- Email: [email protected]
Optimal folding axis for acrylic intraocular lenses
techniques
Optimal folding axis for acrylic intraocular lenses Kong T. Oh, MD, Kean T. Oh, MD ABSTRACT Acrylic intraocular lenses (IOLs) are easier to insert than foldable lenses of other materials. In addition to material properties, the structure of acrylic lenses allows an optimal folding angle along the 10 to 4 o'clock axis. Folding the IOL along this axis simplifies the manipulation of the leading haptic during insertion and places the trailing haptic within the capsular bag before the folded optic is released. J Cataract Refract Surg 1996; 22:667-670
T
he first acrylic intraocular lens (IOL) became commercially available in the United States in 1994. The optic is composed of acrylic, a foldable material with the highest refractive index of any 10L material, allowing for a thin optic with a wide optical zone. The lens has a 6.0 mm optic, an overall length of 13.0 mm, and poly(methyl methacrylate) haptics. Foldable acrylic lenses are inserted through a 3.5 mm incision after phacoemulsification using techniques similar to those used with silicone 10Ls. The structure and materials of acrylic 10Ls make implantation easier than with foldable lenses of other materials. We describe the optimal folding angle for acrylic 10Ls to facilitate their implantation.
Surgical Technique The lens is gripped with a tying forceps at the inferior optic- haptic junction and removed from the lens holder. Under the microscope, a smooth forceps is placed across the 10 to 4 o'clock axis on a dry 10L, extending over two thirds the diameter of the optic (Figure 1). The forceps gripping the 10L optic must be Reprint requests to Kong T Oh, MD, 8110 Market Street, Boardman, Ohio 44512.
perfectly smooth and clean because the optic surface may be marred by this maneuver if a toothed forceps is used. A Livernois-McDonald folder is used to fold the lens over the 10 to 4 o'clock axis by positioning the folding forceps over the internal ends of the haptics. The forceps' distal tip should be over the internal end of the trailing haptic, and the proximal bend of the forceps should be over the internal end of the leading haptic (Figure O. Because the acrylic lens is relatively rigid, downward pressure of the folding forceps with gentle counterpressure from the gripping smooth forceps will initiate folding. Once the optic begins to fold, the smooth forceps is disengaged. The McDonald forceps is used to complete the folding of the optic by gently releasing the grip tension exerted on the forceps (Figure O. The leading haptic is introduced into the corneal incision (Figure 2) and then compressed against the folded optic within the incision. A Colibri forceps provides counterpressure to the 10L as the lens passes through the incision (Figure 2). When the optic is in the anterior chamber, the folding forceps is rotated counterclockwise (Figure 2), placing the haptics in the capsular bag before the forceps are released. As the optic begins to unfold, a gentle tap over
J CATARACT REFRACT SURG-VOL 22, JULY/AUGUST 1996
667
TECHNIQUES: OH
Figure 1. (Oh) The lens is gripped with a tying forceps at the inferior optic-haptic junction; under the microscope, a smooth forceps is placed across the 10 to 4 o'clock axis (above left). A livernois-McDonald folder is used to fold the lens over the 10 to 4 o'clock axis (above right). As the optic begins to fold, the smooth forceps is disengaged and the McDonald forceps used to complete optic folding (below left and right).
the optic with the folding forceps ensures that the lens is within the capsular bag.
Discussion The first foldable IOLs were made of silicone. These lenses allowed surgeons to exploit the small incision through which phacoemulsification is performed. 1- 3 However, silicone lenses presented several technical challenges to the surgeon during their folding and insertion. Acrylic IOLs were developed to make these steps eaSIer. Currently, acrylic lenses are folded along the 12 to 6 o'clock axis according to the manufacturer's recommendations (Figure 3). However, inserting a lens folded in this manner leaves the trailing haptic outside the capsular bag when the optic unfolds, requiring the additional step of using a Sinskey hook to dial the trailing 668
loop into the capsular bag. The trailing loop also makes the optic difficult to control within the anterior chamber, increasing the risk of endothelial damage. N evertheless, this technique is useful in cases of posterior capsular rupture by limiting posterior deflection of the haptics. In uncomplicated cases, however, the technique proves cumbersome. 3 Folding the optic 90 degrees to this axis (along the 9 to 3 o'clock axis) obviates this additional step because the hap tics are placed in the capsular bag before the optic is unfolded2 ,3 (Figure 3). When a lens is folded in this manner, however, the leading haptic is difficult to manipulate during passage through a clear corneal incision. Rotating the IOL just before folding facilitates manipulation of the haptics during insertion. 3 When silicone lenses such as the SI-30NB are folded in this manner, "shoulders" at the optic-haptic junction that
J CATARACT REFRACT SURG-VOL 22, JULY/AUGUST 1996
TECHNIQUES: OH
Figure 2. (Oh) The leading haptic is introduced into the corneal incision and compressed against the folded optic within the incision (above left). A Colibri forceps provides counter pressure to the IOL as the lens passes through the incision (above right). When the optic is in the anterior chamber, the folding forceps is rotated counterclockwise (below left). As the optic begins to unfold, gently tapping the folding forceps ensures the lens is within the capsular bag (below right).
