Purpose
To study the correlation between posterior capsule opacification (PCO) and intraocular straylight and visual acuity.
Design
Prospective noninterventional study.
Methods
We measured visual acuity (VA), logarithm of minimal angle of resolution (logMAR) and intraocular straylight (C-Quant straylight parameter log[s]) under photopic conditions before and 2 weeks after YAG capsulotomy in 41 patients (53 eyes) from the Centro de Oftalmología Barraquer in Barcelona and the University Eye Clinic, Paracelsus Medical University in Salzburg. Photopic pupil diameter was also measured. To document the level of opacification, pupils were dilated and photographs were taken with a slit lamp, using retroillumination and the reflected light of a wide slit beam at an angle of 45 degrees. PCO was subjectively graded on a scale of 0 to 10 and using the POCOman system. A multiple regression analysis was performed to evaluate factors that influence straylight after capsulotomy.
Results
Straylight correlated well with retroillumination and reflected-light PCO scores, whereas VA only correlated with retroillumination. Both VA and straylight improved after capsulotomy. Straylight values varied widely after capsulotomy. Multiple regression analysis showed that older age, large ocular axial length, hydrophobic acrylic intraocular lenses (IOLs), and small capsulotomies are factors that increased intraocular straylight.
Conclusion
Intraocular straylight is a useful tool in the assessment of PCO. It correlates well with PCO severity scoring methods. When performing a posterior capsulotomy, factors such as age, IOL material, axial length, and capsulotomy size must be taken into consideration, as they influence intraocular straylight.
Posterior capsular opacification (PCO) is still the most frequent long-term complication after extracapsular cataract extraction surgery. The decision to perform a posterior capsulotomy is usually based on decreased visual acuity and patients’ general complaints about glare phenomena and reduced contrast. Different tests such as low-contrast acuity and acuity under glare have been used to assess glare sensitivity, but they are still not widely accepted and their validity and sensitivity are debated. Recently, intraocular straylight has been found to have added value in describing visual function, given that it is affected independently of visual acuity and contrast sensitivity. Straylight causes a veiling luminance on the retina, which can be perceived as halos, glare, hazy vision, and blinding at night while driving. The C-Quant instrument (Oculus GmbH, Wetzlar, Germany) has been demonstrated to be reliable in measuring intraocular straylight.
In an earlier study, Hayashi and associates found that visual acuity correlates more significantly with PCO than contrast sensitivity and glare sensitivity, measured with a contrast glare tester. By contrast, Meacock and associates reached the conclusion that straylight is the most sensitive test for assessing PCO severity compared with high- and low-contrast visual acuity and contrast sensitivity. A later study in European drivers showed large variations in straylight values in pseudophakic eyes, ranging from values below the normal noncataract phakic eyes to values well above. This study raised the question of whether PCO severity explains this phenomenon. Van Bree and associates found that some patients had little or no improvement in straylight after performing a posterior capsulotomy for PCO. The authors of the study suggested that PCO morphology and unknown factors other than PCO might influence retinal straylight.
The effects of pearl-type and fibrosis-type capsular opacification on visual acuity and contrast sensitivity have been studied, but there are limited data on the effect of PCO morphology on straylight. Hull and associates (Hull CC, et al. IOVS 2009;50:ARVO E-Abstract 6128) found no correlation between straylight values and PCO severity scores obtained with POCOman computer software from an in vitro PCO culture. POCOman uses retroillumination images to determine severity scores. A group of investigators found that retroillumination images might lead to underestimation of PCO, compared with slit-lamp-derived, reflected-light images. However, retroilluminated PCO images analyzed with POCOman have been compared with other computer software used to calculate PCO severity, and they proved to correlate well with high- and low-contrast acuity tests and straylight measurements.
Capsulotomy size has been associated with visual performance outcome after posterior capsulotomy. Studies have found that capsulotomies smaller than pupil size induce more sensitivity glare than larger capsulotomies. Data on the effects of monofocal and multifocal intraocular lenses (IOLs) and IOL glistenings on straylight are inconclusive.
This study compares retroillumination and reflected-light images with POCOman software for PCO assessment and evaluates their relationship with visual quality as a function of visual acuity and retinal straylight. We tried to determine the influence of various factors on straylight measurements after posterior capsulotomy.
Patients and Methods
Patients
Fifty-three eyes in 41 patients of the Centro de Oftalmología Barraquer in Barcelona (26 patients) and the University Eye Clinic, Paracelsus Medical University in Salzburg (15 patients), who were scheduled for neodymium–yttrium-aluminum-garnet (Nd:YAG) laser posterior capsulotomy from January 1, 2008 to May 31, 2009, were included in this prospective study. The mean age was 67 (range: 44 to 82).
