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Effect of blue staining of expandable hydrophilic intraocular lenses on contrast sensitivity and glare vision
Effect of blue staining of expandable hydrophilic intraocular lenses on contrast sensitivity and glare vision Tiago Bisol, MD, Renata A. Rezende, MD, Jaime Guedes, MD, Adalmir M. Dantas, MD, PhD Purpose: To evaluate the effect of trypan blue staining of expandable hydrophilic acrylic intraocular lenses (IOLs) on contrast sensitivity and glare. Setting: Department of Ophthalmology, Federal University, and Oculistas Associados, Rio de Janeiro, Brazil. Methods: Phacoemulsification with expandable hydrophilic IOL implantation was performed in 19 eyes. Group 1 (stained group) consisted of 12 eyes with the IOL unintentionally stained by trypan blue 0.1% solution during surgery; Group 2 (unstained group) consisted of 7 eyes with IOLs that were not stained because trypan blue was not used during surgery. The eyes were examined postoperatively for Snellen best corrected visual acuity (BCVA), contrast sensitivity BCVA, and glare vision. The examiners were masked to whether the IOL was stained by trypan blue. Inclusion criteria included a BCVA of 20/30 or better 1 month postoperatively. Patients who had other ocular pathology or previous ocular surgery were excluded from the study. Results: The mean postoperative BCVA was 20/24 in the stained group and 20/23 in the unstained group (P ⫽ .73). The mean contrast sensitivity visual acuity was 20/31 in the stained group and 20/26 in unstained group (P ⫽ .10). The mean glare visual acuity was 20/75 and 20/33, respectively (P ⫽ .03). Conclusions: Patients with expandable hydrophilic acrylic IOLs stained with trypan blue performed significantly worse on a glare vision test than patients whose IOLs were not stained. Cataract surgeons should avoid using trypan blue with this IOL type. J Cataract Refract Surg 2004; 30:1732–1735 2004 ASCRS and ESCRS
I
n the past 3 decades, phacoemulsification has undergone modifications that have increased its safety and efficacy. It is considered the best technique for the Accepted for publication December 17, 2003. From Rio de Janeiro, Brazil. Presented in part at the Symposium on Cataract, IOL and Refractive Surgery, Philadelphia, Pennsylvania, USA, June 2002. None of the authors has a financial or proprietary interest in any material or method mentioned. Flavio Rezende, MD, was a participating investigator. Reprint requests to Tiago Bisol, MD, Rua Visconde de Silva, 321 apt 201, CEP 22271-090, Rio de Janeiro, RJ, Brazil. E-mail: tbisol@ hotmail.com. 2004 ASCRS and ESCRS Published by Elsevier Inc.
management of visually significant cataract.1,2 Continuous curvilinear capsulorhexis (CCC) is a critical step in phacoemulsification cataract extraction.3 Inadequate visualization of the capsule while performing CCC can result in incomplete capsulorhexis, which has a high risk for radial capsule tears toward or beyond the lens equator and associated complications.4 Many techniques have been used to enhance visualization of the capsulorhexis. The use of anterior capsule staining agents such as fluorescein sodium 2%,5,6 indocyanine green (ICG) 0.5%,7 and trypan blue 0.1%8 during phacoemulsification increases the safety margin, assists cataract surgeons in cataractous eyes with poor red fundus reflex,9 and helps trainee surgeons.10 The 0886-3350/04/$–see front matter doi:10.1016/j.jcrs.2003.12.036
BLUE STAINING, CONTRAST SENSITIVITY, AND GLARE VISION
