Evaluation of two techniques for irrigation/aspiration retrolental viscoelastic removal in cataract surgery

Author(s): Fernando Aguirre Balsalobre*, Paz Orts Vila, Fernando Hernández Pardines, Víctor García Conca, Sara Núñez Márquez and José Ramón Hueso Abancéns Purpose: To compare surgical results after phacoemulsification using two different techniques for removal of Ophthalmic Viscoelastic Device (OVD). Methods: A randomized prospective study was conducted on 77 patients who underwent cataract surgery. In the first group, OVD was removed over the optic by small abrupt horizontal and vertical displacements of the IOL. In ... Abstract View Full Article View DOI: 10.17352/2455-1414.000067


Introduction
The use of Ophthalmic Viscoelastic Devices (OVD) is a common practice in modern cataract surgery. Several viscoelastic substances with different physical and mechanical behaviour are commercially available at the moment. Dispersive viscoelastic agents are preferred to perform the earliest stages The third type of OVD available is viscoadaptative OVD, also diffi cult to remove from the anterior chamber, more than dispersive OVD for some authors [5] and slightly easier according to others [6]. Viscoadaptative OVD is also suitable to perform Arshinoff's Shell Technique (SST).
Capsule expansion before (intraocular lens) IOL implantation is preferred to be performed by using a cohesive OVD as it can be removed faster. High density OVDs are rarely used for this step.
It is a broadly accepted principle for cataract surgeons not to leave any foreign substances inside the eye after surgery. Complications such as postoperative increase of IOP, amongst others [7] have been reported when OVD has only been removed partially from the Anterior Chamber (AC).
Nevertheless, thorough aspiration of OVD, especially if located behind the IOL can be challenging. In our clinical setting, most surgeons perform I/A aspiration only within the anterior aspect of the eye, over the IOL.
To help retrolental viscoelastic evacuation, small sudden taps on the optic of the IOL can be performed both in a horizontal and vertical motion. Despite this manoeuvre, remaining viscoelastic can often be found between the IOL and the posterior capsule.
Remaining OVD trapped behind the IOL can alternatively be removed by placing the Irrigation/Aspiration (I/A) tip posteriorly, letting the aspiration port face upwards throughout the whole process to avoid inadverted capture of the posterior capsule.
The aim of the comparative study below is to analyse the outcome, in our hands, of both surgical techniques.

