Iris Claw IOL Fixation—Our Technique






CHAPTER


59


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IRIS CLAW IOL FIXATION


OUR TECHNIQUE


Ravijit Singh, MS; Kiranjit Singh, MS; Harmit Kaur, MS; Indu Singh, MS; and Daljit Singh, MS, DSc


The iris claw, or Artisan, lens is an entirely unique genre of intraocular lenses (IOLs) that does not need the angle of the anterior chamber, ciliary sulcus, sclera, or capsular bag for support. Instead, it is fixated to the iris muscle, either to the front or back surface. Fixation to the back surface of the iris is referred to as retropupillary fixation. Although this IOL was originally designed to be fixated to the anterior surface of the iris, in this chapter, we shall be concentrating mainly on the technique of retropupillary fixation of the iris claw lens.


History of Design of the Iris Claw Lens


Before we start with the technique of implantation of the iris claw lens, it is important that we delve into the design of the lens. Designed by legendary Dutch ophthalmologist Dr. Jan Worst in the early 1970s, the basic design of the iris claw lens has remained unchanged for nearly 4.5 decades. This lens has weathered the eventful years of revolution in cataract surgery technology and IOL designs from the era of the earliest lens designs to the present day (Figure 59-1).


The iris claw lens is a single-piece all-polymethylmethacrylate (PMMA) design. It is a plano-convex lens with 2 oval haptics that are split in the middle to form a pincer/claw-like mechanism, which the surgeon uses to fixate the lens to the iris tissue (Figure 59-2). The lens can be implanted horizontally, vertically, or obliquely to suit any clinical situation. The Artisan lens was also designed for use as a phakic IOL to correct high degrees of myopia and hypermetropia.


A modification of the classical Artisan design was made by Dr. Daljit Singh and was known as the Singh-Worst iris claw lens in late 1970s. This lens had round holes in the haptic and had the claw cut at an angle of 45 degrees toward the upper side rather than at 180 degrees unlike in the original design (Figure 59-3). This modification was made to facilitate implantation during the era of large-incision intra- and extracapsular surgery when viscoelastic agents were hard to come by and most cataract surgery and lens implantation was done under air.


Site of Fixation


The iris claw lens was originally designed to be fixated to the anterior surface of the iris. However, anteriorly fixated iris claw lens implantation has been shown to cause slow and persistent endothelial cell loss (Figure 59-4). Apart from this shortcoming, this lens has been well tolerated over a long period of time. Therefore, this lens has started being implanted to the posterior surface of the iris, totally avoiding the anterior chamber (Figure 59-5).


Indications for Iris Claw Lens Implantation


Inadequate or absent capsular support due to any reason and availability of iris support are the criteria for considering the iris claw lens for implantation. Among the indications for iris claw lens implantation are patients with congenital subluxated crystalline lenses, such as Marfan syndrome.1 Inadvertent posterior capsule rupture during phacoemulsification is another very important indication for iris claw lens implantation. This includes cases of posterior polar cataract.



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Figure 59-1. Plano-convex iris claw lens.




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Figure 59-2. Magnified view of claw mechanism.




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Figure 59-3. Stereo photograph of Singh-Worst iris claw lens implanted on the anterior surface of the iris more than 30 years ago.




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Figure 59-4. Anteriorly fixated iris claw lens.




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Figure 59-5. Retropupillary-fixated iris claw lens.






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Figure 59-7. Clayman forceps in profile.




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Figure 59-8. Magnified view of the tips of the right and left Clayman forceps.




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Figure 59-9. 27-gauge, 0.5-inch-long bent cannula for iris enclavation.


Additional patients benefiting from the iris claw lens include those with aphakia needing secondary lens implantation, including after vitreoretinal procedures, and those with a history of trauma.2,3


Eyes with severe zonular instability that cannot be addressed by capsular tension rings of different varieties can also receive the iris claw lens as a back-up. This lens works well in patients undergoing penetrating keratoplasty or endothelial keratoplasty for pseudophakic bullous keratopathy where the incriminating lens is exchanged for a retrofixated iris claw lens.4


No other lens except the iris claw lens can be used reliably in cases of extreme megalocornea5 or microcornea because this lens does not derive support from structures that vary with eyeball size.


Instruments Needed for Iris Claw IOL Implantation



  • A set of 2 Clayman forceps (right and left sided) to steady the iris claw lens inside the eye (Figures 59-6 through 59-8)
  • A bent 27-gauge cannula mounted on a 1-mL syringe to enclave/push the iris tissue through the claw of the iris claw lens (Figure 59-9)
  • 0.6-mm tri-facet diamond keratome for the paracenteses

Sizing the Iris Claw Lens


The overall dimensions of the original Worst lens manufactured by Ophtec BV, 8.5 mm length and 5 mm diameter, are much bigger than the lenses we currently use. The argument for a larger size of the lens was to achieve peripheral iris fixation and to avoid distorting the pupil. However, this brought the haptic of the lens perilously close to the periphery of the cornea and the endothelium. Perpetual iridodonesis and pseudophacodonesis led to intermittent endothelial touch and persistent cell loss. We found that if the lens is fixated to the iris tissue just outside the collarette, pupillary distortion does not occur, and this also does not impede the dilation of the pupil.



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Figure 59-10. Comparison of iris claw lens sizes.


The sizes of iris claw lenses we use in India are available in the following dimensions (Figures 59-10 and 59-11):



  • Size 1: Overall length 7.25 mm, 4.20-mm optic diameter
  • Size 2: Overall length 6.4 mm, 4.00-mm optic diameter
  • Size 3: Overall length 5.5 mm, 3.50-mm optic diameter
  • Size 4: Overall length 4.0 mm, 2.00-mm optic diameter

The only reason why these lenses can be implanted in small sizes is because this lens does not require the support of the external shell of the eyeball for its fixation.


IOL Power Calculation


IOL power calculation is performed using an A-constant of 115.5 for an anterior iris-fixated lens and 116.5 for a retropupillary-fixated lens.


Endothelial Cell Count


Surgeons should ensure that endothelial cell count is adequate before embarking upon iris claw lens implantation in complicated and compromised cases so that they know how much surgical trauma the eye can tolerate. The patient has to be counseled about the possibility of corneal decompensation in borderline cases. In our practice, we perform preoperative cell counts routinely and are comfortable with a minimum count of 1100 cells/mm2. Frank cases with pseudophakic bullous keratopathy are referred for a combined endothelial keratoplasty procedure.


For Beginners


A word of advice to beginners is that they must procure proper instruments before they venture to implant the iris claw lens. Second, they must rehearse the implantation technique in the wetlab many times over so that they get familiar with the properties of the IOL. Most important is to get a feel of the strength of the claw through which the iris tissue has to be enclaved and the amount of pressure and counterpressure required by each hand (Figure 59-12).



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Figure 59-11. Optic sizes and overall length of iris claw lenses.

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Jan 13, 2020 | Posted by in OPHTHALMOLOGY | Comments Off on Iris Claw IOL Fixation—Our Technique
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