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Overcorrections with Radial Keratotomy
LEITERS
retractors upon completion of the capsulorhexis. I have yet to encounter an instance where the previously retracted iris, upon being freed, resulted in exposure difficulty. There are two reasons for this. Since sphincter damage associated with performing phacoemulsification over a retracted iris has been eliminated, the pupil can be safely stretched to a greater degree, allowing exposure adequate for a 5 to 6 mm capsulorhexis. The resultant intraoperative dilation thus effected is similar in mechanism to that achieved by the instrument stretching maneuvers advocated by some surgeons, although iris retractors generally accomplish this in a manner which is friendlier to the pupil. Second, as Dr. Masket has pointed out,2 it is the pupillary border opposite the incision site that provides the exposure needed for phacoemulsification. That objective is achieved since retractors remain in place at this site during this portion of the procedure. The sphincter of a pharmacologically well-dilated pupil is, to a degree, insulated from the phaco probe. It becomes vulnerable to damage, however, when the iris is put on stretch with retractors. Even without obvious anterior tenting of the iris, there can be sufficient phaco probe exposure to account for pupil-deforming sphincter damage. Mini-rents from retractor stretching alone, when they occur, are more like mini-sphincterotomies and generally have no pronounced effect on the postoperative pupillary dimension. Nevertheless, excessive retraction is to be avoided. Viscoelastics can be used to bow the iris posteriorly while other instrumentation is used, but, in this context, only routine removal of the subincisional iris retractors, after performing the capsulorhexis, will ensure that the sphincter is protected from phaco probe damage. Finally, I believe it is preferable to use a long-acting intraoperative miotic such as Miostat® (carbachol) in these cases. L. CORBIN, MD Los Angeles, California
WILLIAM
References 1. Masket S. Avoiding complications associated with iris retractor use in small pupil cataract extraction. J Cataract Refract Surg 1996; 22:168-171 2. Masket S. Preplaced inferior iris suture method for small pupil phacoemulsification. J Cataract Refract Surg 1992; 18:518-522
Overcorrections with Radial Keratotomy
E
I-Maghraby et al. 1 reported on a parallel study of radial keratotomy (RK) in one eye and photorefractive keratectomy (PRK) in the other to compare efficacy and safety of these two methods for reducing myopia (-1.00 to - 5.00 diopters [D)). The authors concluded that, while both methods were effective, PRK was more predictable and stable. What stood out for me in this study was that 6 of 33 RK eyes (18%) were overcorrected by more than 1.00 D after a single operation. This rate of overcorrection is high and had a direct bearing on the authors' conclusions. Why so many overcorrections with the RK eyes? One possibility is that a coin gauge was used to set the blades, and this maneuver can be done more accurately with a micron scope that may not have been available at the time of the study. Also, there were some perforations and optical zone incursions that may have affected results. Probably the most significant factor, however, was that the Thornton nomogram, which is designed for American-style incisions, was used with Russian-style incisions. This may account for the greater effect and overcorrections. After reading this paper, I retrieved from my own database 33 consecutive RK patients, preop -1.00 to -5.00 D with no T-cuts and at least 1 year postoperative, to match the study parameters. I found the largest overcorrection (SE) was +0.12 in unenhanced and enhanced eyes, with a range of +0.12 to -1.50 and 31 of 33 eyes between +0.12 and -0.50 D. These RKs were performed with centripetal incisions but with Casebeer nomograms, which are designed for Russian-style incisions. Verity et al. 2 reported on 395 patients in a prospective study of RK using bidirectional incisions and found 5 of 375 eyes or 1.3% overcorrected by greater than 1.00 D. The authors are to be commended for their fine study and honest reporting of results, but I do not think the RK results are optimal and therefore the conclusion of PRK over RK for this myopic range should not be extrapolated beyond the results of this study.
