The Role of Capsular Tension Devices in Phaco
The Role of Capsular Tension Devices in Phaco
Adding safety and stability when zonular weakness is present.
BY ABDULLA NAQI, M.D., DIAMOND Y. TAM, M.D., JOSHUA C. TEICHMAN, M.D., AND IQBAL (IKE) K. AHMED, M.D.
Performing phacoemulsification in patients with significant zonular weakness presents many challenges. These patients are at an increased risk of intraoperative and postoperative complications, including vitreous prolapse, capsular rupture, retained lens material and postoperative IOL dislocation.
A number of management options exist for patients with zonulopathy. While standard phacoemulsification may be attempted, intracapsular extraction or lensectomy may also be surgical approaches considered. The use of a capsular tension device (CTD) as an intraoperative aid increases the likelihood of successful in-the-bag implantation of the IOL, and in many cases, completion of successful uncomplicated phacoemulsification. The options for location of IOL placement include the posterior chamber in-the-bag with or without a capsular tension device, sulcus-placed posterior chamber IOL, standard anterior chamber IOL (ACIOL), iris-claw IOL (Artisan, Ophtec, Boca Raton, Fla.), iris-sutured posterior chamber IOL or scleral-sutured posterior chamber IOL. The appropriate choice of placement is largely dependent on the integrity and status of the capsular bag following cataract extraction.
Indications for CTD Use
Pseudoexfoliation and traumatic lens displacement are the most common causes of zonular weakness. The decision to use a CTD is typically made during the preoperative visit. Careful history-taking may reveal inherited causes for zonular weakness and hence lens instability, including Marfan's syndrome,1 homocystinurea, Weill-Marchisani syndrome, microspherophakia,2 retinitis pigmentosa3 and lens coloboma.4 Past ocular history may reveal a history of glaucoma with pseudoexfoliation syndrome or zonular weakness or trauma from previous intraocular surgery. A hypermature cataract, post-vitrectomized eye and intraocular neoplasms are other causes of zonular weakness.
"The decision to use a CTD is typically made at the preoperative visit."
Assessment of Zonular Weakness
Once the decision has been made to proceed with phacoemulsification, careful assessment of zonular support should be conducted. Zonulopathy is categorized according to the extent of the zonular dialysis in number of clock hours,5-8 severity of generalized zonular instability and location of zonular weakness. The characteristics of the zonulopathy are important, as they may be suggestive of the underlying pathology. We describe a method of evaluating zonular instability below.
■ Preoperative assessment of extent of zonular weakness: With the eye maximally dilated, the lens is examined using the slit-lamp. Lens phacodonesis, which is graded from +1 to +4, lens decentration, lens edge (examined by swinging the slit-lamp completely to the opposite side of the lens), zonular dehiscence documented in clock hours and lens edge shape is noted.
If the lens edge is curved or rounded, then generalized zonulopathy is suspected. Conversely, a relatively straightened lens edge signifies a localized zonular dehiscence with probable normal zonular tension elsewhere. Due to the vertical positioning of the human eye during standing position, a superior zonular dehiscence usually warrants the use of capsular tension devices — possibly scleral-sutured — and support more than inferior localized zonular pathology.
At the conclusion of slit-lamp examination, the patient should be reclined on the examination chair and the lens examined with a light source, such as an indirect ophthalmoscope, for any degree of posterior movement toward the vitreous cavity.
Figure 1. Cataract with profound zonular weakness.
All Images are Courtesy of the Authors.
■ Intraoperative assessment: Zonular weakness can also be uncovered during surgery. One of the early indications of weak zonules is flaccidity of the anterior capsule, capsular wrinkling or infolding on initial puncture or ovalization of the continuous curvilinear capsulorrhexis. Movement of the entire lens during the capsulorrhexis, during phacoemulsification or tilting of the lens are all signs of moderate to severe zonulopathy (Figure 1).9
One must be cognizant that generalized zonulopathy, such as in pseudoexfoliation, may need to be managed differently from a traumatic cataract with segmental zonular damage and remaining normal zonules. The choice of the endocapsular support device may rely on this distinction.
Figure 2. Loading of capsular tension ring (CTR) into injector.
Standard Capsular Tension Ring
Known as the standard capsular tension ring (CTR), this open-ring structure is made of polymethylmethacrylate (PMMA) and has an oval-shaped cross section with eyelets at both free ends. The "ski tip" design of the end terminals aid in avoiding entrapment of the capsular equator on insertion and also allows for the placement of secondary instrumentation (Figure 2).
