Posterior Chamber Phakic Intraocular Lens





Introduction


In 1986, Fyodorov originated the first plate posterior chamber phakic intraocular lens (PIOL). He used a one-piece silicone collar button PIOL with a Teflon coat. Encouraging initial results were achieved but problems with cataract formation, uveitis, glaucoma, and decentration led to changes in lens design and type of material to improve biocompatibility.


Currently, there are three phakic posterior chamber lenses. Two are available: the implantable contact lens (ICL; manufactured by STAAR Surgical) and the phakic refractive lens (PRL; manufactured by CIBA). One is under evaluation: the Sticklens, developed by IOLTECH.




Lens Design


The STAAR surgical ICL is made of a collagen copolymer, a compound combining acrylic and porcine collagen (less than 0.1% collagen). Its refractive index is 1.45 at 35°C. The polymer material is soft, elastic, and hydrophilic. The optical zone of myopic lenses is 60 µm thick; the diameter varies between 4.5 and 5.5 mm according to the power required. The optical zone diameter of hyperopic lenses is 5.5 mm. Available powers are −3 to −23 diopters (D) for myopic lenses, and +3 D to +21.5 D for hyperopic lenses. Several lengths are manufactured: 11 to 13.0 mm for hyperopic lenses, and 11.5 to 13.5 mm for myopic lenses. An astigmatic ICL is also available, but it was marketed too recently to appear in articles in peer-reviewed journals. This implant is placed in the ciliary sulcus. The posterior surface is concave in order to vault over the anterior capsule.


The CIBA PRL is made from an ultra-thin silicon polymer; its refractive index is 1.46. The material is soft, elastic, and hydrophobic. The width is 6.0 mm; two lengths are available for myopic lenses: 10.8 or 11.3 mm, and one for hyperopic lenses: 10.6 mm. Available powers are −3 to −20 for myopic lenses, and +3 to +15 for hyperopic lenses.


The lens has no anatomic fixation sites; it is supposed to move unaided into a centered position inside the posterior chamber spaces, without exerting pressure on the ciliary structures, the zonule in particular; it does not come into contact with the anterior capsule of the crystalline lens: it “floats.”


The Sticklens, developed by IOLTECH, is made of a high-hydrophilic material in order to allow metabolic exchanges through the implant; it is “stuck” on the anterior capsule of the crystalline lens.




Preoperative Evaluation


Exclusion criteria include previous intraocular surgery, endothelial dystrophy, opacities of the crystalline lens, glaucoma, pigment dispersion syndrome, diabetic retinopathy and systemic disease, nonstable ametropia, and an anterior chamber depth less than 2.8 mm in myopic eyes and 3.00 mm in hyperopic eyes.


Lens power calculation is performed with formulae that take several variables into account: manifest and cycloplegic refraction, keratometric power, anterior chamber depth, and corneal thickness.


The length of the lens is determined based on the horizontal corneal diameter. White-to-white measurement can be made by several methods: caliper, gauge, videokeratoscope, photographic devices, and ultrasound biometry (UBM). However, only very expensive devices, such as high-frequency UBM, could give an accurate measurement of the sulcus diameter. The size of the PIOL chosen is, in most cases, white-to-white length plus 0.5 mm, rounded to the nearest 0.5 mm increment for myopic eyes, and white-to-white length for hyperopic eyes.




Surgical Technique ( )


Two weeks before surgery, laser iridotomies are performed. Two peripheral superior iridotomies are placed 80 degrees apart in order to avoid the possibility of iridotomy occlusion by the haptics of the implant. Otherwise, a surgical iridectomy will be performed at the time of implantation.


Preparation and Anesthesia


A combination of mydriatic topical medications is applied serially, beginning 1 hour before surgery. The anesthesia methods—general anesthesia, peribulbar injection, or topical anesthesia—are based on patient and surgeon preference.