J CATARACT REFRACT SURG-VOL 22, JULY/AUGUST 1996
JAMES P. PULASKI,
MD
San Diego, California 653
LETTERS
References 1. El-Maghraby A, Salah T, Polit F, et al. Efficacy and safety of excimer laser photo refractive keratectomy and radial keratotomy for bilateral myopia.] Cataract Refract Surg 1996; 22:51-58 2. Verity SM, Talamo ]H, Arturo C, et al. The combined technique of radial keratotomy. Ophthalmology 1995; 102:1908-1915
This management is a further option to the possibilities outlined in the Consultation Section, but in the presence of a good refractive outcome from the original surgety and in the presence of reassurance from a vitreoretinal specialist, I believe it has advantages that deserve consideration.
Additional Consultation Responses
I
read with interest the Consultation Section that concerned a young patient with intermittent pupil capture of a posterior chamber three-piece intraocular lens (IOL) with polypropylene haptics. 1 Most of the discussants considered either medical therapy with miotics or exchange with an all poly(methyl methacrylate) (PMMA) lens. I believe there is a further option for this patient. Although we are not given any information about the refractive outcome of the original surgery, if the outcome were close to emmetropia with no significant astigmatism and a surgical option is to be considered, I believe the following may have some advantages. It would be technically possible following full mydriasis to fill the anterior chamber with a high viscosity viscoelastic material and through a small incision placed across the steepest meridian to make a 5 mm posterior capsulorhexis behind the existing IOL. To avoid vitreous prolapse, I would consider initially puncturing the capsule and then injecting viscoelastic material behind the posterior capsule to displace vitreous posteriorly. It should be possible to dislocate the optic through the posterior capsulorhexis while retaining the haptics in the ciliary sulcus. The advantage of this technique is that it could be done entirely through small incisions and would, I believe, be less traumatic than an IOL exchange with a large-optic PMMA lens that would require at least a 7 mm incision. The major disadvantage is that it breaches the posterior capsule in a highly myopic eye. Prior to considering this technique, I would ensure that the patient was examined by a vitreoretinal specialist with a view to confirming that a full posterior vitreous detachment had occurred and that there were no lesions predisposing to early retinal detachment. After such surgery the posterior capsulorhexis would be blocked by the IOL optic, which should prevent vitreous prolapse into the anterior segment and thereby reduce the chance of vitreous displacement and its potential problems. 654
CHARLES CLAOUE,
MA, MD, FRCS, FRCOPHTH
Romford, England
Reference 1. Masket S, ed. Consultation section.] Cataract Refract Surg 1996; 22:8-13
I
n a recent Consultation Sec"ion, the question of managing episodic pupillary capture in a patient with a poly(methyl methacrylate) intraocular lens (IOL) with polypropylene (Prolene®) haptics was posed. I am distressed that the majority of the consultants suggested a lens exchange with no examination of the position, type, or character of the haptics. In 1990, Pavlin and coauthors described subsurface ultrasound microscopic imaging of the intact eye. The technique describes the now clinically available ultrasound biomicroscopic examination of the anterior segment, which has been well documented to visualize the position and type of haptics that are located in the ciliary sulcus,z-4 These papers clearly demonstrate the value of determining whether the haptic is located in the ciliary sulcus or whether it is incarcerated in the ciliary body. Such determination is necessary to avoid traumatic removal of the haptic with possible massive bleeding. Since this ultrasonic biomicroscope is now clinically available, I feel it is inappropriate to suggest IOL exchange without examination and knowledge of the haptics of the existing IOL. S. DIXON, MD Toronto, Ontario, Canada
WILLIAM
References 1. Pavlin C], Sherar MD, Foster FS. Subsurface ultrasound microscopic imaging of the intact eye. Ophthalmology 1990; 97 :244250 2. Pavlin C], Sherar MD, Harasiewicz K, Foster FS. Clinical use of ultrasound biomicroscopy. Ophthalmology 1991; 98:287-295 3. Pavlin C], Rootman D, ArshinoffS, et al. Determination of haptic position of transsclerally fixated posterior chamber intraocular lenses by ultrasound biomicroscopy. ] Cataract Refract Surg 1993; 19:573-577
