Ординатура / Офтальмология / Английские материалы / Modern Cataract Surgery_Kohnen_2002

Fig. 1. Image analysis system (EPCO) for evaluation of PCO behind the IOL.

values were calculated by multiplying the area of opacification of the IOL optic (0–100% 0–1.0) with a graduated PCO value (0–4).

Statistical analysis was performed calculating mean values, standard deviation, analysis of variance and Kruskall-Wallis analysis of variance for nonparametric data using Microsoft Excel 4.0 and Systat 5.03 for Windows™.

Results

Twenty-four patients could be examined 4 years postoperatively (14 PFC, 10 controls). Both patient groups did not show any differences in terms of mean age or postoperative follow-up and corrected distance acuity (fig. 2, 3, table 1). The PCO value increased from 0.31 in the first year after implantation to 1.5 after 46 months (PFC-IOL) and from 0.31 to 1.2 (standard PMMA-IOL), respectively (fig. 4–6).

Both IOLs showed no significant difference referring to the PCO expression at any examination time (table 1, fig. 4–6). PCO values after 4 years showed a great range between 0 and 3.6 for both groups (fig. 6). A Nd:YAG capsulotomy

Fig. 2. Development of visual acuity over 4 years.

1

0.5

Visual acuity

0.1

Fig. 3. Mean visual acuity in both patient groups.

was performed in 2 of 14 patients with PFC-IOL and in 1 of 10 patients with standard PMMS-IOL.

Discussion

PCO is the important long-term complication after extracapsular cataract extraction with implantation of a posterior chamber lens [1, 2, 4]. In the literature,

Table 1. Patient data

Fig. 4. Development of PCO 4 years after implantation.

development of PCO after an extracapsular technique varies from 3 to 50% 2–5 years after implantation [2, 5, 9–17]. Reasons for different frequencies of PCO development depend for example on different observation times and different age distributions of the evaluated patient groups. This could be explained by the influence of ocular, extraocular, systemic factors and different methods of PCO evaluation [18]. It is known that the implantation of a posterior chamber lens into the capsular bag reduces the expression of PCO [2, 8–13, 15, 16]. Moreover, biconvex optical design and a sufficient contact between the optic and posterior part of the capsular bag decrease the development of PCO [2, 9–13, 15, 16].

In this long-term study an examiner-independent, standardized PCO evaluation method developed by Tetz et al. [18] was used to analyze the influence of PFC surface modification on PCO development (fig. 1). Both patient groups

Fig. 5. Mean values of PCO 4 years after cataract extraction. Difference between PFCIOL group and standard PMMA-IOL group was not statistically significant (p 0.58, Mann-Whitney U test).

PCO value (area density)

Fig. 6. PCO values 4 years after cataract extraction. PCO values of the PFC-IOL group and standard PMMA-IOL group show a similar range from 0 to 3.6.

could be compared because they did not show any differences in terms of mean age, follow-up time or systemic conditions which could influence the expression of PCO, like diabetes mellitus [17], pseudoexfoliation syndrome [6], retinitis pigmentosa [19] and so on.

Patients with PFC-IOLs presented with equal functional results compared to those with standard PMMA-IOL. A difference in PCO formation could not be detected between the groups. The low rate of capsulotomy can be explained by the good acuity of vision from 0.6 to 0.7. A specific coating of IOL with equal

optical-functional results which reduces the PCO development would be an elegant solution for the PCO problem. PFC-coated optical surfaces could not help decrease the rate of PCO in this study.

References

1Apple DJ, Kincaid MC, Mamalis N, Olson RJ: Intraocular Lenses. Evolution, Designs, Complications, and Pathology. Baltimore, Williams & Wilkins, 1989.

2Apple DJ, Solomon KD, Tetz MR, Assia EI, Holland EY, Legler UF, Tsai JC, Castaneda VE, Hoggatt JP, Kostick AM: Posterior capsule opacification. Surv Ophthalmol 1992;37:73–116.

3Auffarth GU, Schmidt JA, Wesendahl T, Recum AV, Apple DJ: Surface characteristics of intraocular lens implants: An evaluation using scanning electron microscopy and three-dimensional topographical profilometry. Long-Term Effects Med Implants 1993;3:321–332.