Figure 3. (Oh) Demonstration of folding the acrylic lens along the 9 to 3 o'clock axis (right, above and below). Folding the lens along the 10 to 4 axis (middle, above and below). Folding the lens along the 12 to 6 o'clock axis (left, above and below). J CATARACT REFRACT SURG-VOL 22, JULY/AUGUST 1996
669
TECHNIQUES: OH
extend beyond the smooth edge are formed by the folded optic and may catch as the lens passes through the incision. This deflects the haptic posteriorly, placing the posterior capsule at risk of puncture by the leading haptic. Acrylic lenses with a smooth optic- haptic junction allow surgeons to take advantage of the optimal folding angle for IOLs with minimal risk of posterior capsular perforation. Not all surgeons who have used acrylic lenses believe that this optic material facilitates IOL insertion. One of us (Kong Oh) has inserted more than 3000 silicone and 300 acrylic lenses and found that switching from silicone to acrylic lenses at first seemed awkward. With experience, however, we believe that surgeons will appreciate the greater control during insertion afforded by the slower opening optic and the optichaptic junction. Ultimately, the decision on what type of lens to use is based on surgeon preference and training.
670
In conclusion, when acrylic lenses are folded along the 10 to 4 o'clock axis, the haptics are easier to manage during insertion and are positioned within the capsular bag before the folded optic is released, providing advantages for the surgeon over the two commonly used techniques.
References 1. Davison JA. Modified insertion technique for SI-18NB
intraocular lens.
J Cataract Refract Surg 1991; 17:849-
853 2. Oh KT, Oh KT. Simplified insertion technique for the SI-26NB foldable intraocular lens. J Cataract Refract Surg 1992; 18:619-622 3. Fine IH. Response. In: Masket S, ed, Consultation section. J Cataract Refract Surg 1992; 18:207-208
] CATARACT REFRACT SURG-VOL 22,]ULY/AUGUST 1996
Optimal folding axis for acrylic intraocular lenses Kong T. Oh, MD, Kean T. Oh, MD ABSTRACT Acrylic intraocular lenses (IOLs) are easier to insert than foldable lenses of other materials. In addition to material properties, the structure of acrylic lenses allows an optimal folding angle along the 10 to 4 o'clock axis. Folding the IOL along this axis simplifies the manipulation of the leading haptic during insertion and places the trailing haptic within the capsular bag before the folded optic is released. J Cataract Refract Surg 1996; 22:667-670
T
he first acrylic intraocular lens (IOL) became commercially available in the United States in 1994. The optic is composed of acrylic, a foldable material with the highest refractive index of any 10L material, allowing for a thin optic with a wide optical zone. The lens has a 6.0 mm optic, an overall length of 13.0 mm, and poly(methyl methacrylate) haptics. Foldable acrylic lenses are inserted through a 3.5 mm incision after phacoemulsification using techniques similar to those used with silicone 10Ls. The structure and materials of acrylic 10Ls make implantation easier than with foldable lenses of other materials. We describe the optimal folding angle for acrylic 10Ls to facilitate their implantation.
Surgical Technique The lens is gripped with a tying forceps at the inferior optic- haptic junction and removed from the lens holder. Under the microscope, a smooth forceps is placed across the 10 to 4 o'clock axis on a dry 10L, extending over two thirds the diameter of the optic (Figure 1). The forceps gripping the 10L optic must be Reprint requests to Kong T Oh, MD, 8110 Market Street, Boardman, Ohio 44512.
