Predicting posterior capsule opacification: Value of early retroillumination imaging

Predicting posterior capsule opacification: Value of early retroillumination imaging Lloyd E. Bender, MRCOphth, David J. Spalton, FRCOphth, William Meacock, FRCOphth, Romina Jose, PhD, James Boyce, PhD Purpose: To investigate the value of early retroillumination imaging of the posterior capsule in predicting the eventual development of posterior capsule opacification (PCO). Setting: Ophthalmology Department, St. Thomas’ Hospital, and Department of Physics, King’s College, London, United Kingdom. Methods: All patients with retroillumination images of the posterior capsule taken 6 months and 2 years after uneventful phacoemulsification with in-the-bag intraocular lens (IOL) implantation were selected. The images were taken using the same hardware and analyzed with the same software to calculate the percentage area of the posterior capsule covered by lens epithelial cells. The percentage area of PCO with all IOL types 6 months postoperatively was correlated with that at 2 years. Results: One hundred forty patients had analyzable images at 6 months and 2 years. Of these, 63 had a poly(methyl methacrylate) (PMMA) IOL (Pharmacia 812A or Storz P497UV), 33 an acrylic (Alcon AcrySof姞 MA30 or SA30), 22 a silicone (Allergan SI-30), and 22 a hydrophilic acrylic (Bausch & Lomb Hydroview姞 H60). The correlation of the percentage area of PCO at 6 months with that at 2 years resulted in an r value of 0.71 (P ⬍ .0001) in the entire group. The r value was 0.48 in the PMMA group and 0.86 in the foldable IOL group (P ⬍ .0001) (r value: AcrySof, 0.66; silicone, 0.82; Hydroview, 0.75). Conclusion: Retroillumination imaging of the posterior capsule 6 months after cataract surgery predicted the PCO outcome at 2 years in eyes with foldable IOLs. J Cataract Refract Surg 2003; 29:526 –531 © 2003 ASCRS and ESCRS

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osterior capsule opacification (PCO) is the most common complication of cataract extraction and intraocular lens (IOL) implantation, with a reported incidence between 25% and 50%.1,2 With this loss in visual acuity comes a loss of independence and further reliance on community support. Accepted for publication May 28, 2002. From St. Thomas’ Hospital (Bender, Spalton, Meacock) and the Department of Physics, Kings College (Jose, Boyce), London, United Kingdom. Presented at the Symposium on Cataract, IOL and Refractive Surgery, San Diego, California, USA, April 2001. Reprint requests to D.J. Spalton, FRCOphth, Ophthalmology Department, St. Thomas’ Hospital, Lambeth Palace Road, London SE7 1EH, United Kingdom. © 2003 ASCRS and ESCRS Published by Elsevier Science Inc.

The treatment for PCO, neodymium:YAG (Nd: YAG) laser capsulotomy, is a major expense to health care organizations in the developed world, accounting for $250 million spent by Medicare in the United States in 1993.3,4 Although Nd:YAG laser capsulotomy is a relatively simple procedure, it is not without complications including raised intraocular pressure, cystoid macular edema, retinal detachment, and damage to the IOL optic.5– 8 Many patients are now discharged from ophthalmic care within a few weeks of surgery, and there are practical difficulties in identifying those who may not realize that later visual deterioration has a treatable cause. In developing countries, where Nd:YAG laser capsulotomy is not freely available, decreasing visual acuity from PCO 0886-3350/03/$–see front matter doi:10.1016/S0886-3350(02)01641-3

EARLY RETROILLUMINATION IMAGING TO PREDICT PCO

after IOL implantation continues to be a major problem. Modern small-incision cataract surgery techniques combined with advances in IOL material and design have resulted in a decreased incidence and severity of PCO.9 –11 The quest continues to further identify factors that affect the development and progression of PCO and to modify these factors. However, it often takes 2 to 3 years before the clinical effects of PCO are apparent; thus, clinical studies require lengthy follow-up. A reduction in follow-up time would reduce the cost of research and the burden on patients and investigators. This study investigated the value of early (6-month postoperative) retroillumination images of the posterior capsule in predicting the presence of PCO at 2 years.

