneal endothelium during posterior lamellar graft preparation and viscodissection.