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New caliper for small incision cataract surgery
New caliper for small incision cataract surgery Thomas Kohnen, MD ABSTRACT In cataract surgery, incision size determines various factors such as wound stability, corneal curvature changes, postoperative induced astigmatism, and visual rehabilitation. A mechanical caliper has been developed for experimental and clinical studies of incision sizes ranging between 1.0 and 6.0 mm. The caliper has a screw that allows measurements in 0.1 mm steps. The device is produced for two ranges: 2.0 to 4.0 mm and 1.0 to 6.0 mm. The precision of 0.1 mm was confirmed with a vernier caliper in a cadaver eye study. Unlike gauges that determine incision size by trial and error and a combined system of internal and vernier calipers, only one measurement is necessary with this caliper. J Cataract Refract Surg 1997; 23:1298-1300
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ncision size is an important factor in wound stability, astigmatic change, and visual outcome after cataract surgery. The advent of phacoemulsification and foldable intraocular lens (IOL) implantation has increased the use of small incisions. Recent research has shown that tight cataract wounds are irreversibly enlarged during phacoemulsification and foldable IOL implantation. l -4 Therefore, postoperative measurements of incision size are recommended when reporting and studying induced astigmatism or corneal topographic
From the Cullen Eye Imtitute. Baylor College ofMdicine. Department of Ophthalmology, Houston, Texas, USA, and the Johann Wolfgang Goethe-University, Department ofOphthalmology, Frankfort am Main, Germany.
shape changes after small incision cataract surgery.3,4 To measure incision sizes in clinical and experimental settings, a new mechanical caliper was developed.
Design The metal caliper (Geuder GmbH) has two arms with fine tips (Figure 1). The length and angulation of the tips allow external and internal measurements of tunnel incisions. A screw connects the two arms of the caliper in the middle of the device (Figure 2). The instrument measures distances from 1.0 to 6.0 mm in 0.1 mm steps. The device is produced for two ranges: 2.0 to 4.0 mm and 1.0 to 6.0 mm (Figures 2 and 3). The thread of the screw is covered with a layer of silicone so the screw does not move after the measurement.
Supported in part by a Deutsche Forschungrgemeimchaft Postdoctoral &search Grant DFG-Ko 159511-1 and 1-2 and an unrestricted grant from Research to Prevent Blindness, New York, New York, USA. The author has no proprietary interest in the product mentioned. Hartmut Fath. Geuder GmbH, Heidelberg, Germany, helped with the design of the small incision caliper. Reprint requests to Thomas Kohnen, MD, Johann Wolfgang GoetheUniversity, Department ofOphthalmology, Theodor-Stern-Kai 7, 60590 Frankfort am Main, Germany. 1298
Discussion In recent clinical studies, the incision size of cataract wounds was measured with several devices. Steinert and Deacon 1 used incision gauges to verify incision size. In most cases, these gauges require several measurements and can enlarge the wound slightly. Mackool and RusselF used an Osher internal caliper whose accuracy
J CATARACT REFRACT SURG-VOL 23, NOVEMBER 1997
TECHNIQUES: KOHNEN
Figure 2. (Kohnen) Design specifications of the caliper screw (range 1.0 to 6.0 mm).
Figure 1. (Kohnen) The caliper for small incision cataract surgery can be sterilized, is suitable for intraoperative use, and is available in two ranges.
had been verified against a standard millimeter ruler. This caliper has an incremental scale of 0.5 mm and therefore requires some estimation of the measurement on the part of the observer. In an experimental study, modified Osher and vernier calipers were used to study the incision dimensions with an accuracy of 0.0 1 mm. 3,4
o Figure 3. (Kohnen) Sketch of the small incision caliper screw (range 2.0 to 4.0 mm) shows the 0.1 mm measurement steps. The arrows indicate the motion of the screw. In this position, the caliper would measure an incision size of 3.5 mm.
