David A. Wilkie, DVM, MS, DACVO
Spontaneous Lens Capsule Rupture
Occurs in cataracts associated with canine diabetes mellitus. Affected dogs have often been diabetic for only a few months with the onset of cataract on average only a month previously. The rupture occurs most often at the equator and is the result of rapid intumescence. Uveitis and intra-lenticular uveal pigment are common.
While surgeon opinion differs on pre-operative treatment and when to operate these patients, personally I have less respect for this preoperative change than in past. With new preoperative systemic NSAID's, phacoemulsification, viscoelastic agents I often treat these eyes for 24-48 hours prior to surgery and then operate.
A rare occurrence with current methods of presurgical patient preparation and cataract extraction. The use of intraoperative, intracameral 1:10,000 epinephrine, viscoelastics, and phacoemulsification, even those eyes with miosis can generally be persuaded to dilate once the anterior chamber is entered.
Intraoperative iris prolapse occurs in association with vitreous expansion, incorrect placement of the limbal incision, pre-surgical iritis, intraoperative iris trauma, and excessive irrigation fluid velocity. Placement of the incision slightly more anteriorly, decreasing infusion velocity, use of viscoelastic agents and gentle tissue handling will minimize the occurrence of iris prolapse.
Intraoperative use of 1:10,000 epinephrine, gentle tissue handling and use of viscoelastic agents has decreased the likelihood of hemorrhage. Postoperatively, tissue plasminogen activator may be considered. The surgeon must consider the possibility of a re-bleed associated with the use of TPA and consider a delay of 3-7 days prior to its administration.
Hard Nuclei / Aged Patients / Lens Instability
All of the above may be indications to consider the use of a 2-handed phaco technique. This can be planned with both incisions made at the onset of the surgery or the surgeon can convert intraoperatively. Use of a second instrument will shorten the phaco time and improve the surgeon's ability to stabilize, manipulate and divide the lens.
Lens Capsule: Radial Tears
Radial tears in the anterior capsule are best prevented. Perhaps one of the most critical aspects of cataract surgery, especially if IOL insertion is planned, is the capsulorhexis. Radial tears are associated with displacement of the IOL haptic out of the capsule bag and IOL decentration. Capsulorhexis is best performed using forceps and the continuous tear circular capsulorhexis approach (CTCC). Capsulorhexis is best performed prior to phacoemulsification as this will decrease the chance of creating a radial tear.
It has been demonstrated that the continuous tear circular capsulorhexis is the least likely to develop radial tears. CTCC will stretch 62% over its original diameter to facilitate implantation of an IOL before a radial tear will occur.
If a radial tear is discovered, it is best to attempt to bring this tear back into the central circular capsulorhexis, completing the circle and preventing extension of the tear.
If a radial tear is created and an IOL placed, the haptics should be directed as far from the radial tear as possible.
I prefer a 0.5mm or 0.7mm aspiration port and use a 45° curved I/A handpiece. The near cortex should be the first cortex removed. If you use a 2 handed technique the manipulating instrument can facilitate removal of the near cortex and help feed the aspirated cortex into the port.
Lens Capsule: Polishing, Opacities
Capsule polishing is an essential, but often ignored procedure due to the concern for iatrogenic capsular tears. Capsule polishing should be performed on both the anterior and posterior lens capsule. It is easiest to use a 0.3 mm or 0.5 mm I/A cannula at a low vacuum setting for the posterior capsule (40-50 mmHg), with higher vacuum settings possible for the anterior capsule (50-100 mmHg).
Opacities of the anterior and posterior capsule are more common in eyes with hypermature cataracts, with or without lens-induced uveitis. If possible, these opacities should be removed by thorough capsule vacuuming and polishing. If they cannot be removed, but are not in the visual axis, or are insignificant in size, then they may be left. Larger opacities, especially those in the visual axis may require removal by a planned posterior capsule capsulorhexis using Vannas scissors and Utrata forceps, or by use of a guillotine vitrector. Posterior capsulorhexis can be performed prior to or after IOL insertion using viscoelastic material to prevent vitreous presentation through the capsular tear. A planned CTCPC is also indicated for management of a persistent hyaloid associated with a cataract. Incise the posterior capsule using Vannas scissors, elevate the capsule from the vitreous face using viscoelastic and evaluate the patency of the hyaloid. Most are non-patent and can be cut without risk of hemorrhage.
Lens Capsule: Posterior Capsular Tears
Posterior capsular tears are best avoided rather than managed. If they occur it is essential to attempt to complete phacoemulsification away from the capsular tear to avoid enlarging it. Viscoelastic should be placed over the tear to tamponade the vitreous. The irrigation rate should be decreased and the irrigating fluid directed away from the posterior capsular tear. In many instances, it may be best to convert to a bimanual technique placing a separate infusion port into the anterior chamber. Finally, a small linear or triangular posterior capsular tear is best converted into a circular tear by means of a planned posterior circular capsulorhexis using Utrata capsule forceps.
The most common time for posterior capsular tears to occur includes during nucleus extraction (41%), posterior capsule polishing (28%) and irrigation/aspiration. The incidence of posterior capsular tears is approximately 5% for the inexperienced phaco surgeon, but decreases to <1% with experience.
The question of IOL placement must be addressed once all the lens material has been removed. If a small posterior capsule tear is present, but the remaining capsular bag is intact and stable an endocapsular IOL is preferred. An acrylic IOL that can be placed through a 3.2-3.6 mm incision will improve lens placement and minimize vitreous presentation. However, if the capsule disruption is severe then a posterior chamber IOL can be sutured in the ciliary sulcus.
