Clinical application of the Lens Opacities Classification System III in the performance of phacoemulsification

Transcription

1 Clinical application of the Lens Opacities Classification System III in the performance of phacoemulsification James A. Davison, MD, Leo T. Chylack Jr., MD Purpose: To report the correlation of features of cataracts graded by the Lens Opacities Classification System, version III (LOCS III), with phacoemulsification energy expenditure and the balanced salt solution (BSS ) volume used during cataract surgery. Setting: Wolfe Clinic, Marshalltown, Iowa, USA. Methods: This was a retrospective review of 2364 cases operated on by a single surgeon from January 1998 to July 2000 in which the cataract had been graded at the slitlamp using the 4 grading scales of the LOCS III: nuclear opalescence (NO), nuclear color (NC), cortical cataract (C), and posterior subcapsular cataract (P). Polynomial best-fit lines were derived using regression analysis correlating the 4 preoperative LOCS III characteristics with 3 intraoperative observations: machine-measured phacoemulsification time, mean power expenditure, and BSS volume. Results: As determined by best-fit lines and their coefficient of determination (R 2 ), there were exponential relationships between machine-measured phacoemulsification time and the degree of NC (R ) and NO (R ). Trends existed between NC and NO and the amount of BSS used (R and R , respectively). No relationships were observed between the LOCS III classes of cataract, C and P, at any intraoperative observation. Conclusions: Exponentially, greater phacoemulsification energy was required as NC and NO increased. The LOCS III cataract grading system enhanced the ability to estimate ultrasonic energy expenditure and BSS volume use during phacoemulsification. Preoperative LOCS III cataract classification can help to create a more formally organized, integrated, customized operative plan. J Cataract Refract Surg 2003; 29: ASCRS and ESCRS The Lens Opacities Classification System, version III (LOCS III), is a widely used, scientifically valid, standardized photographic comparison system for grading the features of the human age-related cataract. 1 5 It has been used to grade the type and severity of cataract in Accepted for publication September 12, From the Wolfe Clinic, Marshalltown, Iowa, USA. Presented at the Symposium on Cataract, IOL and Refractive Surgery, San Diego, California, USA, April 2001 Reprint requests to James A. Davison, MD Wolfe Clinic, 309 East Church Street, Marshalltown, Iowa, USA. cross-sectional studies and the progression of cataract in longitudinal studies. It also has been used to grade cataracts at the slitlamp. 3 Grading using LOCS III involves the assessment of 4 features shown on 3 sets of photographs on an 8.5-inch 11-inch color transparency (Figure 1). The features of nuclear opacification and brunescence are graded according to 1 set of 6 photographs. The brightness of scatter from the nuclear region has been designated nuclear opalescence (NO) and the intensity of brunescence, nuclear color (NC). The amount of cortical cataract (C) is determined by comparing the estimated aggregate of cortical spoking to that seen in 2003 ASCRS and ESCRS /03/$ see front matter Published by Elsevier Science Inc. doi: /s (02)

2 Figure 1. (Davison) The LOCS III standard images in an 8.5-inch 11-inch color transparency as used in the office at the slitlamp. The top row contains the standards for NO and NC. The second row contains the standards for grading C and the bottom row, for grading P. 5 separate photographs. Similarly, the estimated amount of posterior subcapsular cataract (P) is determined by comparing it to another 5 photographs depicting increasing amounts of posterior subcapsular cataract. The grade for each feature is derived by locating the image of the patient s lens on the scale of severity for each feature represented in the color transparency. The NC and NO are graded on a decimal scale of 0.1 to 6.9. The severity of C and P are graded on a decimal scale of 0.1 to 5.9. The final LOCS III grade comprises 4 decimal values, 1 each for NO, NC, C, and P. In the original publication describing the LOCS III system, 1 an assessment of within-grader and betweengrader reproducibility was done and expressed as a 95% confidence interval for each scale. On average, these 95% confidence intervals were approximately 0.7 units. The intervals were used to define a significant change in the severity of the cataract. For example, if the NO grade was 2.3 at baseline and 1 year later it was 3.5, the increase in severity ( ) was greater than the 95% confidence interval (0.7) and it was therefore reasonable to conclude that one was 95% confident that the change was statistically significant. If the increase had been only 0.5 units, the increase could more likely be the result of the intrinsic methodologic noise of the LOCS III system and not a true increase in the severity of the cataract. Since 1998, LOCS III has been used systematically in the clinical practice of one author (J.A.D.). Preoperative LOCS III grading of all surgical patients was done at the slitlamp to improve clinical documentation in the clinical record. Parenthetical descriptions were rarely added but usually included the critical nature of the centrality within the visual axis of subtle localized interfaced zones of NO and NC, cortical spokes, or subcapsular opacities. There was consistency in grading over time, and patients could be told with greater confidence whether their cataracts were stable or progressing. It was also helpful to have accurate measures of cataract severity when discussing cases with third-party payer representatives; surgical interventional decisions to offer surgery to some patients could be better defended. Over time, LOCS III slitlamp grading was empirically incorporated into the decision-making process and planning of upcoming surgeries. Ultimately, this resulted in a more organized, integrated, customized operative plan for each patient. Patients and Methods In this retrospective study, 2364 consecutive cases of phacoemulsification were analyzed with respect to the 4 LOCS III characteristics and machine-measured phacoemulsification time, average machine measured power (%), and the balanced salt solution (BSS ) volume used. All data points had been recorded in 2186 cases. Surgery was performed from January 1998 to July 2000 by a single surgeon (J.A.D), who also performed LOCS III grading of all cataracts at the slitlamp. A standardized nuclear-fracture quadrant-aspiration phacoemulsification technique was used with a straight 45-degree 0.9 mm ABS MicroTip with the Alcon Legacy 20,000 machine. 6 After topical anesthesia was administered, a temporal clear corneal incision was made. Grooving was accomplished with the machine in memory I (phacoemulsifica- J CATARACT REFRACT SURG VOL 29, JANUARY