This modified Osher caliper also measures with an accuracy of 0.5 mm steps and therefore requires a vernier caliper for more precise values. This method is too time consuming for clinical studies; therefore, the new device was developed. The practicability of the new caliper was evaluated in a study of forceps and injector implantation of threepiece, high-refractive-index silicone IOLs.s The measurements were first performed with the modified Osher and vernier calipers4 and then repeated with the new device. An accuracy of 0.1 mm was found. An advantage of this device over incision gauges! and the modified Osher caliper/vernier caliper system4 is that only one maneuver is necessary to determine incision size. With the appropriate surgical experience, incision enlargement can be avoided. However, only an optically driven measuring device can eliminate contact of ocular tissue by the forceps tip, which might enlarge the tunnel dimensions slightly. For currently used small incision cataract techniques and available foldable IOLs,4 the new caliper with a measurement range of 2.0 to 4.0 mm (Figure 3) should be used. In summary, the small incision caliper allows easy, atraumatic intraoperative measurement of incision sizes for small incision surgery with an accuracy of 0.1 mm.
References
J. Enlargement of incision width during phacoemulsification and folded intraocular lens implant surgery. Ophthalmology 1996; 103:220-225
1. Steinert RF, Deacon
J CATARACT REFRACT SURG-VOL 23, NOVEMBER 1997
1299
TECHNIQUES: KOHNEN
2. Mackool RJ, Russell RS. Effect of foldable intraocular lens insertion on incision width. J Cataract Refract Surg 1996; 22:571-574 3. Kohnen T, Lambert RJ, Koch DD. InzisionsgroBen fur faltbare Intraokularlinsen. In: Vorosmarthy D, Duncker G, Hartmann C, eds, 10. KongreB der Deutschsprachigen Gesellschaft ftir Intraokularlinsen-Implantation und
1300
refraktive Chirurgie, Budapest 1996. Berlin, Heidelberg, Springer, 1997; 79-84 4. Kohnen T, Lambert JR, Koch DD. Incision sizes for foldable intraocular lenses. Ophthalmology 1997; 104: 1277-1286 5. Kohnen T. Vergleichende Untersuchung zur InzisionsgroBe von Intraokularlinsen aus hochrefraktivem Silikon (abstract). Ophthalmologe 1997; 95:S61
J CATARACT REFRACT SURG-VOL 23, NOVEMBER 1997
I
ncision size is an important factor in wound stability, astigmatic change, and visual outcome after cataract surgery. The advent of phacoemulsification and foldable intraocular lens (IOL) implantation has increased the use of small incisions. Recent research has shown that tight cataract wounds are irreversibly enlarged during phacoemulsification and foldable IOL implantation. l -4 Therefore, postoperative measurements of incision size are recommended when reporting and studying induced astigmatism or corneal topographic
From the Cullen Eye Imtitute. Baylor College ofMdicine. Department of Ophthalmology, Houston, Texas, USA, and the Johann Wolfgang Goethe-University, Department ofOphthalmology, Frankfort am Main, Germany.
shape changes after small incision cataract surgery.3,4 To measure incision sizes in clinical and experimental settings, a new mechanical caliper was developed.
Design The metal caliper (Geuder GmbH) has two arms with fine tips (Figure 1). The length and angulation of the tips allow external and internal measurements of tunnel incisions. A screw connects the two arms of the caliper in the middle of the device (Figure 2). The instrument measures distances from 1.0 to 6.0 mm in 0.1 mm steps. The device is produced for two ranges: 2.0 to 4.0 mm and 1.0 to 6.0 mm (Figures 2 and 3). The thread of the screw is covered with a layer of silicone so the screw does not move after the measurement.