use of trypan blue 0.1% as a capsule dye is not approved by the U.S. Food and Drug Administration (FDA) but it can be used in Brazil. Trypan blue provides better visualization of the capsulorhexis than fluorescein and is less expensive than ICG. No significant toxicity to the corneal endothelium or other adverse effects have been reported.11,12 Many surgeons have adopted the use of hydrophilic acrylic intraocular lenses (IOLs) because they are easy to handle, have excellent biocompatibility (M. Blumenthal, MD, “Expandable Acrylic Acqua IOL Facilitates Implant Procedure,” Ocular Surgery News Europe/Asia-Pacific Edition, July 2001),13 and are not costly. The Acqua威 IOL (Mediphacos) is a plate-designed expandable hydrophilic acrylic IOL manufactured from copolymer hydrophilic acrylic (Acryfil CQ) with a high water content (73.5%). It is approved by the European Community but not by the U.S. FDA. Its dimensions in a dehydrated state are 3.2 mm ⫻ 7.1 mm. Once the IOL is implanted, it reacts with balanced saline solution and aqueous, leading to hydration until it reaches final hydrated state dimensions of 5.1 mm ⫻ 10.8 mm after 20 minutes. However, complete hydration of the optic occurs 8 to 24 hours after implantation.14 The use of an expandable IOL after a capsule staining procedure raises the question of whether IOL material absorbs the dye.6 The impregnation of expandable hydrophilic IOLs with trypan blue during its expansion (hydration) has been reported by Werner et al.14 This study evaluated the effect of trypan-bluestained expandable hydrophilic acrylic IOLs on contrast sensitivity and glare vision. To our knowledge, this is the first study of this effect.
to the stained group. Eyes in which trypan blue was used during surgery but did not have the IOLs stained were not included in the study. In the control group (unstained group), phacoemulsification was performed without using trypan blue and the IOLs were not stained. Inclusion criteria were uneventful phacoemulsification with implantation of hydrogel expandable IOLs and a Snellen best corrected visual acuity (BCVA) of 20/30 or better 1 month postoperatively. Exclusion criteria were a history of glaucoma, age-related macular degeneration, a diagnosis of diabetic or hypertensive retinopathy, and other previous ocular surgery. All patients had phacoemulsification performed by a single surgeon (J.G.) through a 12 o’clock corneal tunnel incision using peribulbar anesthesia. The ophthalmic viscosurgical device used in all cases was hydroxypropyl methylcellulose 2%. The postoperative examination was performed by an ophthalmologist (T.B. or R.A.R.) who was masked to whether the IOL was stained by trypan blue. The time between surgery and examination ranged from 1 to 7 months in both groups, with a mean of 2.6 months in the stained group and 3.1 months in the unstained group (not a statistically significant difference). Examination consisted of Snellen BCVA, contrast sensitivity, and a glare vision test. Contrast sensitivity and glare vision were tested using Vector Vision CSV-1000 equipment15 performed from an 8-foot distance, with charts consisting of vertical bars distributed in 4 patterns of frequency with gradual contrast reduction. The lowest contrast identified by the patient on the 6 cycles per degree frequency was noted. The glare test was done with the same contrast charts at the same distance but with light shined from the chart’s sides directed to the patient, creating a glare effect. Statistical analysis was done with the EPI-INFO program, version 6.04d, using analysis of variance, chi-square, and Kruskal-Wallis tests, with a 95% statistical significance. For comparisons of visual acuity results, data were converted from feet notation to logarithm of the minimal angle of resolution (logMAR).
