Purpose
To determine changes in straylight after iris-fixated phakic intraocular lens implantation (pIOL) and to investigate the relationship between straylight and several preoperative and postoperative variables.
Design
Institutional, prospective cross-sectional study.
Methods
Artiflex (Ophtec B.V.) pIOL implantation was performed in 61 eyes (36 patients). Straylight values were measured before surgery and 3 months after surgery using the Oculus C-Quant (Oculus Optikgeräte). Furthermore, correlations were analyzed between straylight and the following parameters: keratometry, axial length, spherical equivalent, astigmatism, pIOL power, best spectacle-corrected visual acuity, and pupil size.
Results
Mean straylight decreased from 1.18 ± 0.17 log units before surgery to 1.13 ± 0.17 after surgery ( P = .016). Higher preoperative straylight values were associated with larger postoperative decreases in straylight ( r = −0.534; P < .001). Higher postoperative straylight values were correlated to higher axial length ( r = 0.444; P = .001) and lower keratometry values in diopters ( r = −0.414; P = .001). After regression analysis, only axial length was found to be an independent predictor of preoperative and postoperative straylight ( P < .001 and P = .001, respectively). After correcting for the axial length of an emmetropic eye (23.44 mm), all straylight correlations disappeared, indicating that an increase in distance from cornea to retina explains the increase in straylight values in longer eyes.
Conclusions
Retinal straylight was reduced significantly after Artiflex pIOL implantation. Besides age, axial length was the only predictor of preoperative and postoperative straylight values. The increased tissue length light has to pass from cornea to retina, might explain the increase in straylight values in longer eyes.
Part of the light entering the eye is scattered by imperfections of the optical media, creating a veil of light over the retina that reduces the contrast of the retinal image. This mechanism, known as retinal straylight, is present in every eye and can have several sources (eg, cornea, iris, sclera, crystalline lens, and retina). Furthermore, several individual factors such as increasing age and light iris color can lead to an increase of retinal straylight. An increase in ocular straylight can lead to glare symptoms and can reduce contrast sensitivity, affecting the quality of vision.
Recent studies have shown that some ocular pathologic features, for example, cataract, corneal edema, corneal endothelial dystrophies, and human interventions such as contact lens wear and laser refractive surgery, effect retinal straylight. A study by Rozema and associates showed that laser-assisted subepithelial keratectomy (LASEK) treatment resulted in a significant decrease of straylight values. They hypothesized that this reduction in straylight may be caused by the discontinuation of contact lens wear. Another known refractive procedure resulting in spectacle and contact lens independence is the implantation of phakic intraocular lenses (pIOLs).
Iris-fixated pIOLs currently are used for the correction of moderate to high myopia, hyperopia, and astigmatism. They have been implanted in otherwise healthy eyes since 1986, when the first iris-fixated lens was implanted in a phakic myopic eye. In 1991, the original biconcave Worst myopia claw lens was changed into a convex–concave shape and in 1998, the name of the lens changed to the Artisan lens (Ophtec B.V., Groningen, The Netherlands). In 2003, the foldable iris-fixated Artiflex pIOL (Ophtec B.V.) became available. This Artiflex lens, now used worldwide, may offer an advantage over the Artisan lens because it can be inserted through a smaller incision, which results in a decreased surgically induced astigmatism and a faster visual recovery.
We are unaware of previous reports of the influence of pIOLs on ocular straylight and could find no reference of it in a computerized search (PubMed; May 23, 2011). However, there are studies reporting and evaluating subjective reports of glare and halos after pIOL implantation. Maroccos and associates reported significantly less glare and halo problems after Artisan pIOL implantation when compared with angle-supported and posterior chamber pIOLs. However, Tahzib and associates found bothersome glare reports in 44.1% of patients after Artisan pIOL implantation, with more glare reports in patients with larger scotopic pupil sizes. All previous studies used questionnaires to classify glare and halo reports. Vilaseca and associates used an instrument called the Optical Quality Analysis System (Visiometrics SL, Terrassa, Spain), which is based on a double-pass technique using infrared light, in patients before and after Artisan or Artiflex implantation. They reported a decreased optical quality 1 day after Artisan implantation (50% to 60% loss), most likely because of a large incision and the presence of sutures. The Artiflex lens caused a much lower decrease in optical quality (20% to 25% loss). The purpose of this study was to quantify the changes in ocular straylight after Artiflex pIOL implantation and to investigate correlations between (baseline and age-corrected) straylight and several preoperative and postoperative variables.
