Laser Cataract Surgery: Curse of the Small Pupil

Abstract

Letters to the Editor Free H. Burkhard Dick, MD, PhD; Ronald D. Gerste, MD; Tim Schultz, MD Dr. Dick is a member of the medical advisory board of OptiMedica, Sunnyvale, California. The remaining authors have no financial or proprietary interest in the materials presented herein. The introduction of the femtosecond laser is the latest step on the journey to refinement in cataract surgery, to ever more predictable refractive results, to a higher precision in the two crucial steps of the procedure (capsulotomy and lens fragmentation), and to higher patient satisfaction in a clientele that comes to us with the highest expectations in postoperative visual acuity. Most of us who are operating with a femtosecond laser, irrespective of which system, cannot help being astounded by the ease of the procedure and the increased safety for the patient, who is exposed to just a fraction of the ultrasound energy applied in conventional cataract surgery—and in many cases (91% of operations in one of our series)¹ to no ultrasound at all. However, there is one drop of bitterness in the chalice of femtosecond laser-assisted cataract surgery: the small pupil. If the pupil is smaller than the intended diameter of the laser-guided capsulotomy, the surgeon is in trouble. But from where do the causes of this problem arise—is it the patient or the laser? We consider it important for all cataract surgeons to use well-defined terminology to be able to discuss potential intraoperative or postoperative complications, their prevention, and their therapy—and refer to the same situation, the same challenges. First, it is obvious that we should distinguish between a small pupil as a preexisting condition in the operating room (“pre” meaning before the laser was applied) and a miosis that sets in after laser treatment and thus, presumably, because of laser treatment. Poorly dilating pupils, despite intense application of topical mydriatics, usually occur in patients with comorbidities such as a hard lens, pseudoexfoliation, glaucoma, chronic uveitis, and zonular dehiscence, as well as after earlier surgery and in eyes with floppy iris syndrome. There are different ways to enlarge the pupil intraoperatively (eg, using epinephrine injection, iris retractors, or a Malyugin ring [MST, Redmond, WA], with or without ophthalmic viscosurgical devices) that we have described recently.² Adequately employed, these techniques can render femtosecond laser-assisted cataract surgery safe and effective for these patients. A narrow pupil after laser pretreatment basically means that the pharmacological dilation has been sufficient in the first place: the pupil at the beginning of the intervention has obviously been larger (usually greater than 5.0 mm) than the safety margins set for a safe capsulotomy (otherwise, the surgeon, or rather the system, would not have been able to perform accurate and safe laser pretreatment). It is these cases that have many cataract surgeons concerned, with incidences—a guess gained from conversations with other ophthalmologists—between 0% and 50%. Roberts et al. reported an incidence of 9.5% for their first 200 femtosecond laser-assisted procedures and a decrease to 1.23% in the subsequent 1,300 cases by additional instillation of a drop of 10% phenylephrine immediately after laser treatment.³ However, in our experience the incidence without the preoperative use of topical non-steroidal anti-inflammatory drugs was 5% (n = 100) and decreased to 1% (n = 100) with nonsteroidal anti-inflammatory drug pretreatment. The phenomenon of postoperative laser miosis is under evaluation; its causes are being discussed. Possible explanations are a sudden rise in the aqueous humor’s temperature immediately after the laser has been applied and the release of inflammatory mediators as a result of this temperature rise or of collateral effects of laser-induced shock waves. It seems from case reports that the more time that elapses between laser pre-treatment and the beginning of intraocular surgery, the narrower these pupils become. Experienced surgeons recommend starting lens removal no later than 15 minutes after the laser has been turned off.