Surgical Procedure


A puncture is performed and aqueous humor is replaced by a viscoelastic gel. A temporal corneal tunnel (width 3.2 mm, length 1.75–2 mm) is created. A narrow diamond blade allows progressive opening of the anterior chamber. Viscoelastic (ideally, methylcellulose) is injected into the anterior chamber. The implant can be inserted by different techniques.


Inserting the Implant With an Injector ( Fig. 31.1 )


The IOL is positioned in the lens insertion cartridge under direct vision through the operating microscope. In the absence of a soft-tip injector, a small silicon sponge can be placed to protect the IOL from the hard injector arm.




Fig. 31.1


Injectors for the STAAR surgical implantable contact lens.


Because IOL insertion into the cartridge is complicated and time-consuming, it must be done before the incision is made.


The injector tip is placed in the tunnel and the lens is injected into the anterior chamber. As the IOL unfolds slowly, its progression can be controlled, to ensure proper orientation.


Inserting the Implant With Forceps ( Fig. 31.2 )


The IOL is easy to fold between the jaws of a MacPherson forceps. The tip of the forceps is introduced in the entrance of the tunnel. Then, another MacPherson forceps, held in the operator’s other hand, is used to grasp the sides of the implant. The first forceps is opened, regrasps the IOL a little further, and pushes it slowly. By repeating these maneuvers with the forceps, the operator moves the IOL into the tunnel, and the IOL unfolds in a controlled manner. The tip of the forceps must never enter into the anterior chamber to avoid contact with the crystalline lens.




Fig. 31.2


Intraoperative sequential views of implantation of the STAAR surgical implantable contact lens using the forceps technique. (A) Lens folding. (B) Lens insertion. (C) Trailing haptic insertion. (D) Positioning of distal haptic. (E) Positioning of proximal haptic.










As the IOL unfolds, its proper orientation must be checked. Then, each foot plate is placed one after the other beneath the iris with a specially designed, flat, nonpolished manipulator, without pressure being placed on the crystalline lens. It is important to avoid touching the optic of a myopic lens in the middle, as it is the thinnest part. Then, the viscoelastic is removed with gentle irrigation–aspiration and acetylcholine chloride is injected.


A Dementiev forceps can be used to implant a PRL; the implant is grasped by the special forceps designed to prevent damages on the optical zone (only the haptic area of the implant is in contact with the forceps). The forceps is pushed into the middle part of the anterior chamber. The forceps is opened gently to release the lens; care must be taken because the lens can be damaged when withdrawing the forceps.




Preparation and Anesthesia


A combination of mydriatic topical medications is applied serially, beginning 1 hour before surgery. The anesthesia methods—general anesthesia, peribulbar injection, or topical anesthesia—are based on patient and surgeon preference.




Surgical Procedure


A puncture is performed and aqueous humor is replaced by a viscoelastic gel. A temporal corneal tunnel (width 3.2 mm, length 1.75–2 mm) is created. A narrow diamond blade allows progressive opening of the anterior chamber. Viscoelastic (ideally, methylcellulose) is injected into the anterior chamber. The implant can be inserted by different techniques.


Inserting the Implant With an Injector ( Fig. 31.1 )


The IOL is positioned in the lens insertion cartridge under direct vision through the operating microscope. In the absence of a soft-tip injector, a small silicon sponge can be placed to protect the IOL from the hard injector arm.




Fig. 31.1


Injectors for the STAAR surgical implantable contact lens.


Because IOL insertion into the cartridge is complicated and time-consuming, it must be done before the incision is made.


The injector tip is placed in the tunnel and the lens is injected into the anterior chamber. As the IOL unfolds slowly, its progression can be controlled, to ensure proper orientation.