Patients and Methods Nineteen eyes (15 patients) with phacoemulsification performed between July 27, 2001, and June 15, 2002, were examined. Group 1 (stained group) consisted of 12 eyes with the IOL unintentionally stained with trypan blue 0.1% solution (Ophthalmos) during surgery; Group 2 (unstained group) consisted of 7 eyes that did not have a stain on the IOL because trypan blue was not used during surgery. In Group 1, staining of the IOL occurred unintentionally during surgery because trypan blue remained in the anterior chamber during implantation and hydration of the hydrophilic IOL, which is a complication reported by Werner et al.14 Staining of the IOLs was noted during the postoperative follow-up, and these patients were subsequently assigned
Results The mean patient age in the stained group was 64.9 years ⫾ 6.9 (SD), and the mean age in the unstained group was 71.3 ⫾ 7.1 years. There were 9 men and 3 women in the stained group and 4 men and 3 women in the unstained group (Table 1). The mean Snellen BCVA was 20/24 in the stained group and 20/23 in the unstained group (P ⫽ 0.73). The mean contrast sensitivity visual acuity (CSVA) was 20/31 in the stained group and 20/26 in the unstained group (P ⫽ 0.10). The mean glare visual acuity (GVA)
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Table 1. Demographic data. Demographic Mean age (years) ⫾ SD Sex (M/F)
Stained (n ⫽ 12)
Unstained (n ⫽ 7)
P Value
64.9 ⫾ 6.9
71.3 ⫾ 7.1
.07
9/3
4/3
.61
was 20/75 in the stained group and 20/33 in the unstained group (P ⫽ 0.03) (Table 2).
Discussion Trypan blue staining of expandable hydrophilic acrylic IOLs occurs during contact of the expandable hydrophilic material with the dye remaining in the anterior chamber. Washing the anterior chamber with saline solution did not prevent staining. Although some patients complained of bluish vision and the IOL appeared blue on biomicroscopy, good Snellen visual acuity was usually achieved. Although the patients in both groups had comparable Snellen BCVA results in our study, the stained IOL group had worse CSVA results (20/31) than the unstained group (20/26) (P ⫽ .10). This trend toward significance was observed even though the sample was small. Glare vision testing, however, showed a statistically and clinically significant difference between the 2 groups: The stained group had a GVA of 20/75, and the unstained group had a GVA of 20/33 (P ⫽ .03). This significance in such a small number of patients indicates a great impairment of glare vision in the stained IOL group. The staining of expandable hydrophilic acrylic IOLs with trypan blue is not frequently reported. Werner et al.14 describe explantation of an Acqua IOL because of reduced visual acuity from trypan blue staining. In vitro 24-hour balanced saline solution immersion could not remove IOL discoloration.14 Fritz6,16 showed experimentally that acrylic IOLs are also susceptible to trypan blue staining that leads to great reduction on red and
green light transmission. He suggests these IOLs be avoided when the dye is used. Intensity of IOL discoloring was not graded in this study, but all patients had good Snellen visual acuity (a BCVA of 20/30 or better was part of the inclusion criteria), which does not necessarily mean good visual performance. The latter is better evaluated by a contrast sensitivity and glare test, the results of which were worse in the stained IOL group. We are not aware of another study in the literature regarding visual acuity, contrast sensitivity or glare testing, and stained IOLs. Although our sample size was small, these findings should be considered when trypan blue may be used in combination with expandable hydrophilic acrylic IOL implantation. In summary, patients who had phacoemulsification performed with the implantation of Acqua hydrophilic expandable acrylic IOLs stained with trypan blue performed significantly worse in a glare vision test than patients whose IOLs were not stained, without significant difference in the contrast sensitivity test. These results suggest that the implantation of expandable hydrophilic acrylic IOLs should be avoided when trypan blue is used as a staining agent until further studies confirm or contradict this finding.