Patients and Methods A dedicated digital camera system was used to obtain high-resolution (25 000 pixels/mm2) retroilluminated images of the posterior capsule12 that were analyzed with customized software to determine the percentage area of PCO.13 All patients who had uneventful phacoemulsification cataract extraction, confirmed in-the-bag IOL implantation, and posterior capsule images taken 6 months and 2 years postoperatively were selected from the archives and retrospectively reviewed. The surgery was performed by 2 surgeons at St. Thomas’ Hospital between February 1996 and November 1998. All images were captured with the same hardware and analyzed by the same software protocol to calculate the percentage area of PCO within the capsulorhexis. Pearson correlation coefficients were calculated comparing the percentage area of PCO at 6 months with that at 2 years. Paired t tests were used in each IOL group to compare the difference between the 6-month and 2-year PCO values.

optic), silicone (Allergan SI-30 with a 6.0 mm disk optic and polypropylene haptics), and hydrophilic acrylic (Bausch & Lomb Hydroview威 H60 with a 6.0 mm disk optic). The PMMA group was subdivided into those with the capsulorhexis edge on the anterior IOL optic surface and those with the capsulorhexis edge off the surface (Table 1). The correlation coefficient between the 6-month and 2-year percentage PCO for the entire group was 0.71 (Figure 1). The correlation coefficients ranged from 0.48 in the PMMA group to 0.82 in the silicone group (Table 2). The correlation coefficient in the foldable IOL group (AcrySof, Hydroview, silicone) was 0.86 (Figure 2). The difference between the 6-month and 2-year PCO values was statistically significant for all except the silicone and Hydroview groups (Figure 3). In the PMMA group, the r value in the 5.5 mm optic groups with the capsulorhexis on and off the anterior IOL optic surface was 0.24 and 0.38, respectively. There was no statistically significant difference between the 6-month and 2-year percentage PCO values in the 2 groups. The correlation coefficient in the 5.5 mm and 6.0 mm optic diameter PMMA IOL groups was 0.53 and 0.51, respectively. There was no significant difference between the 6-month and 2-year PCO values in the 5.5 mm optic diameter group; however, there was a statistically significant difference between the 2 time points in the 6.0 mm optic diameter group (P ⫽ .0076).

Table 1. Characteristics of the IOLs.

IOL Type/Model

Results

Optic Diameter (mm) Manufacturer Number

PMMA

One hundred fifty-six patients had images taken 6 months and 2 years postoperatively. Of these, 13 were excluded because of poor image quality, 2 for uncertain image data, and 1 because of Nd:YAG capsulotomy. Thus, 140 patients with 6-month and 2-year images were included in the analysis. Six IOLs of 4 materials were included: poly(methyl methacrylate) (PMMA) with a disk optic (Pharmacia 812A, 1-piece with a 5.5 mm disk optic; Storz P497UV, 1-piece with a 6.0 mm optic), acrylic (Alcon AcrySof威 3-piece MA30 and 1-piece SA30, both with a 5.0 mm

812A (capsulorhexis off)

5.5

Pharmacia

24

812A (capsulorhexis on)

5.5

Pharmacia

17

P497UV

6.0

Storz

22

MA30

5.5

Alcon

17

SA30

5.5

Alcon

16

Silicone

6.0

Allergan

22

6.0

Bausch & Lomb

22

AcrySof

SI-30 Hydroview H60

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Figure 1. (Bender) Percentage PCO for all IOLs at 6 months and

Figure 2. (Bender) Percentage PCO for foldable IOLs at 6 months

2 years.

and 2 years.

The r value in the 1-piece and 3-piece AcrySof groups was 0.48 and 0.86, respectively. Table 3 shows the mean percentage area of PCO by IOL model.

sular bag retards this process and reduces the amount of PCO in vivo.16 Using a high-resolution image-capture system, we can visualize early LEC coverage of the posterior capsule within weeks of surgery. Subsequent metaplasia, fibrosis, and wrinkling result in clinically evident PCO many months later. By 6 months postoperatively, this is easily discernible, which is the reason we chose this time to take the initial images. Our data show a good correlation between the percentage area of the posterior capsule covered by LECs at 6 months and 2 years. The overall r value of 0.71 in the 4 IOL groups indicates a significant relationship between the percentage area of PCO at the 2 time points; however, there were important differences among the

Discussion The onset of PCO is a gradual and multifactorial process. Individual patient factors, surgical technique, and IOL design and material are important factors in its pathogenesis. In vitro experiments with human capsular bags and cultured lens epithelial cells (LECs) show that LEC migration and proliferation occur early, with coverage of the entire posterior capsule in vitro within days of surgery.14,15 The implantation of an IOL in the cap-

Table 2. The r values for the 6-month percentage area of PCO versus the 2-year percentage area of PCO. IOL Value

All

PMMA

AcrySof

Silicone

Number of patients

140

63

33

22

22

77

0.71

0.48

0.66

0.82

0.75

0.86

r value

Hydroview

Foldable

P value

⬍.0001

⬍.0001

⬍.0001

⬍.0001

⬍.0001

⬍.0001

95% CI

0.61-0.78

0.27-0.65

0.41-0.82

0.60-0.92

0.49-0.89

0.78-0.91

CI ⫽ confidence interval

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Figure 3. (Bender) Difference between percentage PCO at 6 months and 2 years.