Inserting the Implant With Forceps ( Fig. 31.2 )


The IOL is easy to fold between the jaws of a MacPherson forceps. The tip of the forceps is introduced in the entrance of the tunnel. Then, another MacPherson forceps, held in the operator’s other hand, is used to grasp the sides of the implant. The first forceps is opened, regrasps the IOL a little further, and pushes it slowly. By repeating these maneuvers with the forceps, the operator moves the IOL into the tunnel, and the IOL unfolds in a controlled manner. The tip of the forceps must never enter into the anterior chamber to avoid contact with the crystalline lens.




Fig. 31.2


Intraoperative sequential views of implantation of the STAAR surgical implantable contact lens using the forceps technique. (A) Lens folding. (B) Lens insertion. (C) Trailing haptic insertion. (D) Positioning of distal haptic. (E) Positioning of proximal haptic.










As the IOL unfolds, its proper orientation must be checked. Then, each foot plate is placed one after the other beneath the iris with a specially designed, flat, nonpolished manipulator, without pressure being placed on the crystalline lens. It is important to avoid touching the optic of a myopic lens in the middle, as it is the thinnest part. Then, the viscoelastic is removed with gentle irrigation–aspiration and acetylcholine chloride is injected.


A Dementiev forceps can be used to implant a PRL; the implant is grasped by the special forceps designed to prevent damages on the optical zone (only the haptic area of the implant is in contact with the forceps). The forceps is pushed into the middle part of the anterior chamber. The forceps is opened gently to release the lens; care must be taken because the lens can be damaged when withdrawing the forceps.




Inserting the Implant With an Injector ( Fig. 31.1 )


The IOL is positioned in the lens insertion cartridge under direct vision through the operating microscope. In the absence of a soft-tip injector, a small silicon sponge can be placed to protect the IOL from the hard injector arm.




Fig. 31.1


Injectors for the STAAR surgical implantable contact lens.


Because IOL insertion into the cartridge is complicated and time-consuming, it must be done before the incision is made.


The injector tip is placed in the tunnel and the lens is injected into the anterior chamber. As the IOL unfolds slowly, its progression can be controlled, to ensure proper orientation.




Inserting the Implant With Forceps ( Fig. 31.2 )


The IOL is easy to fold between the jaws of a MacPherson forceps. The tip of the forceps is introduced in the entrance of the tunnel. Then, another MacPherson forceps, held in the operator’s other hand, is used to grasp the sides of the implant. The first forceps is opened, regrasps the IOL a little further, and pushes it slowly. By repeating these maneuvers with the forceps, the operator moves the IOL into the tunnel, and the IOL unfolds in a controlled manner. The tip of the forceps must never enter into the anterior chamber to avoid contact with the crystalline lens.




Fig. 31.2


Intraoperative sequential views of implantation of the STAAR surgical implantable contact lens using the forceps technique. (A) Lens folding. (B) Lens insertion. (C) Trailing haptic insertion. (D) Positioning of distal haptic. (E) Positioning of proximal haptic.










As the IOL unfolds, its proper orientation must be checked. Then, each foot plate is placed one after the other beneath the iris with a specially designed, flat, nonpolished manipulator, without pressure being placed on the crystalline lens. It is important to avoid touching the optic of a myopic lens in the middle, as it is the thinnest part. Then, the viscoelastic is removed with gentle irrigation–aspiration and acetylcholine chloride is injected.


A Dementiev forceps can be used to implant a PRL; the implant is grasped by the special forceps designed to prevent damages on the optical zone (only the haptic area of the implant is in contact with the forceps). The forceps is pushed into the middle part of the anterior chamber. The forceps is opened gently to release the lens; care must be taken because the lens can be damaged when withdrawing the forceps.




Functional Results


Most of the published results concern series of patients implanted with an ICL. Only two publications present results obtained by PRL implantation.


Predictability


Predictability was good and results were relatively similar in all studies, as shown in the following publications.


Assetto et al. implanted 15 lenses in 14 patients. Average follow-up was 7 ± 1.95 months. Mean spherical equivalent was −15.3 D ± 3.1 D preoperatively, −2 D ± 1.5 D postoperatively. Only 31% of eyes had less than 1 D of residual myopia. However, an old model of lenses was used.