J CATARACT REFRACT SURG-VOL 22, JULY/AUGUST 1996
retractors upon completion of the capsulorhexis. I have yet to encounter an instance where the previously retracted iris, upon being freed, resulted in exposure difficulty. There are two reasons for this. Since sphincter damage associated with performing phacoemulsification over a retracted iris has been eliminated, the pupil can be safely stretched to a greater degree, allowing exposure adequate for a 5 to 6 mm capsulorhexis. The resultant intraoperative dilation thus effected is similar in mechanism to that achieved by the instrument stretching maneuvers advocated by some surgeons, although iris retractors generally accomplish this in a manner which is friendlier to the pupil. Second, as Dr. Masket has pointed out,2 it is the pupillary border opposite the incision site that provides the exposure needed for phacoemulsification. That objective is achieved since retractors remain in place at this site during this portion of the procedure. The sphincter of a pharmacologically well-dilated pupil is, to a degree, insulated from the phaco probe. It becomes vulnerable to damage, however, when the iris is put on stretch with retractors. Even without obvious anterior tenting of the iris, there can be sufficient phaco probe exposure to account for pupil-deforming sphincter damage. Mini-rents from retractor stretching alone, when they occur, are more like mini-sphincterotomies and generally have no pronounced effect on the postoperative pupillary dimension. Nevertheless, excessive retraction is to be avoided. Viscoelastics can be used to bow the iris posteriorly while other instrumentation is used, but, in this context, only routine removal of the subincisional iris retractors, after performing the capsulorhexis, will ensure that the sphincter is protected from phaco probe damage. Finally, I believe it is preferable to use a long-acting intraoperative miotic such as Miostat® (carbachol) in these cases. L. CORBIN, MD Los Angeles, California
WILLIAM
References 1. Masket S. Avoiding complications associated with iris retractor use in small pupil cataract extraction. J Cataract Refract Surg 1996; 22:168-171 2. Masket S. Preplaced inferior iris suture method for small pupil phacoemulsification. J Cataract Refract Surg 1992; 18:518-522
Overcorrections with Radial Keratotomy
E
I-Maghraby et al. 1 reported on a parallel study of radial keratotomy (RK) in one eye and photorefractive keratectomy (PRK) in the other to compare efficacy and safety of these two methods for reducing myopia (-1.00 to - 5.00 diopters [D)). The authors concluded that, while both methods were effective, PRK was more predictable and stable. What stood out for me in this study was that 6 of 33 RK eyes (18%) were overcorrected by more than 1.00 D after a single operation. This rate of overcorrection is high and had a direct bearing on the authors' conclusions. Why so many overcorrections with the RK eyes? One possibility is that a coin gauge was used to set the blades, and this maneuver can be done more accurately with a micron scope that may not have been available at the time of the study. Also, there were some perforations and optical zone incursions that may have affected results. Probably the most significant factor, however, was that the Thornton nomogram, which is designed for American-style incisions, was used with Russian-style incisions. This may account for the greater effect and overcorrections. After reading this paper, I retrieved from my own database 33 consecutive RK patients, preop -1.00 to -5.00 D with no T-cuts and at least 1 year postoperative, to match the study parameters. I found the largest overcorrection (SE) was +0.12 in unenhanced and enhanced eyes, with a range of +0.12 to -1.50 and 31 of 33 eyes between +0.12 and -0.50 D. These RKs were performed with centripetal incisions but with Casebeer nomograms, which are designed for Russian-style incisions. Verity et al. 2 reported on 395 patients in a prospective study of RK using bidirectional incisions and found 5 of 375 eyes or 1.3% overcorrected by greater than 1.00 D. The authors are to be commended for their fine study and honest reporting of results, but I do not think the RK results are optimal and therefore the conclusion of PRK over RK for this myopic range should not be extrapolated beyond the results of this study.