Supported in part by a Deutsche Forschungrgemeimchaft Postdoctoral &search Grant DFG-Ko 159511-1 and 1-2 and an unrestricted grant from Research to Prevent Blindness, New York, New York, USA. The author has no proprietary interest in the product mentioned. Hartmut Fath. Geuder GmbH, Heidelberg, Germany, helped with the design of the small incision caliper. Reprint requests to Thomas Kohnen, MD, Johann Wolfgang GoetheUniversity, Department ofOphthalmology, Theodor-Stern-Kai 7, 60590 Frankfort am Main, Germany. 1298
Discussion In recent clinical studies, the incision size of cataract wounds was measured with several devices. Steinert and Deacon 1 used incision gauges to verify incision size. In most cases, these gauges require several measurements and can enlarge the wound slightly. Mackool and RusselF used an Osher internal caliper whose accuracy
J CATARACT REFRACT SURG-VOL 23, NOVEMBER 1997
TECHNIQUES: KOHNEN
Figure 2. (Kohnen) Design specifications of the caliper screw (range 1.0 to 6.0 mm).
Figure 1. (Kohnen) The caliper for small incision cataract surgery can be sterilized, is suitable for intraoperative use, and is available in two ranges.
had been verified against a standard millimeter ruler. This caliper has an incremental scale of 0.5 mm and therefore requires some estimation of the measurement on the part of the observer. In an experimental study, modified Osher and vernier calipers were used to study the incision dimensions with an accuracy of 0.0 1 mm. 3,4
o Figure 3. (Kohnen) Sketch of the small incision caliper screw (range 2.0 to 4.0 mm) shows the 0.1 mm measurement steps. The arrows indicate the motion of the screw. In this position, the caliper would measure an incision size of 3.5 mm.
This modified Osher caliper also measures with an accuracy of 0.5 mm steps and therefore requires a vernier caliper for more precise values. This method is too time consuming for clinical studies; therefore, the new device was developed. The practicability of the new caliper was evaluated in a study of forceps and injector implantation of threepiece, high-refractive-index silicone IOLs.s The measurements were first performed with the modified Osher and vernier calipers4 and then repeated with the new device. An accuracy of 0.1 mm was found. An advantage of this device over incision gauges! and the modified Osher caliper/vernier caliper system4 is that only one maneuver is necessary to determine incision size. With the appropriate surgical experience, incision enlargement can be avoided. However, only an optically driven measuring device can eliminate contact of ocular tissue by the forceps tip, which might enlarge the tunnel dimensions slightly. For currently used small incision cataract techniques and available foldable IOLs,4 the new caliper with a measurement range of 2.0 to 4.0 mm (Figure 3) should be used. In summary, the small incision caliper allows easy, atraumatic intraoperative measurement of incision sizes for small incision surgery with an accuracy of 0.1 mm.
References
J. Enlargement of incision width during phacoemulsification and folded intraocular lens implant surgery. Ophthalmology 1996; 103:220-225
1. Steinert RF, Deacon
J CATARACT REFRACT SURG-VOL 23, NOVEMBER 1997
1299
TECHNIQUES: KOHNEN
2. Mackool RJ, Russell RS. Effect of foldable intraocular lens insertion on incision width. J Cataract Refract Surg 1996; 22:571-574 3. Kohnen T, Lambert RJ, Koch DD. InzisionsgroBen fur faltbare Intraokularlinsen. In: Vorosmarthy D, Duncker G, Hartmann C, eds, 10. KongreB der Deutschsprachigen Gesellschaft ftir Intraokularlinsen-Implantation und
1300
refraktive Chirurgie, Budapest 1996. Berlin, Heidelberg, Springer, 1997; 79-84 4. Kohnen T, Lambert JR, Koch DD. Incision sizes for foldable intraocular lenses. Ophthalmology 1997; 104: 1277-1286 5. Kohnen T. Vergleichende Untersuchung zur InzisionsgroBe von Intraokularlinsen aus hochrefraktivem Silikon (abstract). Ophthalmologe 1997; 95:S61
J CATARACT REFRACT SURG-VOL 23, NOVEMBER 1997