References 1. Jacob S, Agarwal A, Agarwal A, et al. Trypan blue as adjunct for safe phacoemulsification in eyes with white cataract. J Cataract Refract Surg 2002; 28:1819–1825 2. Werner L, Pandey SK, Escobar-Gomez M, et al. Dyeenhanced cataract surgery. Part 2: learning critical steps of phacoemulsification. J Cataract Refract Surg 2000; 26:1060–1065
Table 2. Results of mean visual acuity, CSVA, and GVA in stained and unstained IOLs. Stained (n ⫽ 12)
Nonstained (n ⫽ 7)
P value
Snellen BCVA
20/24
20/23
.73
Contrast sensitivity BCVA
20/31
20/26
.10
Glare BCVA
20/75
20/33
.03
Acuity
BCVA ⫽ best corrected visual acuity
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3. Gimbel HV, Neuhann T. Development, advantages, and methods of the continuous circular capsulorhexis technique. J Cataract Refract Surg 1990; 16:31–37 4. Rao SK, Padmanabhan P. Capsulorhexis in eyes with phacomorphic glaucoma. J Cataract Refract Surg 1998; 24:882–884 5. Hoffer KJ, McFarland JE. Intracameral subcapsular fluorescein staining for improved visualization during capsulorhexis in mature cataracts [letter]. J Cataract Refract Surg 1993; 19:566 6. Fritz WL. Fluorescein blue, light-assisted capsulorhexis for mature or hypermature cataract. J Cataract Refract Surg 1998; 24:19–20 7. Horiguchi M, Miyake K, Ohta I, Ito Y. Staining of the lens capsule for circular continuous capsulorhexis in eyes with white cataract. Arch Ophthalmol 1998; 116:535– 537 8. Melles GRJ, de Waard PWT, Pameyer JH, Beekhuis WH. Trypan blue capsule staining to visualize the capsulohrexis in cataract surgery. J Cataract Refract Surg 1999; 25:7–9 9. Pandey SK, Werner L, Escobar-Gomez M, et al. Dyeenhanced cataract surgery. Part 1: anterior capsule staining for capsulorhexis in advanced/white cataract. J Cataract Refract Surg 2000; 26:1052–1059
10. Dada T, Ray M, Bhartiya P, Vajpayee RB. Trypan-blueassisted capsulorhexis for trainee phacoemulsification surgeons [letter]. J Cataract Refract Surg 2002; 28:575– 576 11. Norn MS. Peroperative trypan blue vital staining of corneal endothelium; eight years’ follow-up. Acta Ophthalmol 1980; 58:550–555 12. Van Dooren BTH, de Waard PWT, Poort-van Nouhuys H, et al. Corneal endothelial cell density after trypan blue capsule staining in cataract surgery [letter]. J Cataract Refract Surg 2002; 28:574–575 13. Assia EI, Blumenthal M, Apple DJ. Effect of expandable full-size intraocular lenses on lens centration and capsule opacification in rabbits. J Cataract Refract Surg 1999; 25:347–356 14. Werner L, Apple DJ, Crema AS, et al. Permanent blue discoloration of a hydrogel intraocular lens by intraoperative trypan blue. J Cataract Refract Surg 2002; 28:1279– 1286 15. Pomerance GN, Evans DW. Test-retest reliability of the CSV-1000 contrast test and its relationship to glaucoma therapy. Invest Ophthalmol Vis Sci 1994; 35:3357– 3361 16. Fritz WL. Digital image analysis of trypan blue and fluorescein staining of anterior lens capsules and intraocular lenses. J Cataract Refract Surg 2002; 28:1034–1038
J CATARACT REFRACT SURG—VOL 30, AUGUST 2004
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I
n the past 3 decades, phacoemulsification has undergone modifications that have increased its safety and efficacy. It is considered the best technique for the Accepted for publication December 17, 2003. From Rio de Janeiro, Brazil. Presented in part at the Symposium on Cataract, IOL and Refractive Surgery, Philadelphia, Pennsylvania, USA, June 2002. None of the authors has a financial or proprietary interest in any material or method mentioned. Flavio Rezende, MD, was a participating investigator. Reprint requests to Tiago Bisol, MD, Rua Visconde de Silva, 321 apt 201, CEP 22271-090, Rio de Janeiro, RJ, Brazil. E-mail: tbisol@ hotmail.com. 2004 ASCRS and ESCRS Published by Elsevier Inc.