Exclusion criteria were diabetes mellitus, glaucoma, clinical retinal or macular pathologies, optic nerve atrophy, astigmatism greater than 4 diopters, any kind of keratoplasty, and corneal opacities. Best-corrected visual acuity (VA) and straylight were measured, and photographs were taken before surgery and 2 weeks later. Pupil size was measured 2 weeks after performing the capsulotomy with the Procyon P3000 or P2000 infrared pupillometer (Procyon Instruments Ltd, London, United Kingdom).
Straylight Measurement
The C-Quant straylight meter (Oculus GmbH, Wetzlar, Germany) was used to measure retinal straylight. The measurement is based on the compensation comparison method. In short, the test field consists of a dark circle divided into 2 halves (left and right) and is surrounded by a ring-shaped flickering light, which serves as the glare source. Light emitted from the ring is scattered in the eye, resulting in the perception that the test field is flickering. A counterphase compensation light is then presented in 1 of the semicircles, reducing the flicker perception on that side. Then the patient is asked to choose the side without the compensation light (ie, the side that flickers more intensely). To obtain the straylight value, this process is repeated a set number of times with different levels of compensation light.
To ensure measurement quality, the test was repeated up to 3 times in case the computer software indicated low reliability. If the results remained unreliable, the subject was excluded from the study (n = 14). Values were expressed as log [straylight parameter] (log[s]). Higher straylight values indicate higher sensitivity to glare and thus more compromised visual function. The average normal baseline value for 20- to 30-year-old subjects is 0.90 log[s].
We considered a log[s] of 0.15 units as intrapatient variance for straylight measurements. When the difference of the straylight value after capsulotomy was > 0.15 log[s] compared with the straylight value before capsulotomy, it was considered a significant treatment effect.
Posterior Capsule Opacities Images
Pupils were pharmacologically dilated using a combination of tropicamide 0.5% and phenylephrine 2.5% topically; when fully dilated, the posterior capsule was photographed using a digital camera attached to a slit lamp. Two different images were obtained from each eye, 1 of retroillumination and 1 of the light reflected from the posterior capsule ( Figure 1 ). To obtain the reflected-light images, we used a wide slit beam at an angle of 45 degrees focused on the posterior capsule.
The corresponding photopic pupil diameter was delimited on each reflected-light and retroillumination image, and PCO inside that area was then subjectively graded on a scale of 0 to 10. Retroillumination images were also analyzed using POCOman computer software. The photopic pupil diameter was used to calculate the percentage of pupil area containing capsule remnants left from the posterior capsulotomy. Vitreous opacities visible in the reflected-light images were graded on a subjective scale of 0 to 10.
Statistical Analysis
For statistical analysis, the visual acuity decimal scale was converted into a logMAR scale. A paired t test was used to compare VA and straylight measurements before and after capsulotomy. Pearson correlation and regression coefficients (r) were calculated. A multiple regression analysis was performed. A P value of < .05 was considered statistically significant for all tests.
Results
Mean preoperative straylight measured 1.38 log[s]. It decreased on average by 0.17 log[s] units, resulting in a mean of 1.21 log[s] postoperatively. This decrease was statistically significant ( P < .001); however, 4 eyes (8%) showed an increase of more than 0.15 log[s] units ( Figures 2 and 3 ) . Postoperative straylight values varied widely; a few were above noncataract phakic eyes (9 eyes; 17%) but the majority were similar to noncataract phakic eyes (32 eyes; 60%), or similar to the normal baseline value for young subjects (12 eyes; 23%) ( Figure 4 ).
Visual acuity significantly improved ( P < .001). Mean precapsulotomy VA was 0.298 logMAR (20/40) compared with postoperative 0.078 logMAR (20/25), with a mean difference of 0.219 logMAR units. No eye lost VA after posterior capsulotomy ( Figures 2 and 3 ). Visual acuity and retinal straylight were slightly correlated prior to surgery (r = 0.399; P = .003). Two weeks after capsulotomy, these visual quality parameters had no correlation ( P = .354). Figure 5 illustrates that a gain in VA can be quite independent of straylight improvement.
When analyzing PCO images, retroillumination scoring (0-10 scale and POCOman) correlated with both VA and straylight. Reflected-light scoring (0-10 scale) correlated with straylight but not with VA ( Table 1 ).
| VA (logMAR) Post minus Pre YAG Difference | Straylight (Log[s]) Post minus Pre YAG Difference | |||
|---|---|---|---|---|
| PCO Grading | Std. Regression Coefficient ( r ) | Significance ( P ) | Std. Regression Coefficient ( r ) | Significance ( P ) |
| Reflected-light | 0.257 | .089 | 0.403 | .006 a |
| Retroillumination | 0.375 | .007 a | 0.414 | .003 a |
| POCOman | 0.460 | .001 a | 0.340 | .013 a |
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