3 Figure 2. (Davison) After initial grooving is completed, a second rotation of the nucleus allows for improved visualization while deeper grooving progresses in hard nuclei. Figure 3. (Davison) Nuclear cracking is created from the periphery toward the center with a cross action of the phacoemulsification tip and the cyclodialysis spatula. Figure 4. (Davison) The 45-degree phacoemulsification tip is turned sideways with its aperture facing the interior wall of the first nuclear quadrant. Low levels of emulsification energy are used to engage and impale the central portion of the quadrant. Figure 5. (Davison) A low level of ultrasonic energy and a higher level of vacuum allow the tip to adhere to the softer edge of the quadrant and drag it centrally. tion power maximum, 90%; vacuum maximum, 50 mm Hg; aspiration flow rate, 14 cc/minute) (Figure 2). Wider, deeper grooves were made as nuclear hardness increased. The posterior nuclear plate was torn from the periphery toward the center by cross action with the phacoemulsification tip and a custom, modified, 0.37 mm cyclodialysis spatula (Figure 3). Quadrant aspiration was accomplished in memory III (phacoemulsification power maximum, 70%; vacuum maximum, 500 mm Hg; aspiration flow rate, 35 cc/minute). The aspiration process was kept posterior to the iris plane within the capsular bag as much as possible to protect the corneal endothelium from damage from fragment impact and abrasion (Figures 4 to 6). Sodium hyaluronate 3.0% chondroitin sulfate 4.0% (Viscoat ) was usually injected into the anterior chamber before quadrant aspiration when the NC was greater than 4.5. In some cases, Viscoat was reinjected before aspiration of the fourth quadrant because of the tendency of the capsular bag to flatten after the third quadrant had been removed, which forces the remaining process anterior to the iris plane. In some eyes, soft quadrants or the last fragment of the fourth firm quadrant were removed using reduced vacuum (maximum 300 mm Hg), maximum power 140 J CATARACT REFRACT SURG VOL 29, JANUARY 2003

4 Figure 6. (Davison) The bulk of the quadrant is central while moderate ultrasonic energy, vacuum, and aspiration flow are used to remove the firm portions of the quadrant. Figure 7. (Davison) Aspiration can begin after an edge of the last quadrant is lifted free of the posterior capsule. (50%), and a reduced aspiration flow rate (25 cc/minute) (Figures 7 and 8). Polynomial best-fit lines were derived by regression analysis among the 4 LOCS III characteristics and the 3 phacoemulsification observations. Figure 8. (Davison) The cyclodialysis spatula protects the posterior capsule as phacoemulsification power is applied during removal of the last quadrant. Lower levels of vacuum and aspiration flow rate help protect the posterior capsule from inadvertent aspiration. Table 1. Scale Range Mean machine-measured ultrasound time (minutes). LOCS III NO Scale LOCS III NC Scale Total NO nuclear opalescence; NC nuclear color Results The mean machine-measured phacoemulsification time increased as the NO and NC grades increased (Table 1). As determined by the best-fit lines and their coefficients of determination (R 2 ), there was an exponential relationship between NO and machine-measured phacoemulsification time (R ). A trend existed between NO and the mean power (R ) and the amount of BSS used (R ) (Figure 9). A slightly stronger exponential relationship existed between NC and machine-measured phacoemulsification time (R ). A trend also existed between NC and mean power (R ) and the amount of BSS used (R ) (Figure 10). No relationships were observed between the LOCS III classes of cataract, C and P, and any intraoperative observation (Figures 11 and 12). Discussion In the original LOCS III publication, the NO and NC scales were highly correlated with each other and the relationships between objective measures of NO, NC, and the LOCS III grade of the standard images were J CATARACT REFRACT SURG VOL 29, JANUARY

5 Figure 9. (Davison) A significant relationship is seen between LOCS III NO and ultrasound time but not mean ultrasound power and BSS volume used. Figure 10. (Davison) A significant relationship is seen between LOCS III NC and ultrasound time but not mean ultrasound power and BSS volume used. 142 J CATARACT REFRACT SURG VOL 29, JANUARY 2003

6 Figure 11. (Davison) No relationship is seen between LOCS III C and ultrasound time, mean ultrasound power, and BSS volume used. Figure 12. (Davison) No relationship is seen between LOCS III P and ultrasound time, mean ultrasound power, and BSS volume used. J CATARACT REFRACT SURG VOL 29, JANUARY