Rosen and Gore operated on 16 myopic eyes (−5.25 D to −14.50 D). At 3 months after surgery, refraction ranged from −1.25 D to +1 D; 56.2% of eyes were within 0.50 D from emmetropia.


Zaldivar et al. analyzed a cohort of 124 eyes; the mean follow-up period was 11 months (range, 1–36 months). The mean preoperative spherical equivalent was −13.38 ± 2.23 D (range, −8.50 D to −18.63 D). The target was emmetropia. The postoperative mean spherical equivalent was −0.78 D ± 0.87 D (range, +1.63 D to −3.50 D); 69% of the eyes were within 1 D and 44% within 0.50 D from emmetropia.


Arné and Lesueur implanted 58 eyes of 46 myopic patients. Follow-up ranged from 9 months to 2 years. Spherical equivalent was −13.85 D ± 4.61 D (range, −8 D to −19.21 D) preoperatively and −1.22 D ± 0.58 D postoperatively; 56.9 % of the eyes were within 1 D of emmetropia. Residual myopia was more than 2 D in 15.5% of the eyes.


Uusitalo et al. reported the results of ICL implantation in 38 eyes of 22 patients. The mean preoperative myopia was −15.10 D (range, −7.75 D to 29 D); the mean follow-up was 13.6 months (range, 6–24 months). Postoperatively, the mean spherical equivalent refraction was −2 D ± 2.48 D (range, +0.13 D to −13 D); 96.4% of the eyes were within 1 D and 85.7% within 0.5 D of emmetropia.


Pallikaris et al. evaluated the 1-year results of PRL implantation in 34 myopic eyes. They found a statistically significant reduction in the manifest refraction in spherical equivalent (preoperative: −14.70 D, range, −10.5 D to −20.75 D; postoperative: −0.61 D, range, −2.25 D to +1 D); 79% and 44% of the eyes were within 1 D and 0.5 D of target refraction, respectively.


Sanders et al. reported on 526 eyes with between 3.0 D and 20.0 D of myopia participating in the US Food and Drug Administration clinical trial of the ICL for myopia: 67.5% of patients were within 0.5 D and 88.2% were within 1.0 D of predicted refraction.


There were few studies on results of hyperopic ICL : Rosen and Gore operated on 9 hyperopic eyes (preoperative spherical equivalent [SE] range, +2.25 D to +5.62 D); 3 months postoperatively, refraction ranged from −0.12 D to +1 D.


Davidorf et al. implanted a collamer PIOL into 24 eyes with hyperopia greater than 3.50 D. The mean preoperative SE was +6.51 D ± 2.08 D (range, +3.75 D to +10.50 D). The mean postoperative SE was −0.39 D ± 1.29 D (range, +1.25 D to −3.88 D). Postoperatively, 79% of the eyes were within +1 D and 58% within +0.50 D from emmetropia. These results compare favorably with predicted results of the authors’ series of highly myopic eyes.


Gimbel and Ziémba reported one case of an astigmatic eye implanted with a posterior chamber PIOL. Manifest preoperative refraction was −9.25 (−2.25 × 98 degrees); 5 months after surgery, manifest refraction was +0.25 (−0.25 × 60 degrees).


Hoyos et al. presented the results of implantation of a PRL in 31 eyes (17 myopic, 14 hyperopic). The mean preoperative spherical equivalent was −18.46 D (range, −11.85 D to −26 D) for myopia, +7.77 D (range, +5.25 D to 11 D) for hyperopia. At 1 year, the mean postoperative spherical equivalent in the myopic group was −0.22 D (range, +1.50 to −2 D) and −0.38 (range +1.50 to −1.75 D).


Visual Acuity


In the series of phakic implantation in myopic eyes by Zaldivar et al., the preoperative best-corrected visual acuity (BCVA) was 20/40 or better in 80% and 20/20 or better in 5% of the eyes. Postoperatively, uncorrected visual acuity (UCVA) was 20/40 or better in 93% and 20/20 or better in 19% of the eyes.