types of IOLs. With an r value of 0.48, the PMMA group showed the weakest correlation. We evaluated the surgical and IOL design differences within the PMMA group to see whether these accounted for the variation. Hollick and coauthors10 report that PCO increases if the capsulorhexis is larger than the IOL diameter, a finding confirmed by other authors.17 In our study, the r value in the PMMA groups with the capsulorhexis edge on and off the anterior IOL surface was 0.24 and 0.38, respectively. A more recent study18 found that the IOL optic size affects the development of PCO, with larger Table 3. Mean percentage area of PCO by IOL group. Mean % PCO 6 Months (95% CL)

2 Years (95% CL)

Pharmacia 812A (capsulorhexis off)

63.5 (53.1-73.9)

64.4 (57.2-71.6)

Pharmacia 812A (capsulorhexis on)

21.9 (10.0-33.8)

32.9 (15.1-50.7)

All 5.5 mm optic

46.2 (36.3-56.2)

51.4 (42.0-60.8)

Storz P497UV

27.2 (20.7-33.8)

45.5 (30.6-60.4)

IOL Type/Model PMMA

AcrySof MA30

10.5 (1.7-19.2)

17.8 (7.1-28.6)

SA30

6.2 (3.4-8.9)

18.4 (6.6-30.2)

15.3 (7.9-22.6)

17.8 (9.4-26.1)

65.0 (52.6-77.3)

62.2 (51.4-73.0)

Silicone Allergan SI-30 Hydroview H60 CL ⫽ confidence limit

optic diameters resulting in significantly less PCO. Neither factor influenced the predictability of our 2-year PCO outcome. Differences in IOLs undoubtedly played an important role in the different patterns of PCO development among the various IOL groups; however, we believe the poor correlation with these IOLs is also likely related to the PMMA material itself.19 The AcrySof was the only other group with differences in IOL design. Analysis of the 1-piece and 3-piece AcrySof IOL groups showed a stronger correlation between the 6-month and 2-year PCO values in the 3-piece IOL group (r ⫽ 0.86) than in the 1-piece group (r ⫽ 0.48). This suggests that the 3-piece group had a more predictive pattern of PCO progression than the 1-piece group, although the number of patients in each group was relatively small. The pathological basis for the evidence of PCO predictability is interesting. Examination of our sequential images suggests that LECs migrate onto the posterior capsule within a few weeks of surgery and then gradually hypertrophy and thicken to produce the clinical changes seen with PCO without necessarily expanding the area (Figure 4). Thus, although the severity of PCO increases with time, the area of LEC invasion remains relatively static. Our imaging system has a reproducibility of ⫾10%, mostly because of changes in the focus of the image. The system has a very shallow depth of focus, and small differences in focus can alter the appearance of PCO between images. A number of patients in all lens groups showed low PCO values at 6 months and higher levels of PCO at 2 years (Figure 5). This could be the result of an increase in the area of LEC migration after 6 months postoperatively. Alternatively, it is possible that in some patients, a very thin, uniform layer of LECs was present at 6 months that was not detected on retroillumination imaging. Another group of patients in all IOL groups had a higher percentage of PCO at 6 months and a decrease at 2 years. In most patients, this is accounted for by changes in image quality; however, in others, it may represent LEC regression after 6 months postoperatively, a phenomenon that has been demonstrated in previous studies (Figure 6).20,21 Allowing for individual patient and technical variation and assuming that phacoemulsification surgical techniques are used, we conclude from this study that for group data, the area of LEC invasion 6 months post-

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Figure 4. (Bender) The percentage area of PCO at 6 months (left) and 2 years (right). There is no difference between the 2 time periods.

Figure 5. (Bender) The percentage area of PCO at 6 months (left) and 2 years (right). The area of PCO has increased.

Figure 6. (Bender) The percentage area of PCO at 6 months (left) and 2 years (right). There is evidence of regression of the PCO. 530

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operatively is a good indication of the degree of PCO likely to be present at 2 years. Intraocular lens material appears to be influential as the predictability was poorer for rigid PMMA IOLs than for foldable IOLs. These results suggest that poor PCO performance can be detected for an IOL by 6 months after surgery, although good performance at this time may not necessarily mean the converse. This may encourage earlier intervention if the PCO outcome is expected to be poor as well as a more goal-orientated approach to patient follow-up after cataract surgery.

11.

12.

13.

14.

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