4Apple DJ, Auffarth GU, Peng Q, Visessook N: Foldable Intraocular Lenses: Evolution, Clinicopathologic Correlations and Complications. Thorofare, Slack Inc., 2000.

5Tetz M, Greiner C, Blum M, Faller U, Völcker HE: Zellbesiedlung und Hinterkapseltrübung bei Polyfluorocarbon beschichteten Hinterkammerlinsen – erste klinische Ergebnisse; in Robert YCA, Gloor B, Hartmann C, Rochels R (eds): Transactions. 7. Kongress der Deutschsprachigen Gesellschaft für Intraokularlinsen-Implantation (DGII), Zürich 1993. Berlin, Springer, 1993,

pp344–350.

6Zetterström C: Incidence of posterior capsule opacification in eyes with exfoliation syndrome and heparin-surface-modified intraocular lenses. J Cataract Refract Surg 1993;19:344–347.

7Faller U, Tetz MR, Blum M, Greiner C, Völcker HE: Endothelzellverlust bei Polyfluorocarbon beschichteten Intraokularlinsen; in Pham DT, Wollensak J, Rochels R, Hartmann C (eds): Transactions. 8. Kongress der Deutschsprachigen Gesellschaft für Intraokularlinsen-Implantation (DGII) Berlin 1994. Berlin, Springer, 1994, pp 336–339.

8Tetz MR, O’Morchoe DJC, Gwin TD, Wilbrandt TH, Solomon KD, Hansen SO, Apple DJ: Posterior capsular opacification and intraocular lens decentration. II. Experimental findings on a prototype circular intraocular lens design. J Cataract Refract Surg 1988;14:614–623.

9Born C, Ryan D: Effect of intraocular lens optic design on posterior capsular opacification. J Cataract Refract Surg 1990;16:188–192.

10Davis P, Hill P: Inhibition of capsule opacification by convex surface posterior three-piece all PMMA C-loop lenses: A fellow eye and same lens study. Eur J Implant Refract Surg 1989;1: 237–240.

11Davis PL, Hill P, Coffey A: Convex posterior PMMA implants: Do PMMA vs. prolene haptics alter capsular opacity? Eur J Implant Refract Surg 1991;3:127–130.

12Götting J, Knorz MC, Seiberth V, Münch D: Nachstarrate mit bikonvexen und konvexplanen IOLs – Eine prospektive Studie; in Wenzel M, Reim M, Freyler H, Hartmann C (eds): 5. Kongress der Deutschen Gesellschaft für Intraokularlinsen-Implantation (DGII). Berlin, Springer, 1991,

pp698–703.

13Hansen SO, Solomon KD, McKnight GT, Wilbrandt TH, Gwin TD, O’Morchoe DJ, Tetz MR, Apple DJ: Posterior capsular opacification and intraocular lens decentration. I. Comparison of various posterior chamber lens designs implanted in the rabbit model. J Cataract Refract Surg 1988;14:605–613.

14Morrell AJ, Pearce JL: Cataract surgery with posterior chamber lens implantation in patients aged 20–45. Eur J Implant Refract Surg 1989;1:85–87.

15Nishi O: Incidence of posterior capsule opacification in eyes with and without posterior chamber intraocular lenses. J Cataract Refract Surg 1986;12:519–522.

16Tetz M, Imkamp E, Hansen SO, Solomon KD, Apple DJ: Experimentelle Studie zur Hinterkapseltrübung und optischen Dezentrierung verschiedener Hinterkammerlinsen nach intrakapsulärer Implantation. Fortschr Ophthalmol 1988;85:682–688.

17Tetz MR, Lehrer I, Klein U, Völcker HE: Cataracta secundaria bei Diabetes Mellitus; in Pham DT, Wollensack J, Rochels R, Hartmann C (eds): 8. Kongress der Deutschen Gesellschaft für Intraokularlinsen-Implantation (DGII). Berlin, Springer, 1994, pp 398–406.

18Tetz MR, Auffarth GU, Sperker M, Blum M, Völcker HE: Evaluation of a photographic image analysis system for PCO scoring. J Cataract Refract Surg 1997;23:1515–1520.

19Auffarth GU, Peng Q: Posterior capsule opacification: Pathology, clinical evaluation and current means of prevention. Ophthalmic Pract 2000;18:4:172.