Methods
This prospective, observational study included 61 consecutive eyes of 36 patients who received Artiflex myopia (n = 42) or Artiflex toric (n = 19) pIOLs between June 2007 and June 2009 at the Academic Center for Refractive Surgery, University Eye Clinic Maastricht, Maastricht, The Netherlands. Thirteen men and 23 women were included (toric group, 4 men and 7 women; myopia group, 9 men and 16 women), with a mean age of 40.0 ± 10.5 years.
The surgical procedures were performed by the same surgeon (R.M.M.A.N.). The surgical technique of pIOL implantation and postoperative eye drops regimen has been described elsewhere. The criteria for performing pIOL implantation in our institution are: a stable refractive error during the previous 2 years; an anterior chamber depth of 3.2 mm or more (measured from the epithelium to the crystalline lens); pupil (in mesopic light conditions) less than 7 mm; endothelial cell density 2000 cells/mm 2 or more; no corneal, pupil, or iris abnormalities; and no history of glaucoma or of chronic or recurrent uveitis.
Before surgery and 3 months after surgery undilated retinal straylight was measured using the compensation comparison-based C-Quant straylight meter (Oculus Optikgeräte, Wetzlar, Germany). The subject fixates 2 disc-shaped fields in the center and has to decide for each stimulus which of these test fields has the strongest flickering. In this way, the amount of straylight can be quantified for the examined eye.
Preoperative and postoperative straylight values were compared. To ensure a reliable straylight value, the built-in reliability parameters were chosen as follows: expected standard deviation less than 0.08 and the shape factor Q of more than 1.0, which is defined as a reliable measurement by the manufacturer. If needed, the measurement was repeated until 2 reliable measurements were obtained. The mean of 2 measurements was used for statistical analysis. Each measurement was made using the spherical equivalent correction of the patient, which can be inserted in the optical tube of the Oculus C-Quant using a set of trial lenses provided by the manufacturer. All measurements were performed under the same ambient light conditions.
During the preoperative and postoperative visit, several examinations were performed, including: subjective refraction to evaluate spherical equivalent (SE) and astigmatism, measurement of Snellen best spectacle-corrected visual acuity (BSCVA), corneal topography (EyeMap EH-290; Alcon, Fort Worth, Texas, USA) to evaluate the keratometry values, axial length (IOLMaster; Carl Zeiss Meditec, Dublin, California, USA), and pupil size in mesopic low lighting conditions (P2000 SA pupillometer; Procyon Instruments Ltd, London, United Kingdom).
Statistical Analysis
All collected data were exported from an Excel spreadsheet (Microsoft, Redmond, Washington, USA) to SPSS for Windows software version 15.0 (SPSS, Inc, Chicago, Illinois, USA) for data analysis. Continuous variables were described as mean ± standard deviation. Straylight values were measured by the Oculus C-Quant on a logarithmic scale (log(s)). To compare the preoperative and postoperative measurements, paired t tests were applied. Straylight also was compared with a normal reference data base to calculate the base and age-corrected straylight value. We used the method as described in the study by Rozema and associates. In healthy eyes, retinal straylight can be modelled using the following equation:
To calculate the base and age-corrected straylight value, the measured straylight values were subtracted by the above-mentioned reference model (1).
Besides the influence of age, Rozema and associates described an increase of straylight with higher axial length. Therefore, we designed a model to correct for the axial length of a normal population ( L norm = 23.44 mm), computing the base, age and axial length-corrected straylight value, using the following equation:
log ( s ) = [ 0 ⋅ 931 + log ( 1 + ( A g e / 65 4 ) ] × [ 1 + ( a x i a l l e n g t h − L n o r m ) / L n o r m ] , L n o r m = 23.44.
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