management of visually significant cataract.1,2 Continuous curvilinear capsulorhexis (CCC) is a critical step in phacoemulsification cataract extraction.3 Inadequate visualization of the capsule while performing CCC can result in incomplete capsulorhexis, which has a high risk for radial capsule tears toward or beyond the lens equator and associated complications.4 Many techniques have been used to enhance visualization of the capsulorhexis. The use of anterior capsule staining agents such as fluorescein sodium 2%,5,6 indocyanine green (ICG) 0.5%,7 and trypan blue 0.1%8 during phacoemulsification increases the safety margin, assists cataract surgeons in cataractous eyes with poor red fundus reflex,9 and helps trainee surgeons.10 The 0886-3350/04/$–see front matter doi:10.1016/j.jcrs.2003.12.036
BLUE STAINING, CONTRAST SENSITIVITY, AND GLARE VISION
use of trypan blue 0.1% as a capsule dye is not approved by the U.S. Food and Drug Administration (FDA) but it can be used in Brazil. Trypan blue provides better visualization of the capsulorhexis than fluorescein and is less expensive than ICG. No significant toxicity to the corneal endothelium or other adverse effects have been reported.11,12 Many surgeons have adopted the use of hydrophilic acrylic intraocular lenses (IOLs) because they are easy to handle, have excellent biocompatibility (M. Blumenthal, MD, “Expandable Acrylic Acqua IOL Facilitates Implant Procedure,” Ocular Surgery News Europe/Asia-Pacific Edition, July 2001),13 and are not costly. The Acqua威 IOL (Mediphacos) is a plate-designed expandable hydrophilic acrylic IOL manufactured from copolymer hydrophilic acrylic (Acryfil CQ) with a high water content (73.5%). It is approved by the European Community but not by the U.S. FDA. Its dimensions in a dehydrated state are 3.2 mm ⫻ 7.1 mm. Once the IOL is implanted, it reacts with balanced saline solution and aqueous, leading to hydration until it reaches final hydrated state dimensions of 5.1 mm ⫻ 10.8 mm after 20 minutes. However, complete hydration of the optic occurs 8 to 24 hours after implantation.14 The use of an expandable IOL after a capsule staining procedure raises the question of whether IOL material absorbs the dye.6 The impregnation of expandable hydrophilic IOLs with trypan blue during its expansion (hydration) has been reported by Werner et al.14 This study evaluated the effect of trypan-bluestained expandable hydrophilic acrylic IOLs on contrast sensitivity and glare vision. To our knowledge, this is the first study of this effect.
to the stained group. Eyes in which trypan blue was used during surgery but did not have the IOLs stained were not included in the study. In the control group (unstained group), phacoemulsification was performed without using trypan blue and the IOLs were not stained. Inclusion criteria were uneventful phacoemulsification with implantation of hydrogel expandable IOLs and a Snellen best corrected visual acuity (BCVA) of 20/30 or better 1 month postoperatively. Exclusion criteria were a history of glaucoma, age-related macular degeneration, a diagnosis of diabetic or hypertensive retinopathy, and other previous ocular surgery. All patients had phacoemulsification performed by a single surgeon (J.G.) through a 12 o’clock corneal tunnel incision using peribulbar anesthesia. The ophthalmic viscosurgical device used in all cases was hydroxypropyl methylcellulose 2%. The postoperative examination was performed by an ophthalmologist (T.B. or R.A.R.) who was masked to whether the IOL was stained by trypan blue. The time between surgery and examination ranged from 1 to 7 months in both groups, with a mean of 2.6 months in the stained group and 3.1 months in the unstained group (not a statistically significant difference). Examination consisted of Snellen BCVA, contrast sensitivity, and a glare vision test. Contrast sensitivity and glare vision were tested using Vector Vision CSV-1000 equipment15 performed from an 8-foot distance, with charts consisting of vertical bars distributed in 4 patterns of frequency with gradual contrast reduction. The lowest contrast identified by the patient on the 6 cycles per degree frequency was noted. The glare test was done with the same contrast charts at the same distance but with light shined from the chart’s sides directed to the patient, creating a glare effect. Statistical analysis was done with the EPI-INFO program, version 6.04d, using analysis of variance, chi-square, and Kruskal-Wallis tests, with a 95% statistical significance. For comparisons of visual acuity results, data were converted from feet notation to logarithm of the minimal angle of resolution (logMAR).