There are two types of CTRs commonly available in North America: the Morcher (Reform) ring (Morcher GmbH, Stuttgart, Germany) and the Ophtec (StabilEyes) (Ophtec, Boca Raton, Fla.) ring. The Morcher ring comes in three sizes based on an uncompressed diameter: 12.3 mm (compresses to 10 mm), 13 mm (compresses to 11 mm) and 14.5 mm (compresses to 12 mm). The Ophtec ring is available in a 13-mm ring (compresses to 11 mm) and a 12-mm ring (compresses to 10 mm). The Morcher and Ophtec CTRs each have a different corresponding injector.
The selection of CTR size is based on capsular bag dimensions. A larger capsular bag usually requires a larger ring. Many surgeons prefer to choose a slightly larger implant, with 13 mm being most common. At minimum, overlap of the end terminals is needed to provide complete circumferential support. The size of the capsular bag positively correlates with the globe's axial length.10 The corneal diameter is also an indicator of capsular bag size. On the basis of this information, white-to-white corneal measurement and axial measurements can be used as a guide to CTR sizing, although many surgeons advocate routinely using larger sizes to ensure adequate overlap of end terminals, especially in myopic eyes.
Function of the CTR
The diameter of the CTR chosen should be larger than that of the capsular bag, resulting in centrifugal force expanding the capsular equator and providing an equal distribution of force over the entire capsular circumference.11
The following is a summary of the function of CTR:
► expansion of the capsular equator
► buttress areas of weak zonules
► recruit and redistribute tension from existing zonules
► re-center a mildly subluxed capsular bag
► place tension on the posterior capsule to decrease incidence of posterior capsule opacification (PCO).
Contraindications to the CTR
There are certain situations where CTR implantation is absolutely contraindicated. Anterior radial or posterior tears in the capsule are instances where CTR insertion can be detrimental.12,13 In the case of a non-continuous capsulorrhexis, the centrifugal forces generated by the CTR may cause further extension of the capsular tears posteriorly and risk loss of the CTR into the posterior segment.14
Cionni's Modified CTR
When the zonulopathy is extensive and the lens is severely subluxed, the standard CTR will not be able to provide adequate centration of the capsular bag. In 1998, Robert Cionni, M.D., developed the modified-CTR. This implant provides a solution to extensive and/or progressive zonular damage by allowing the surgeon to anchor the capsule bag to the eye wall.
The Cionni modified-CTR is an open-ring design with one (model 1-L) or two (model 2-L) fixation eyelets attached to the central ring. The eyelets, which allow the ring to be sutured to the sclera, protrude 0.25 mm forward from the body of the CTR and thus sit anterior to the anterior capsule, thereby conserving the capsular bag's integrity on suturing (Figure 4).2 It is important to ensure a minimum of a 5.5-mm capsulorrhexis, otherwise the islet of the ring may be too far anterior and cause iris chafing. Due to the design of the M-CTR, it is not easy to insert the device prior to the removal of the lens when it sometimes is most needed for stabilization. Furthermore, the two-eyelet model with two sets of looped sutures can be somewhat difficult to implant within the capsular bag.
Figure 4. Cionni modified-CTR, with a looped 9-0 polypropylene through eyelet being dialed into capsular bag.
Figure 5. Early insertion of the CTS without the requirement of dialing in.
Capsular Tension Segment
The capsular tension segment (CTS), designed by Ike Ahmed, M.D., in 2002 and manufactured by Morcher GmbH, is also intended for patients with profound zonular insufficiency.15 It is designed for cases requiring intraoperative support for significant zonular weakness, or for patients in need of long-term postoperative centration of an IOL within the capsular bag. This partial PMMA ring segment is 120° of arc length with a radius of curvature of 5 mm and, like the M-CTR, also possesses an anteriorly positioned fixation eyelet.
The CTS may be implanted without a dialing technique and thus transmits less force to the zonular apparatus (Figure 5). The CTS is designed to slide into the capsular bag with minimal trauma and thus may be used in cases of a discontinuous capsulorrhexis, anterior capsule tear or a posterior capsule rent. It is inserted into the capsular bag after capsulorrhexis and placed in the area of zonular weakness. The CTS may be used early in a case before the removal of the cataract.
The main body of the device sits inside the capsular bag supporting and extending the capsular equator with the central eyelet remaining anterior to the anterior capsule. When used for intraoperative support, an inverted iris retractor via a paracentesis incision is placed through the eyelet acting like a coat hanger to support the capsule in the area of zonular weakness (Figure 6a).
Figure 6a. CTS with iris retractor through the eyelet for intraoperative stabilization.