J CATARACT REFRACT SURG-VOL 22, JULY/AUGUST 1996
JAMES P. PULASKI,
MD
San Diego, California 653
LETTERS
References 1. El-Maghraby A, Salah T, Polit F, et al. Efficacy and safety of excimer laser photo refractive keratectomy and radial keratotomy for bilateral myopia.] Cataract Refract Surg 1996; 22:51-58 2. Verity SM, Talamo ]H, Arturo C, et al. The combined technique of radial keratotomy. Ophthalmology 1995; 102:1908-1915
This management is a further option to the possibilities outlined in the Consultation Section, but in the presence of a good refractive outcome from the original surgety and in the presence of reassurance from a vitreoretinal specialist, I believe it has advantages that deserve consideration.
Additional Consultation Responses
I
read with interest the Consultation Section that concerned a young patient with intermittent pupil capture of a posterior chamber three-piece intraocular lens (IOL) with polypropylene haptics. 1 Most of the discussants considered either medical therapy with miotics or exchange with an all poly(methyl methacrylate) (PMMA) lens. I believe there is a further option for this patient. Although we are not given any information about the refractive outcome of the original surgery, if the outcome were close to emmetropia with no significant astigmatism and a surgical option is to be considered, I believe the following may have some advantages. It would be technically possible following full mydriasis to fill the anterior chamber with a high viscosity viscoelastic material and through a small incision placed across the steepest meridian to make a 5 mm posterior capsulorhexis behind the existing IOL. To avoid vitreous prolapse, I would consider initially puncturing the capsule and then injecting viscoelastic material behind the posterior capsule to displace vitreous posteriorly. It should be possible to dislocate the optic through the posterior capsulorhexis while retaining the haptics in the ciliary sulcus. The advantage of this technique is that it could be done entirely through small incisions and would, I believe, be less traumatic than an IOL exchange with a large-optic PMMA lens that would require at least a 7 mm incision. The major disadvantage is that it breaches the posterior capsule in a highly myopic eye. Prior to considering this technique, I would ensure that the patient was examined by a vitreoretinal specialist with a view to confirming that a full posterior vitreous detachment had occurred and that there were no lesions predisposing to early retinal detachment. After such surgery the posterior capsulorhexis would be blocked by the IOL optic, which should prevent vitreous prolapse into the anterior segment and thereby reduce the chance of vitreous displacement and its potential problems. 654
CHARLES CLAOUE,
MA, MD, FRCS, FRCOPHTH
Romford, England
Reference 1. Masket S, ed. Consultation section.] Cataract Refract Surg 1996; 22:8-13
I
n a recent Consultation Sec"ion, the question of managing episodic pupillary capture in a patient with a poly(methyl methacrylate) intraocular lens (IOL) with polypropylene (Prolene®) haptics was posed. I am distressed that the majority of the consultants suggested a lens exchange with no examination of the position, type, or character of the haptics. In 1990, Pavlin and coauthors described subsurface ultrasound microscopic imaging of the intact eye. The technique describes the now clinically available ultrasound biomicroscopic examination of the anterior segment, which has been well documented to visualize the position and type of haptics that are located in the ciliary sulcus,z-4 These papers clearly demonstrate the value of determining whether the haptic is located in the ciliary sulcus or whether it is incarcerated in the ciliary body. Such determination is necessary to avoid traumatic removal of the haptic with possible massive bleeding. Since this ultrasonic biomicroscope is now clinically available, I feel it is inappropriate to suggest IOL exchange without examination and knowledge of the haptics of the existing IOL. S. DIXON, MD Toronto, Ontario, Canada
WILLIAM
References 1. Pavlin C], Sherar MD, Foster FS. Subsurface ultrasound microscopic imaging of the intact eye. Ophthalmology 1990; 97 :244250 2. Pavlin C], Sherar MD, Harasiewicz K, Foster FS. Clinical use of ultrasound biomicroscopy. Ophthalmology 1991; 98:287-295 3. Pavlin C], Rootman D, ArshinoffS, et al. Determination of haptic position of transsclerally fixated posterior chamber intraocular lenses by ultrasound biomicroscopy. ] Cataract Refract Surg 1993; 19:573-577
J CATARACT REFRACT SURG-VOL 22, JULY/AUGUST 1996