Patients and Methods Nineteen eyes (15 patients) with phacoemulsification performed between July 27, 2001, and June 15, 2002, were examined. Group 1 (stained group) consisted of 12 eyes with the IOL unintentionally stained with trypan blue 0.1% solution (Ophthalmos) during surgery; Group 2 (unstained group) consisted of 7 eyes that did not have a stain on the IOL because trypan blue was not used during surgery. In Group 1, staining of the IOL occurred unintentionally during surgery because trypan blue remained in the anterior chamber during implantation and hydration of the hydrophilic IOL, which is a complication reported by Werner et al.14 Staining of the IOLs was noted during the postoperative follow-up, and these patients were subsequently assigned
Results The mean patient age in the stained group was 64.9 years ⫾ 6.9 (SD), and the mean age in the unstained group was 71.3 ⫾ 7.1 years. There were 9 men and 3 women in the stained group and 4 men and 3 women in the unstained group (Table 1). The mean Snellen BCVA was 20/24 in the stained group and 20/23 in the unstained group (P ⫽ 0.73). The mean contrast sensitivity visual acuity (CSVA) was 20/31 in the stained group and 20/26 in the unstained group (P ⫽ 0.10). The mean glare visual acuity (GVA)
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Table 1. Demographic data. Demographic Mean age (years) ⫾ SD Sex (M/F)
Stained (n ⫽ 12)
Unstained (n ⫽ 7)
P Value
64.9 ⫾ 6.9
71.3 ⫾ 7.1
.07
9/3
4/3
.61
was 20/75 in the stained group and 20/33 in the unstained group (P ⫽ 0.03) (Table 2).
Discussion Trypan blue staining of expandable hydrophilic acrylic IOLs occurs during contact of the expandable hydrophilic material with the dye remaining in the anterior chamber. Washing the anterior chamber with saline solution did not prevent staining. Although some patients complained of bluish vision and the IOL appeared blue on biomicroscopy, good Snellen visual acuity was usually achieved. Although the patients in both groups had comparable Snellen BCVA results in our study, the stained IOL group had worse CSVA results (20/31) than the unstained group (20/26) (P ⫽ .10). This trend toward significance was observed even though the sample was small. Glare vision testing, however, showed a statistically and clinically significant difference between the 2 groups: The stained group had a GVA of 20/75, and the unstained group had a GVA of 20/33 (P ⫽ .03). This significance in such a small number of patients indicates a great impairment of glare vision in the stained IOL group. The staining of expandable hydrophilic acrylic IOLs with trypan blue is not frequently reported. Werner et al.14 describe explantation of an Acqua IOL because of reduced visual acuity from trypan blue staining. In vitro 24-hour balanced saline solution immersion could not remove IOL discoloration.14 Fritz6,16 showed experimentally that acrylic IOLs are also susceptible to trypan blue staining that leads to great reduction on red and
green light transmission. He suggests these IOLs be avoided when the dye is used. Intensity of IOL discoloring was not graded in this study, but all patients had good Snellen visual acuity (a BCVA of 20/30 or better was part of the inclusion criteria), which does not necessarily mean good visual performance. The latter is better evaluated by a contrast sensitivity and glare test, the results of which were worse in the stained IOL group. We are not aware of another study in the literature regarding visual acuity, contrast sensitivity or glare testing, and stained IOLs. Although our sample size was small, these findings should be considered when trypan blue may be used in combination with expandable hydrophilic acrylic IOL implantation. In summary, patients who had phacoemulsification performed with the implantation of Acqua hydrophilic expandable acrylic IOLs stained with trypan blue performed significantly worse in a glare vision test than patients whose IOLs were not stained, without significant difference in the contrast sensitivity test. These results suggest that the implantation of expandable hydrophilic acrylic IOLs should be avoided when trypan blue is used as a staining agent until further studies confirm or contradict this finding.