7 nearly linear. The NO was assessed independently with image analysis of optical density, and NC was assessed independently with fast spectral scanning colorimetry of each LOCS III standardized image. Highly different grades of NO and NC in the same cataract were unlikely. Similarly, the relationship between the expenditure of phacoemulsification energy and the LOCS III grades of NO and NC appears to be linear for LOCS III grades below approximately 3.7. Above that, the relationship between LOCS III grade and phacoemulsification energy expenditure seems to become exponential. Although in LOCS III NO and NC are graded separately, most clinicians are accustomed to describing nuclear change by a single term, nuclear sclerosis. Both color change and increased light scattering are part of the process of nuclear sclerosis, and it is therefore not surprising to have found that both NO and NC are similarly positively correlated with ultrasonic energy exposure. When viewing a cataractous lens with LOCS III NO and NC grades of 4.0 to 5.0, most surgeons intuitively anticipate increased phacoemulsification times. The nucleus is simply harder, so it will take more energy to emulsify. The LOCS III NC grade has been correlated with hardness of the central nucleus as measured by the resistance to a fine conical probe measured by a dynamometer. 7 Phacoemulsification energy recorded by cumulative delivered energy as well as by postoperative anterior chamber flare has been shown to be correlated with LOCS III NC and NO. 8 The surgeon in this study finds it useful to be able to accurately grade opalescence and brunescence (and the severity of C and P) to better estimate when prolonged ultrasonic time or increased ultrasonic energy is likely. It has proved advantageous to integrate LOCS III grading into routine operative planning. By doing so, the surgeon will be better prepared to manage the more sclerotic nucleus and his or her preoperative planning can be more patient specific. The surgeon in this study empirically formulated several recommendations for customizing a surgical plan using preoperative LOCS III grading as a part of a complete preoperative ophthalmic examination. These are listed below. 1. A retentive viscoelastic material is recommended in cases in which the LOCS III NO or NC grade is 4.0 or greater. 2. If the LOCS III NO or NC grade is 5.0, the capsulorhexis will be more easily visualized if indocyanine green dye is used to stain the anterior capsule. 3. If the pupil is smaller than 4.5 mm and the LOCS III NO or NC grade is greater than 4.5, use of a pupil expansion/maintenance device should be considered. 4. If zonular integrity is compromised and the LOCS III NO or NC grade is 4.5 or greater, a backup ciliary-sulcus-supported intraocular lens (IOL) or anterior chamber IOL should be available. 5. Surgeons in training should learn and use LOCS III grading to enable them to select normal cases with nuclei of enough substance to easily manipulate yet readily emulsify. Very soft or very hard nuclei may present unnecessary challenges. 6. The LOCS III is helpful and should be used in the trials of new technologies for cataract removal. For example, in one author s experience (J.A.D.) with early AquaLase technology (Alcon Surgical), efficient removal of a nucleus with an NC grade greater than 3.7 was not possible. Of course, the relationships between LOCS III characteristics and phacoemulsification energy expenditure vary with the individual technique and equipment used. Despite this individual-specific variation, it is likely that the trends observed will be seen with other surgeons as long as a mechanical removal technique is used. Incorporating LOCS III grading into a preoperative regimen should not only improve surgical planning, it should also improve clinical documentation, communication among providers and with third-party payers, and the accuracy of longitudinal follow-up. Most important, preoperative LOCS III classification should contribute to more predictable and effective cataract surgery. References 1. Chylack LT Jr, Wolfe JK, Singer DM, et al. The Lens Opacities Classification System III; the Longitudinal Study of Cataract Study Group. Arch Ophthalmol 1993; 111: Maraini G, Pasquini P, Tomba MC, et al. An independent evaluation of the Lens Opacities Classification System II (LOCS II); the Italian-American Cataract Study Group Ophthalmology 1989; 96: Karbassi M, Khu PM, Singer DM, Chylack LT Jr. Evalu- 144 J CATARACT REFRACT SURG VOL 29, JANUARY 2003

8 ation of Lens Opacities Classification System III applied at the slitlamp. Optom Vis Sci 1993; 70: Milton RD, Chylack LT Jr, Köpcke W. Letters to the editor. Ophthalmic Epidemiol 1996; 3: van den Berg TJTP, Coppens JC. Conversion of lens slit lamp photographs into physical light-scattering units. Invest Ophthalmol Vis Sci 1999; 40: Davison JA. Performance comparison of the Alcon Legacy mm TurboSonics and 0.9 mm Aspiration Bypass System tips. J Cataract Refract Surg 1999; 25: Hu C, Zhang X, Hui Y, Chung H. [The nuclear hardness and associated factors of age-related cataract]. [Chinese] Yen Ko Tsa Chih 2000; 36: Ursell PG, Spalton DJ, Tilling K. Relation between postoperative blood-aqueous barrier damage and LOCS III cataract gradings following routine phacoemulsification surgery. Br J Ophthalmol 1997; 81: J CATARACT REFRACT SURG VOL 29, JANUARY