Straylight Meter Research Articles

Characteristics of straylight after small incision lenticule extraction versus femtosecond laser-assisted laser in situ keratomileusis

Background Small incision lenticule extraction (SMILE) was a new procedure which is mini-invasion and flapless,but few attentions were paid to the visual quality after SMILE.To understand the changes of intraocular straylight after SMILE is of important significance for the assession of the visual quality after the procedure. Objective This study was to compare the characteristic of straylight between SMILE and femtosecond laser assisted laser in situ keratomileusis (FS-LAISK) after surgery. Methods A retrospective study was designed.Written informed consent was obtained from each patient prior to accepting the surgery.One hundred and twenty-seven eyes of 68 patients with myopia and myopic astigmatism were included in Tianjin Eye Hospital from January 2011 to July 2013.SMILE was performed on 64 eyes of 35 patients and FS-LASIK was carried out in 63 eyes of 33 patients at the same period.Stray light was detected with C-Quant stray light meter before and 1 week,1 month and 6 months after surgery.The changes of stray light values following the surgery were compared between the two groups,and the correlations between postoperative stray light values with operative parameters were analyzed. Results The mean stray light values were (1.03±0.19)D and (0.95±0.16)D at 1 week and 1 month after surgery,which were higher than (0.88±0.18)D at preoperation in the FS-LASIK group (P=0.000,0.012).The stray light values were (0.98±0.16),(0.95±0.14) and (0.94±0.16)D at 1 week,1 month or 6 months after surgery,and no statistically significant differences were found in comparison with (0.91±0.15)D in preoperation in the SMILE group (all at P>0.05).No significant intergroup difference was seen in the stray light values (Fgroup=0.077,P=0.781).The stray light differences of various time points after surgery and before surgery were increased in the FS-LASIK group compared with SMILE group (Fgroup=14.798,P<0.001),with the significant difference in postoperative 1 week between the two groups (P<0.01).The negative correlations were found between stray light values at 1 week,1 month and 6 months after SMILE with the lenticule thickness/central corneal thickness (CCT) (R2=0.123,0.145,0.098,all at P<0.05) or between stray light change. Conclusions Intraocular stray light appears less change in operative eyes after SMILE. However, intraocular stray light increases in the eyes received FS-LASIK, especially at early stage after operation. The stray light shifts return to normal with the lapse of postoperative time. Key words: Straylight; Myopia, myopia astigmatism/surgery; Visual quality; Small incision lenticule extraction; Femtosecond laser assisted laser in situ keratomileusis

Comparison of forward light scatter estimations using Shack-Hartmann spot patterns and a straylight meter

To determine whether an unmodified commercial wavefront aberrometer (irx3) can be used to estimate forward light scattering and how this assessment matches estimations obtained from the C-Quant straylight meter. University of Manchester, Manchester, United Kingdom. Prospective comparative study. Measurements obtained with a straylight meter and with Shack-Hartmann spot patterns using a previously reported metric were compared. The method was first validated in a model eye by spraying an aerosol over 4 contact lenses to generate various levels of scattering. Measurements with both methods were subsequently obtained in healthy eyes. The study comprised 33 healthy participants (mean age 38.9 years ± 13.1 [SD]). A good correlation was observed between the density of droplets over the contact lenses and the objective scatter value extracted from the hartmanngrams (r = 0.972, P < .05). However, in eyes of subjects, no significant relationship was found between measurements from the straylight meter and the metric derived from the Shack-Hartmann method (r = 0.133, P = .460). The hartmanngrams provided a valid objective measurement of the light scatter in a model eye; the measurements in human eyes were not significantly correlated with those of the light scatter meter. The straylight meter assesses large-angle scattering, while the Shack-Hartmann method collates information from a narrow angle around the center of the point-spread function; this could be the reason for the difference in measurements. No author has a financial or proprietary interest in any material or method mentioned.

