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Sharp posterior edge design reduces PCO but may increase ACO
A SHARP posterior optic edge design can significantly reduce posterior capsule opacification (PCO) compared to similar IOLs with a round posterior edge design although the sharp-edged optics may increase anterior capsule opacification (ACO), according to the results of two related Austrian studies presented at the XXI Congress of the ESCRS. Wolf Buehl MD described the results he obtained in a prospective randomised trial involving 106 eyes of 53 cataract patients who underwent implantation of two different types of acrylic IOL that differed only in the design of the posterior edge of the optic. The patients received the round-edged AR40 in one eye and an AR40e IOL (Sensar OptiEdge, AMO) with a square posterior edge in the other eye.At three years follow-up, only one eye in the OptiEdge group required YAG capsulotomy, compared to 12 eyes in the round-edged IOL group, Dr Buehl said. In addition, eyes implanted with sharp-edged optic had significantly less PCO at one, two, and three years follow-up compared to those in the round-edged IOL group. Furthermore, PCO scores in the sharp-edged group were lower whether made subjectively by examiners at slit-lamp or objectively using digital retro-illumination images and automated image analysis software (AQUA, "Automated quantification of After-Cataract") developed in cooperation with the Technical University of Graz. Using objective measurements, the mean PCO score at one year was 0.26 for the AR40e and 1.5 for the AR40. At two years the respective scores were 0.5 and 2.0 while at three years the respective scores were 1.0 and 2.9. Using automated image analysis, the mean objective PCO scores were 0.26 and 0.92 at one year, 0.41 and 2.15 at two years and 1.2 and 2.5 at three years, respectively. Dr Buehl noted that the two groups were different with regard to only one parameter, namely the optic edge design (round edges vs. sharp posterior optic edge design). Both types of IOL are hydrophobic three-piece acrylic IOLs with an optic diameter of 6 mm and an overall length of 13 mm and a 6° angulation of the haptics. All of the patients in the study had bilateral age-related cataracts. None had ocular co-morbidities such as diabetic retinopathy or glaucoma. Rupert Menapace MD performed all of the surgeries.There was no significant difference between the two groups regarding edge glare and other optical phenomena. There was also no significant difference between the groups regarding postoperative BCVA. However, Dr Buehl pointed out that the good visual outcome among those in the round-edged IOL group was partly due to the success of YAG capsulotomies in the 12 patients who required them.
The findings of the study also highlight the usefulness and reliability of PCO measurements obtained with digital ophthalmoscopy and an automated PCO analysis program, Dr Buehl said.He noted that in a study he conducted involving 30 pseudophakic eyes with varying degrees of PCO there was a good correlation between PCO scores obtained with the automated image analysis software and subjective measurements of PCO-related visual dysfunction, both before and after YAG capsulotomy. That is, following YAG capsulotomy the mean ETDRS visual acuity improved from 0.28 to -0.07 (Log MAR scale) while the respective scores using the AQUA software were 3.56 and 0.18. The correlation coefficient between the two types of measurement was 0.72, Dr Buehl noted, adding: "The objective PCO score obtained by an automated image analysis program correlates well with the PCO-induced decrease of visual acuity. It is, therefore, a valuable measure for clinical studies on PCO prevention."In a related study, Dr Buehl's associate Stefan Sacu MD, noted that one potential side effect of reducing PCO with a modified optic edge may be a slight increase in anterior capsule opacification (ACO). The randomised prospective study involved 162 eyes of 81 patients with bilateral age-related cataract. All underwent standardised cataract surgery by the same surgeon. One group of 43 patients received acrylic IOLs with a round-edged optic IOL (AMO-AR40) in one eye and a sharp posterior edge optic (AMO-AR40e) in the contralateral eye. A second group of 38 patients received silicone IOLs with a round edge (AMO-SI40) in one eye and a sharp posterior edge (AMO-Clariflex) in the contralateral eye, Dr Sacu explained. As in Dr Buehl's study PCO scores at one year's follow-up were lower in eyes implanted with IOLs with a sharp posterior edge. That is, the fibrotic PCO scores, on a scale from 1-4, of digital slit-lamp photographs were 0.26 for eyes with the sharp edged AR40e and 0.92 for the round edged AR40. Similarly, among eyes with silicone IOLs, the mean fibrotic PCO score was 0.23 for the sharp posterior edged IOL and 1.01 for the SI40 lens (p<0.01). The opposite held true regarding ACO, however. Objective analysis showed that among eyes with acrylic implants the mean ACO was 32% for the AR40e and 29% for the AR40 (p<0.05). Similarly, among eyes with silicone IOLs the mean ACO was 31.2% for the sharp-edged optic IOL and 26.1% for the round-edged SI40 lens (p<0.05), Dr Sacu noted, adding:"Compared to the round-edged IOLs, the modified edge design of the acrylic and silicone IOLs, lead to significantly less PCO, but slightly more ACO. The sharp posterior edge inhibits migration of anterior capsule lens epithelial cells behind the optic, therefore resulting in slightly stronger ACO." Wolf Buehl MD,
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