It should be distinguished that the CTS provides support in the transverse plane when sutured to the scleral wall. When circumferential support is also required, a CTR may be implanted in conjunction with already positioned CTS. (Figure 6b) The CTS is sutured to the sclera through an ab externo technique using a 9-0 polypropylene suture8 (Figures 7a and 7b). One or more segments may be used to obtain satisfactory IOL stability.
Figure 6b. CTR injected after placement of two CTSs that have been supported with iris retractors during surgery.
Figure 7a. Ab-externo suturing of the CTS using a 26-gauge hypodermic needle and 9-0 polypropylene suture. Here, the CTS has been moved to the center of the anterior chamber, with an initial pass having been made through the fixation eyelet. A second adjacent pass is made to create a suture loop.
Figure 7b. CTS looped with 9-0 polypropylene suture placed through a scleral groove in the area of greatest zonular weakness. With tension on the suture, the CTS will be support the capsular bag in the area of zonular loss.
Which Device to Use?
Nonprogressive zonulopathy such as traumatic or iatrogenic zonular dialysis and zonular coloboma in which the degree of zonular instability is minimal are well suited for standard CTRs, as the remaining zonules are typically of normal tension. With redistribution of these forces with the CTR, adequate support of the capsular bag can usually be attained.16
In progressive cases such as advanced pseudoexfoliation syndrome or Marfan's syndrome, however, a scleral-sutured M-CTR or CTS may be required for adequate long-term IOL stability and centration (Figure 8). Although patients with mild pseudoexfoliation are good candidates for CTR implantation, pseudoexfoliation is a progressive zonulopathy and consideration should be given to using adjunctive sutured CTS in cases of more profound zonular instability. These patients are at an increased risk for intraoperative complications as well as postoperative IOL dislocation, especially from superior zonular dialysis.17 Postoperative capsular phimosis is also a contributing factor to progressive zonular dehiscence in pseudoexfoliation syndrome. Even with CTR implantation, a seemingly stable IOL at the time of surgery may dislocate years later.8
Figure 8. Sutured CTS in place at the 4:30 position with well-centered PCIOL within capsular bag postoperatively.
|"CTDs reduce the risk of intraoperative and postoperative complications and improve patient outcomes."|
CTDs for Safety and Stability
Cataract surgery has transformed over the last 15 years from large-incision lensectomy to sutureless small-incision phacoemulsification. Capsular support devices and understanding of zonular behavior and pathology likewise have improved. Capsular tension devices reduce the risk of intra-operative and postoperative complications and improve patient outcomes. When faced with a case of suspected or confirmed zonular weakness, capsular tension devices should be used in order to ensure safe removal of the crystalline lens as well as adequate and stable placement of the IOL for long term centration and stability. OM
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- Hayashi K, Hayashi H, Matsuo K, et al. Anterior capsular contraction and intraocular lens dislocation after implant surgery in eyes with retinitis pigmentosa. Ophthalmology. 1998;105:1239-1243.
- Mizuno H, Yamada J, Nishiura M, et al. Capsular tension ring use in a patient with congenital coloboma of the lens. J Cataract Refract Surg. 2004;30:503-506.
- Jacob S, Agarwal A, Agarwal A, et al. Efficacy of a capsular tension ring for phacoemulsification in eyes with zonular dialysis. J Cataract Refract Surg. 2003;29:315-321.
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- Vass C, Menapace R, Schetterer K, et al. Prediction of pseudophakic capsular bag diameter based on biometric variables. J Cataract Refract Surg. 1999;25:1376-1381.
- Leger U, Witschel BM, Lim SJ, et al. The capsular ring: a new device for complicated cataract surgery. Presented at the third American-International Congress on Cataract, IOL and Refractive Surgery. May 11, 1993; Seattle, WA.
- Bopp S, Lucke K. Chronic cystoid macular edema in an eye with a capsule defect and posteriorly dislocated capsular tension ring. J Cataract Refract Surg. 2003;29:603-608.
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- Ahmed IK, Butler M. Capsular Tension Devices for the Glaucoma Surgeon. In: Glaucoma Today. Nov-Dec 2004:1-4.
- Jehan FS, Mamalis N, Crandall AS. Spontaneous late dislocation of intraocular lens within the capsular bag in pseudoexfoliation patients. Ophthalmology. 2001;108:1727-1731.
|Iqbal Ike K. Ahmed, M.D., is assistant professor at the University of Toronto in Ontario. Abdulla Naqi, M.D., Diamond Y Tam, M.D., Joshua C. Teichman, M.D., are all affiliated withe the University of Toronto, Ontario, Canada. None of the authors have any financial interests to report in regard to the products mentioned in this article.|
Ophthamology Management, Issue: January 2008