perfectly smooth and clean because the optic surface may be marred by this maneuver if a toothed forceps is used. A Livernois-McDonald folder is used to fold the lens over the 10 to 4 o'clock axis by positioning the folding forceps over the internal ends of the haptics. The forceps' distal tip should be over the internal end of the trailing haptic, and the proximal bend of the forceps should be over the internal end of the leading haptic (Figure O. Because the acrylic lens is relatively rigid, downward pressure of the folding forceps with gentle counterpressure from the gripping smooth forceps will initiate folding. Once the optic begins to fold, the smooth forceps is disengaged. The McDonald forceps is used to complete the folding of the optic by gently releasing the grip tension exerted on the forceps (Figure O. The leading haptic is introduced into the corneal incision (Figure 2) and then compressed against the folded optic within the incision. A Colibri forceps provides counterpressure to the 10L as the lens passes through the incision (Figure 2). When the optic is in the anterior chamber, the folding forceps is rotated counterclockwise (Figure 2), placing the haptics in the capsular bag before the forceps are released. As the optic begins to unfold, a gentle tap over
J CATARACT REFRACT SURG-VOL 22, JULY/AUGUST 1996
667
TECHNIQUES: OH
Figure 1. (Oh) The lens is gripped with a tying forceps at the inferior optic-haptic junction; under the microscope, a smooth forceps is placed across the 10 to 4 o'clock axis (above left). A livernois-McDonald folder is used to fold the lens over the 10 to 4 o'clock axis (above right). As the optic begins to fold, the smooth forceps is disengaged and the McDonald forceps used to complete optic folding (below left and right).
the optic with the folding forceps ensures that the lens is within the capsular bag.
Discussion The first foldable IOLs were made of silicone. These lenses allowed surgeons to exploit the small incision through which phacoemulsification is performed. 1- 3 However, silicone lenses presented several technical challenges to the surgeon during their folding and insertion. Acrylic IOLs were developed to make these steps eaSIer. Currently, acrylic lenses are folded along the 12 to 6 o'clock axis according to the manufacturer's recommendations (Figure 3). However, inserting a lens folded in this manner leaves the trailing haptic outside the capsular bag when the optic unfolds, requiring the additional step of using a Sinskey hook to dial the trailing 668
loop into the capsular bag. The trailing loop also makes the optic difficult to control within the anterior chamber, increasing the risk of endothelial damage. N evertheless, this technique is useful in cases of posterior capsular rupture by limiting posterior deflection of the haptics. In uncomplicated cases, however, the technique proves cumbersome. 3 Folding the optic 90 degrees to this axis (along the 9 to 3 o'clock axis) obviates this additional step because the hap tics are placed in the capsular bag before the optic is unfolded2 ,3 (Figure 3). When a lens is folded in this manner, however, the leading haptic is difficult to manipulate during passage through a clear corneal incision. Rotating the IOL just before folding facilitates manipulation of the haptics during insertion. 3 When silicone lenses such as the SI-30NB are folded in this manner, "shoulders" at the optic-haptic junction that
J CATARACT REFRACT SURG-VOL 22, JULY/AUGUST 1996
TECHNIQUES: OH
Figure 2. (Oh) The leading haptic is introduced into the corneal incision and compressed against the folded optic within the incision (above left). A Colibri forceps provides counter pressure to the IOL as the lens passes through the incision (above right). When the optic is in the anterior chamber, the folding forceps is rotated counterclockwise (below left). As the optic begins to unfold, gently tapping the folding forceps ensures the lens is within the capsular bag (below right).
Figure 3. (Oh) Demonstration of folding the acrylic lens along the 9 to 3 o'clock axis (right, above and below). Folding the lens along the 10 to 4 axis (middle, above and below). Folding the lens along the 12 to 6 o'clock axis (left, above and below). J CATARACT REFRACT SURG-VOL 22, JULY/AUGUST 1996
669
TECHNIQUES: OH
extend beyond the smooth edge are formed by the folded optic and may catch as the lens passes through the incision. This deflects the haptic posteriorly, placing the posterior capsule at risk of puncture by the leading haptic. Acrylic lenses with a smooth optic- haptic junction allow surgeons to take advantage of the optimal folding angle for IOLs with minimal risk of posterior capsular perforation. Not all surgeons who have used acrylic lenses believe that this optic material facilitates IOL insertion. One of us (Kong Oh) has inserted more than 3000 silicone and 300 acrylic lenses and found that switching from silicone to acrylic lenses at first seemed awkward. With experience, however, we believe that surgeons will appreciate the greater control during insertion afforded by the slower opening optic and the optichaptic junction. Ultimately, the decision on what type of lens to use is based on surgeon preference and training.
670
In conclusion, when acrylic lenses are folded along the 10 to 4 o'clock axis, the haptics are easier to manage during insertion and are positioned within the capsular bag before the folded optic is released, providing advantages for the surgeon over the two commonly used techniques.
References 1. Davison JA. Modified insertion technique for SI-18NB
intraocular lens.
J Cataract Refract Surg 1991; 17:849-
853 2. Oh KT, Oh KT. Simplified insertion technique for the SI-26NB foldable intraocular lens. J Cataract Refract Surg 1992; 18:619-622 3. Fine IH. Response. In: Masket S, ed, Consultation section. J Cataract Refract Surg 1992; 18:207-208
] CATARACT REFRACT SURG-VOL 22,]ULY/AUGUST 1996