Gerd U. Auffarth, MD, Department of Ophthalmology, Ruprecht Karls University of Heidelberg, Im Neuenheimer Feld 400, D–69120 Heidelberg (Germany)

Tel. 49 6221 566 631, Fax 49 6221 561 726, E-Mail gerd_auffarth@med.uni-heidelberg.de

Fig. 1. Insertion of anterior piggyback

IOLs.

that accurate measurements are most difficult to obtain. Ultrasound axiometers are calibrated with average velocities for normal length eyes. These velocities are incorrect for short eyes, causing significant measurement errors [9].

Performing applanation biometry is frequently difficult in short eye cases with a shallow anterior chamber because it can be difficult to distinguish the initial ‘bang’echo from the iris and establish perpendicularity. Decreasing the ultrasound gain may be necessary when this occurs so each echo can be visualized but doing so can make the scan more difficult to perform. The most significant problem with applanation biometry is that the cornea is easily indented even in the hand of the most skilled ultrasound technician. Even the slightest indentation can cause significant measurement errors which are magnified when the eye is short [9–11].

Immersion biometry can provide superior results in these cases [12]. First, it is impossible to applanate the cornea. Thus, by its very nature, immersion is more reliable. Second, it allows visualization of the corneal echoes. In order to obtain the most accurate measurement, the skilled ultrasound technician will watch for consistency of echo height, axial length, lens thickness, and anterior chamber depth readings.

Optimizing axial length measurements does not guarantee the desired outcome. In a study one of the authors (J.P.G.) performed with Dr. Jack Holladay [9], several hyperopic patients were examined and more detailed anatomical measurements were taken. In most cases the short eye cases had normal anterior segment dimensions (corneal diameter, keratometry, and anterior segment length). The ‘abnormality’ was a foreshortened axial length due to a shortened posterior segment.

Based on these observations we can conclude that most third-generation power formulas systematically generate hyperopic errors in power calculation among most short eye cases because they shorten the expected anterior chamber depth to the lens as a function of the axial length [8]. Thus they all predict the position of the lens to be too far anterior, resulting in a hyperopic error.

Holladay [8] has reported that prediction accuracy in short eyes is significantly improved with the Holladay-2 formula, which uses extra measurements to take into account the sometimes unusual anatomy often found in high hyperopes. He reported a decrease in mean absolute error among short eye cases from about 4.5 D with other formulas to a little less than 1 D with the Holladay-2 formula. About 4% of eyes with average total axial lengths have anterior segment sizes which are large or small relative to the posterior segment and may also benefit from the use of a power formula based on more measurements.

Furthermore, when the ‘piggyback’ technique is used in high hyperopes, power calculations must be adjusted again. By measuring the distance from the iris to the IOL vertex, Holladay and Gills [9] determined that the anterior-most lens is in the usual position while the posterior-most lens is pushed back, causing additional hyperopic error. Apparently the anterior lens pushes the posterior lens further back due to the elastic nature of the capsular bag. Thus, additional power must be factored into the equation. The Holladay-2 formula provides such adjustments [8]. For these reasons, the Holladay-2 formula is the formula of choice for piggyback implantation lens power calculation. We have found improved accuracy in our piggyback cases after switching to this formula [13].

Surgical Technique

All patients undergoing cataract surgery receive a thorough explanation of the type of anesthesia to be used, what to expect during surgery, and the risks involved with surgery. This is especially important with high hyperopes since compliance during surgery is critical. Topical anesthesia can be used for these patients, just as for cases with average axial lengths. However managing complications is certainly more difficult under topical anesthesia, and high hyperopes are at greater risk for certain complications such as shallow anterior chambers; iris prolapse; pupillary block while the pupil is dilated, which can result in a hard eye; and choroidal effusion or fluid misdirection which can increase the pressure in the eye. Many surgeons may prefer regional anesthesia for these cases.

For primary piggyback cases, we use either two PMMA single-piece biconvex IOLs with an optic size of 5.5 mm, or one plate-haptic silicone lens (with the majority of the power) in the bag and one three-piece silicone lens in the sulcus (minimal power). By combining these two silicone IOLs, better centering is often obtained and there is less chance of IOL dimpling. We generally