Again, two or more lines of corrected visual acuity was attained in 36% of the cases; 7% of the eyes lost one line, 0.8% lost 2 lines.


In the series reported by Arné and Lesueur, the mean preoperative BCVA was 0.57 and the mean postoperative UCVA and BCVA were 0.40 and 0.71, respectively. The postoperative UCVA was better than the preoperative BCVA in 15.5% of the cases, unchanged in 15.5%, and worse in 68.9% of the eyes. The mean efficacy index (ratio of postoperative UCVA to preoperative BCVA) was 0.84. A total of 20.6% of the eyes retained the same BCVA, 77% gained one or more lines, and 3.4% lost two lines. Safety, calculated as the ratio between postoperative and preoperative BCVA, was 1.46.


In the series reported by Uusitalo et al., the BCVA improved by one or more lines in 71.9% of the eyes; 6.3% of the eyes lost one line of BCVA.


Pallikaris et al., after implantation of PRLs in myopic eyes, noted an improvement of BCVA from 0.70 ± 0.24 to 0.85 ± 0.24.


In the series of myopic and hyperopic patients implanted with PRL by Hoyos et al., lines of BCVA were gained in 65% of the myopic eyes, with eight eyes gaining one line and three eyes gaining two lines. No eye lost one line of BCVA. In the hyperopic group, one eye gained one line of BCVA and one eye lost one line.


Good efficacy and predictability have been demonstrated in all studies on posterior chamber phakic lenses for treatment of high myopias. The marked gains in postoperative BCVA compared with the preoperative spectacle BCVA in high myopes are largely due to elimination of the spectacle-induced image reduction.


Conversely, only 8% of the hyperopic eyes operated on by Davidorf et al. demonstrated a gain in postoperative BCVA compared to the preoperative spectacle BCVA. In this series, 7 of 24 eyes (29%) lost one or more lines of postoperative spectacle BCVA. This is explained by the loss of magnification induced by the surgery. Also, 4% of the eyes lost two or more lines of spectacle BCVA due to postoperative glaucoma.


Stability


Excellent stability has been demonstrated in all series. For 51 eyes followed by Zaldivar et al., refraction was −0.90 D at 1 month, −0.91 D at 6 months, and −0.83 D at 12 months postoperatively. In all reported series, the refraction remained stable at each interval during the follow-up.


Quality of Vision


The level of patient satisfaction is very high. In the study by Arné and Lesueur, 55.7% of the patients were very satisfied, 36.2% were satisfied, and 6.9% moderately satisfied. No patient was dissatisfied.


Halos


The rate of subjective complaints, including glare and halos, varied from 2.4% for Zaldivar et al., 55% for Arné and Lesueur, and 25.8% for Hoyos. The rate of halos was higher when the size of the optical zone of the ICL was small.


Arné and Lesueur tested contrast sensitivity preoperatively with contact lenses and 6 months after surgery ( Fig. 31.3 ). The mean postoperative level without correction was higher than the mean preoperative level with correction; the difference was statistically significant for each level of luminance. Jiménez-Alfaro et al. evaluated contrast sensitivity in 20 eyes operated on for the correction of high myopia; they reported that contrast sensitivity increased after implantation of an ICL in all spatial frequencies when compared to preoperative contrast sensitivity with best spectacle correction.




Fig. 31.3


Contrast sensitivity before and after implantation.


Pallikaris et al. found no statistically significant difference in higher-order aberrations after PRL implantation.




Predictability


Predictability was good and results were relatively similar in all studies, as shown in the following publications.


Assetto et al. implanted 15 lenses in 14 patients. Average follow-up was 7 ± 1.95 months. Mean spherical equivalent was −15.3 D ± 3.1 D preoperatively, −2 D ± 1.5 D postoperatively. Only 31% of eyes had less than 1 D of residual myopia. However, an old model of lenses was used.