References 1. Jacob S, Agarwal A, Agarwal A, et al. Trypan blue as adjunct for safe phacoemulsification in eyes with white cataract. J Cataract Refract Surg 2002; 28:1819–1825 2. Werner L, Pandey SK, Escobar-Gomez M, et al. Dyeenhanced cataract surgery. Part 2: learning critical steps of phacoemulsification. J Cataract Refract Surg 2000; 26:1060–1065
Table 2. Results of mean visual acuity, CSVA, and GVA in stained and unstained IOLs. Stained (n ⫽ 12)
Nonstained (n ⫽ 7)
P value
Snellen BCVA
20/24
20/23
.73
Contrast sensitivity BCVA
20/31
20/26
.10
Glare BCVA
20/75
20/33
.03
Acuity
BCVA ⫽ best corrected visual acuity
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3. Gimbel HV, Neuhann T. Development, advantages, and methods of the continuous circular capsulorhexis technique. J Cataract Refract Surg 1990; 16:31–37 4. Rao SK, Padmanabhan P. Capsulorhexis in eyes with phacomorphic glaucoma. J Cataract Refract Surg 1998; 24:882–884 5. Hoffer KJ, McFarland JE. Intracameral subcapsular fluorescein staining for improved visualization during capsulorhexis in mature cataracts [letter]. J Cataract Refract Surg 1993; 19:566 6. Fritz WL. Fluorescein blue, light-assisted capsulorhexis for mature or hypermature cataract. J Cataract Refract Surg 1998; 24:19–20 7. Horiguchi M, Miyake K, Ohta I, Ito Y. Staining of the lens capsule for circular continuous capsulorhexis in eyes with white cataract. Arch Ophthalmol 1998; 116:535– 537 8. Melles GRJ, de Waard PWT, Pameyer JH, Beekhuis WH. Trypan blue capsule staining to visualize the capsulohrexis in cataract surgery. J Cataract Refract Surg 1999; 25:7–9 9. Pandey SK, Werner L, Escobar-Gomez M, et al. Dyeenhanced cataract surgery. Part 1: anterior capsule staining for capsulorhexis in advanced/white cataract. J Cataract Refract Surg 2000; 26:1052–1059
10. Dada T, Ray M, Bhartiya P, Vajpayee RB. Trypan-blueassisted capsulorhexis for trainee phacoemulsification surgeons [letter]. J Cataract Refract Surg 2002; 28:575– 576 11. Norn MS. Peroperative trypan blue vital staining of corneal endothelium; eight years’ follow-up. Acta Ophthalmol 1980; 58:550–555 12. Van Dooren BTH, de Waard PWT, Poort-van Nouhuys H, et al. Corneal endothelial cell density after trypan blue capsule staining in cataract surgery [letter]. J Cataract Refract Surg 2002; 28:574–575 13. Assia EI, Blumenthal M, Apple DJ. Effect of expandable full-size intraocular lenses on lens centration and capsule opacification in rabbits. J Cataract Refract Surg 1999; 25:347–356 14. Werner L, Apple DJ, Crema AS, et al. Permanent blue discoloration of a hydrogel intraocular lens by intraoperative trypan blue. J Cataract Refract Surg 2002; 28:1279– 1286 15. Pomerance GN, Evans DW. Test-retest reliability of the CSV-1000 contrast test and its relationship to glaucoma therapy. Invest Ophthalmol Vis Sci 1994; 35:3357– 3361 16. Fritz WL. Digital image analysis of trypan blue and fluorescein staining of anterior lens capsules and intraocular lenses. J Cataract Refract Surg 2002; 28:1034–1038
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