⁴ The ophthalmic surgical community is currently testing countermeasures such as additional epinephrine injections and viscomydriasis. Whatever the cause and whatever the cure, we should use coherent language in dealing with the problem of pupil diameters smaller than the diameter of the capsulotomy. Postoperative femtosecond laser-induced pupillary constriction seems to us to be a fitting term for all future discussions. H. Burkhard Dick, MD, PhD Ronald D. Gerste, MD Tim Schultz, MD Bochum, Germany 10.3928/1081597X-20130920-01 Dr. Dick is a member of the medical advisory board of OptiMedica, Sunnyvale, California. The remaining authors have no financial or proprietary interest in the materials presented herein. The introduction of the femtosecond laser is the latest step on the journey to refinement in cataract surgery, to ever more predictable refractive results, to a higher precision in the two crucial steps of the procedure (capsulotomy and lens fragmentation), and to higher patient satisfaction in a clientele that comes to us with the highest expectations in postoperative visual acuity. Most of us who are operating with a femtosecond laser, irrespective of which system, cannot help being astounded by the ease of the procedure and the increased safety for the patient, who is exposed to just a fraction of the ultrasound energy applied in conventional cataract surgery—and in many cases (91% of operations in one of our series)¹ to no ultrasound at all. However, there is one drop of bitterness in the chalice of femtosecond laser-assisted cataract surgery: the small pupil. If the pupil is smaller than the intended diameter of the laser-guided capsulotomy, the surgeon is in trouble. But from where do the causes of this problem arise—is it the patient or the laser? We consider it important for all cataract surgeons to use well-defined terminology to be able to discuss potential intraoperative or postoperative complications, their prevention, and their therapy—and refer to the same situation, the same challenges. First, it is obvious that we should distinguish between a small pupil as a preexisting condition in the operating room (“pre” meaning before the laser was applied) and a miosis that sets in after laser treatment and thus, presumably, because of laser treatment. Poorly dilating pupils, despite intense application of topical mydriatics, usually occur in patients with comorbidities such as a hard lens, pseudoexfoliation, glaucoma, chronic uveitis, and zonular dehiscence, as well as after earlier surgery and in eyes with floppy iris syndrome. There are different ways to enlarge the pupil intraoperatively (eg, using epinephrine injection, iris retractors, or a Malyugin ring [MST, Redmond, WA], with or without ophthalmic viscosurgical devices) that we have described recently.² Adequately employed, these techniques can render femtosecond laser-assisted cataract surgery safe and effective for these patients. A narrow pupil after laser pretreatment basically means that the pharmacological dilation has been sufficient in the first place: the pupil at the beginning of the intervention has obviously been larger (usually greater than 5.0 mm) than the safety margins set for a safe capsulotomy (otherwise, the surgeon, or rather the system, would not have been able to perform accurate and safe laser pretreatment). It is these cases that have many cataract surgeons concerned, with incidences—a guess gained from conversations with other ophthalmologists—between 0% and 50%. Roberts et al. reported an incidence of 9.5% for their first 200 femtosecond laser-assisted procedures and a decrease to 1.23% in the subsequent 1,300 cases by additional instillation of a drop of 10% phenylephrine immediately after laser treatment.³ However, in our experience the incidence without the preoperative use of topical non-steroidal anti-inflammatory drugs was 5% (n = 100) and decreased to 1% (n = 100) with nonsteroidal anti-inflammatory drug pretreatment. The phenomenon of postoperative laser miosis is under evaluation; its causes are being discussed. Possible explanations are a sudden rise in the aqueous humor’s temperature immediately after the laser has been applied and the release of inflammatory mediators as a result of this temperature rise or of collateral effects of laser-induced shock waves. It seems from case reports that the more time that elapses between laser pre-treatment and the beginning of intraocular surgery, the narrower these pupils become. Experienced surgeons recommend starting lens removal no later than 15 minutes after the laser has been turned off.⁴ The ophthalmic surgical community is currently testing countermeasures such as additional epinephrine injections and viscomydriasis. Whatever the cause and whatever the cure, we should use coherent language in dealing with the problem of pupil diameters smaller than the diameter of the capsulotomy. Postoperative femtosecond laser-induced pupillary constriction seems to us to be a fitting term for all future discussions. H. Burkhard Dick, MD, PhD Ronald D. Gerste, MD Tim Schultz, MD Bochum, Germany