Material and methods
A randomized prospective study was conducted on patients undergoing cataract surgery at San Juan University Hospital (Alicante, Spain). Patients were consecutively included in one group or the other. The fi rst patient in group 1, the next patient in group 2, and so on. Thus, patients whose order of inclusion in the study was odd were included in group 1, and pairs in group 2.
Patients with history of Ocular surgery, including intravitreal injections, were excluded, as well as those diagnosed with ocular conditions such as corneal distrophies, ocular hypertension, glaucoma, retinopathy, pigment dispersion and pseudoexfoliation. Patients with idiosyncrasies that made us suspect a non-straightforward surgery or those standing higher than average likelihood of complications (lack of cooperation, poor mydriasis, concomitant limbal incisions, implantation of toric lens) were not included either Eyes with extremely high or low axial length or keratometry measurements, and those which required corneal suture or anaesthetic techniques other than topical + intracameral were also excluded from our study.
In the fi rst group OVD removal was performed by I/A aspiration over the IOL. Following the IOL implantation the I/A hand piece was used to remove as much OVD as possible from the anterior aspect of the eye by slightly shifting and tilting the IOL with the tip. Small sudden touches on the lens were also performed both horizontally and vertically as well as controlled partial decompressions to cause the anterior chamber (AC) to collapse and force evacuation of the OVD remainings entrapped posteriorly.
In the second group, during OVD removal, the I/A probe was not only placed in the AC but also behind the IOL, keeping the aspiration Port visible at all time as a safety measure.
The exact same protocol was used for all patients. Preoperative tests performed were: thorough interview with the patient about personal and family history of ophthalmic and general conditions, best corrected visual acuity, IOP, slit lamp examination, LOCS III cataract classifi cation, fundus examination, eye alignment tests, lacrimal irrigation, endothelial cell count, autorefraction/autokeratometry (Topcon KR8900, U.S.A.), AC Optic Coherence Tomography (OCT) to measure AC depth and angle to angle distance (Visante OCT-Carl Zeiss, Dublin, CA) and ultrasound biometry for IOL calculation and axial length measurements (OcuScan RxP Alcon laboratories UK).
In all cases of both groups was used the intraocular lens Lentis L-313 (Oculentis, Germany).
The preoperative assessment performed by the anesthesiology Department consisted on blood tests, EKG, chest x-ray, and clinical interview.
During 3 days prior the surgery, all patients followed the same lid hygiene routine as well as a prophylactic treatment with diclofenac and moxifl oxacin drops. The day of the surgery tropicamide, cyclopentolate and phenylephrine were instilled to achieve and maintain maximum mydriasis.
Chronologically all surgical steps where as follows: Patient was requested to lay down in supine position. Numbing drops (oxybuprocain 1 mg/ml plus tetracaine 4 mg/ml) were administered. A disinfectant solution (Betadine) was applied on the surgical fi eld. After that, an sterile fenestrated drape was placed over the patient's eye, always trying to keep the eyelashes away from the surgical fi eld. An ophthalmic speculum was adapted to the patient's lid to maintain the eye open and avoid the eyelashes to interfere with the surgery.
A 1 millimetre or smaller paracentesis is then performed. Dispersive OVD is placed into the AC to stabilize the eye in order to tailor a 2.2 millimetre wound, preferably in the steepest axis, when possible.
After that, the AC is refi lled with high density cohesive OVD in order to facilitate a straightforward continuous curvilinear capsulorrexhis within the limits of the optic area of the IOL, after which, hydrodissection and hydrodelineation are OVD removal was performed using one of the methods  Eye features were also similar in axial length, keratometry, IOP, spherical equivalent, AC depth (Table 1).
No clinically and /or statistically signifi cant differences were found between the two groups in IOP, refractive error and IOL position ( Table 2).
Refractive changes along the 6 fi rst postoperative weeks were 0,33 D for group 1 (AC only OVD removal) and 0,28 for group 2 (retrolental OVD removal). P= 0,38 (Table 3).  Postoperative IOL position shifting after the 6 fi rst weeks after the surgery was 0,18mm in the fi rst group and 0,11 in the second group. This subtle difference did not reach statistical signifi cance (P= 0,057) ( Table 3).
In all groups compared, the samples followed a normal distribution. Data was analyzed using Levene test for equality of variances. There were no surgical complications secondary to the OVD removal techniques described above. No patient presented postoperative increase of IOP at the fi rst followup appointment after surgery. No steroid responsive ocular hypertension or postoperative uveitis was described either.

Discussion
Even though AC maintainer devices are available in order to diminish intrasurgical IOP fl uctuations during all phases of the surgery and expand the bag in order to avoid AC to collapse [8,9], most surgeons prefer to use OVD for that purpose.
Low density cohesive OVD are used preferably for bag expansion before IOL implantation, because its aspiration is easier and they tend to produce less IOP spikes after surgery [10][11][12][13]. In our study, we used a low density cohesive OVD for the last phases of the surgery.
Despite OVD aspiration only from the middle of the AC with no manipulation of the IOL, it is known to be ineffective to achieve complete evacuation [14], authors have not agreed yet on the gold standard technique for this step of the surgery.
According to the literature reviewed, there are several valid techniques when it comes to OVD removal: the fi rst method would be OVD aspiration from the AC by subtle and sudden taps on the IOL surface [15,16]. The second method is the "Rock and  [4,17]. This maneuver involves the potential risk of entrapment of the posterior capsule and its subsequent rupture.
It has been described and it's accepted that the material the IOL is made of can infl uence on the technique chosen to remove OVD [10,11] It has been suggested that the remaining intracapsular OVD can also be associated with postoperative capsular blocks.
Although recent studies shows that capsular blocks can be also signifi cantly infl uenced by the axial length and the type of IOL used [18], laboratory examination of the retrolental fl uid has found viscoelastic material [19]. Some patients experience spontaneous resolution [20] but most of them require posterior and peripheral anterior YAG capsulotomy [21].
Patients with postoperative capsular block show an unexpected myopic shift [22]. Following the same reasoning, during these maneuver. However, the possibility of rupture of the posterior capsule by the I/A probe is a well-known fact [23,24].
The main weakness of this study was the lack of clear visualization of OVD after completing I/A OVD aspiration.
Besides, a longer follow-up period would be necessary in order to assess late capsular block, capsular opacifi cation, or potential increased risk of chronic endopththalmitis. A more numerous sample would have been useful to confi rm results.
Based on the results we obtained, we can conclude that, OVD material can be removed from the eye by only aspirating from the centre of the AC at the end of the surgery when a platehaptic IOL has been implanted. Remaining OVD behind the lens do not produce rise in IOP, refractive changes, or modifi cation of the IOL position after surgery in a 6 weeks long follow-up.