Rosen and Gore operated on 16 myopic eyes (−5.25 D to −14.50 D). At 3 months after surgery, refraction ranged from −1.25 D to +1 D; 56.2% of eyes were within 0.50 D from emmetropia.


Zaldivar et al. analyzed a cohort of 124 eyes; the mean follow-up period was 11 months (range, 1–36 months). The mean preoperative spherical equivalent was −13.38 ± 2.23 D (range, −8.50 D to −18.63 D). The target was emmetropia. The postoperative mean spherical equivalent was −0.78 D ± 0.87 D (range, +1.63 D to −3.50 D); 69% of the eyes were within 1 D and 44% within 0.50 D from emmetropia.


Arné and Lesueur implanted 58 eyes of 46 myopic patients. Follow-up ranged from 9 months to 2 years. Spherical equivalent was −13.85 D ± 4.61 D (range, −8 D to −19.21 D) preoperatively and −1.22 D ± 0.58 D postoperatively; 56.9 % of the eyes were within 1 D of emmetropia. Residual myopia was more than 2 D in 15.5% of the eyes.


Uusitalo et al. reported the results of ICL implantation in 38 eyes of 22 patients. The mean preoperative myopia was −15.10 D (range, −7.75 D to 29 D); the mean follow-up was 13.6 months (range, 6–24 months). Postoperatively, the mean spherical equivalent refraction was −2 D ± 2.48 D (range, +0.13 D to −13 D); 96.4% of the eyes were within 1 D and 85.7% within 0.5 D of emmetropia.


Pallikaris et al. evaluated the 1-year results of PRL implantation in 34 myopic eyes. They found a statistically significant reduction in the manifest refraction in spherical equivalent (preoperative: −14.70 D, range, −10.5 D to −20.75 D; postoperative: −0.61 D, range, −2.25 D to +1 D); 79% and 44% of the eyes were within 1 D and 0.5 D of target refraction, respectively.


Sanders et al. reported on 526 eyes with between 3.0 D and 20.0 D of myopia participating in the US Food and Drug Administration clinical trial of the ICL for myopia: 67.5% of patients were within 0.5 D and 88.2% were within 1.0 D of predicted refraction.


There were few studies on results of hyperopic ICL : Rosen and Gore operated on 9 hyperopic eyes (preoperative spherical equivalent [SE] range, +2.25 D to +5.62 D); 3 months postoperatively, refraction ranged from −0.12 D to +1 D.


Davidorf et al. implanted a collamer PIOL into 24 eyes with hyperopia greater than 3.50 D. The mean preoperative SE was +6.51 D ± 2.08 D (range, +3.75 D to +10.50 D). The mean postoperative SE was −0.39 D ± 1.29 D (range, +1.25 D to −3.88 D). Postoperatively, 79% of the eyes were within +1 D and 58% within +0.50 D from emmetropia. These results compare favorably with predicted results of the authors’ series of highly myopic eyes.


Gimbel and Ziémba reported one case of an astigmatic eye implanted with a posterior chamber PIOL. Manifest preoperative refraction was −9.25 (−2.25 × 98 degrees); 5 months after surgery, manifest refraction was +0.25 (−0.25 × 60 degrees).


Hoyos et al. presented the results of implantation of a PRL in 31 eyes (17 myopic, 14 hyperopic). The mean preoperative spherical equivalent was −18.46 D (range, −11.85 D to −26 D) for myopia, +7.77 D (range, +5.25 D to 11 D) for hyperopia. At 1 year, the mean postoperative spherical equivalent in the myopic group was −0.22 D (range, +1.50 to −2 D) and −0.38 (range +1.50 to −1.75 D).

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Oct 10, 2019 | Posted by in OPHTHALMOLOGY | Comments Off on Posterior Chamber Phakic Intraocular Lens
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