Lens Capsule: Capsular Dialysis
If capsular instability is severe, capsulorhexis and phacoemulsification will be compromised and conversion to ECCE may be indicated. With zonular dialysis, phacoemulsification should be performed through a small capsule incision and the lens fragmented with a minimum of lateral movement. Care is taken to avoid progression of the dialysis. The capsulotomy is completed with scissors and not by tearing. Use of a 2-handed technique is advised.
Zonular dialyses are less common than posterior capsular tears. If a dialysis has occurred and an endocapsular IOL is to be placed, the ideal lens is one with a large optic and increased haptic-capsular contact (C loop or 360° haptic) In addition, the IOL should be inserted by pressure on the superior haptic and not by dialing. An acrylic IOL that can be placed through a 3.2-3.6 mm incision will improve lens placement. Alternatively, a posterior chamber IOL can be placed in the ciliary sulcus and sutured. This can be done using an ab-interno, ab-externo or modified ab-externo approach. I prefer the modified ab-externo approach if the lens has been removed through a 3.2 mm incision.
Cavitation / Bubbles
Cavitation is created by the process of phacoemulsification. This process results in the generation of bubbles which interfere with probe-lens contact and reduce cutting power and in addition, store energy which when the bubble implodes is released as high pressure, high temperature 'shockwaves' and induces free radicals, all of which can result in cell death.
Expanding Vitreous Syndrome/Vitreous Presentation
Expanding vitreous syndrome occurs in eyes with an intact or disrupted posterior lens capsule. It is seen most often in brachycephalic dogs. Clinically, the intact posterior lens capsule will be seen to be displaced anteriorly and in some instances will protrude through the anterior capsule opening and into the anterior chamber. If the posterior capsule has been disrupted, the vitreous will expand through the posterior capsule tear, enlarging the tear and entwining itself with the lens material and phaco aspiration port. Expanding vitreous syndrome in the presence of an intact posterior capsule can be minimized by use of a non-depolarizing neuromuscular blocking agent, by use of a lateral canthotomy and by ensuring external forces are not applied to the globe by the eyelid speculum, drapes, stay suture tension, or the surgeon once the anterior chamber has been entered. In addition, if the posterior lens capsule is observed to move anteriorly viscoelastic material should be introduced in an effort to force the capsule posteriorly. Failure to prevent or control expansion of the vitreous may result in an inability to insert an IOL or in extrusion of the IOL following implantation if the anterior capsulorhexis is too large.
Vitreous presentation will be encountered in eyes with posterior capsular tears and rupture of the anterior vitreous face, zonular dialysis (rupture) and lens subluxation, and in some eyes with vitreous degeneration. Although phacoemulsification has the advantage of maintaining the anterior chamber and anterior chamber pressure and thereby minimizing vitreous presentation, it also has the disadvantage of irrigation/aspiration. Vitreous may become hydrated and incarcerated into the phaco tip resulting in further disruption and loss of vitreous and interfering with removal of lens material. If a posterior capsular tear is observed, steps must first be taken to prevent enlargement of the tear and disruption of the vitreous face. In general, if vitreous is presented into the anterior chamber a partial vitrectomy is indicated. Many of today's phacoemulsification machines come with the ability to be expanded to include an oscillating and a guillotine vitrector. Vitrectomy can then easily be performed by exchanging handpieces while continuing to use the same tubing, infusion solution, and foot pedal. This allows for rapid conversion. In general, it is preferred to perform a dry or low flow bimanual vitrectomy using a separate infusion port rather than coaxial infusion. This will minimize further disruption of the posterior lens capsule and vitreous. Do not use the single port i/a cannula provided with your vitrector!
Displaced / Dislocated Lens Fragments
The questions to be asked include whether the retained material is cortical or nuclear? A small amount of residual nuclear lens material can be left in the vitreous with minimal reaction. Retained cortical material is more reactive however and must be removed.
In veterinary medicine, we do not have the luxury of closure and referral and we would prefer to avoid a pars plana approach if we are already in the anterior chamber for the purpose of phacoemulsification. Removal of the lens fragments can be performed through the limbal incision provided care is taken to avoid further disruption of the vitreous, or if the vitreous must be disturbed it should be done with appropriate instrumentation (not your phaco handpiece!). Viscoelastic material can be used to tamponade the vitreous to help prevent further disruption. As soon as a posterior capsular tear and displacement of a lens fragment is noted, infusion/aspiration should stop. A second entry wound is then made at the limbus for infusion and the infusion is directed into the anterior chamber, parallel with the iris and away from the vitreous. Lens material should not be fragmented in the vitreous using the phaco handpiece. If possible, the fragments are delivered into the anterior chamber at the level of the iris plane where they are fragmented. Alternatively, a vitrectomy handpiece can be used to aspirate and cut smaller lens material in the vitreous body. This is especially effective for cortical material and a guillotine vitrector works best. When performing a vitrectomy, a low flow bimanual technique is used or viscoelastic material is used to vault the chamber and a dry vitrectomy performed.
The question of IOL placement must be addressed once all the lens material has been removed. If a small posterior capsule tear is present, but the remaining capsular bag is intact and stable an endocapsular IOL is preferred. However, if the capsule disruption is severe then a posterior chamber IOL can be sutured in the ciliary sulcus.