Assessment of Posterior Capsular Opacification of Korean Using Straylight and Glare Sensitivity Meter

Purpose: To evaluate posterior capsular opacity (PCO) using straylight and glare sensitivity meter and to compare availability of straylight and glare sensitivity with known methods for PCO evaluation. Methods: Thirty-six pseudophakic eyes with PCO were selected for this study. Best-corrected visual acuity (BCVA), straylight (C-quant, Oculus GmbH, Wetzlar, Germany) and glare sensitivity (Binoptometer, Oculus GmbH, Wetzlar, Germany) were measured before mydriasis. After mydriasis, PCO images were captured with a slit-lamp and analyzed using the Evaluation of Posterior Capsular Opacification (EPCO) program (EPCO software, University of Heidelberg, Heidelberg, Germany). The same measurements were taken after capsulotomy and compared with pre-capsulotomy data. Results: After capsulotomy, BCVA, EPCO score and straylight were improved with statistical significance (p < 0.05). Cases of PCO with mildly decreased visual acuity showed statistically significantly improved EPCO score and straylight (p < 0.05). Glare sensitivity did not show significant improvement but was statistically significantly correlated with straylight (p = 0.023, Rho = 0.732). Conclusions: Straylight is an available measurement for evaluation of PCO. Glare sensitivity meter which correlates with straylight can be used as a supportive measurement. J Korean Ophthalmol Soc 2015;56(7):998-1005

Repeatability, Reproducibility, and Comparability of Subjective and Objective Measurements of Intraocular Forward Scattering in Healthy Subjects.

Purpose. To assess the repeatability, reproducibility, and comparability of measurements of subjective and objective forward scattering in healthy subjects. Methods. We prospectively examined twenty eyes of 20 healthy volunteers (7 men and 13 women; ages, 28.4 ± 4.1 years). The logarithmic straylight value (log(s)) and the objective scattering index (OSI) were measured with a straylight meter (C-Quant) and a point-spread function meter (OQAS), respectively. Results. The 95% limits of agreement (LoA) between first and second measurements ranged from −0.211 to 0.207 for the C-Quant and from −0.302 to 0.477 for the OQAS. The intraclass correlation coefficients for the repeatability of the log(s) and OSI measurements were 0.815 and 0.926, respectively. The mean difference between examiners was −0.051 ± 0.133 (95% LoA; −0.311 to 0.209) for the C-Quant and 0.080 ± 0.307 (−0.522 to 0.682) for the OQAS. There was a modest, but significant, correlation between the log(s) and the OSI (Spearman correlation coefficient r = 0.498, p = 0.026). Conclusions. The C-Quant and the OQAS provide good repeatability and reproducibility, although the OQAS measurement provides a slightly higher ICC than the C-Quant measurement. The subjective forward scattering may be to some extent expressed in the objective forward scattering in healthy subjects.

Ocular forward light scattering and corneal backward light scattering in patients with dry eye.

To evaluate ocular forward light scattering and corneal backward light scattering in patients with dry eye. Thirty-five eyes in 35 patients with dry eye and 20 eyes of 20 healthy control subjects were enrolled. The 35 dry eyes were classified into two groups according to whether superficial punctate keratopathy in the central 6-mm corneal zone (cSPK) was present or not. Ocular forward light scattering was quantified with a straylight meter. Corneal backward light scattering from the anterior, middle, and posterior corneal parts was assessed with a corneal densitometry program using the Scheimpflug imaging system. Both dry eye groups had significantly higher intraocular forward light scattering than the control group (both P<0.05). The dry eye group with cSPK had significantly higher values in anterior and total corneal backward light scattering than the other two groups. Moderate positive correlations were observed between the cSPK score and corneal backward light scattering from the anterior cornea (R=0.60, P<0.001) and corneal backward light scattering from the total cornea (R=0.54, P<0.001); however, no correlation was found between cSPK score and ocular forward light scattering (R=0.01, P=0.932). Ocular forward light scattering and corneal backward light scattering from the anterior cornea were greater in dry eyes than in normal eyes. Increased corneal backward light scattering in dry eye at least partially results from cSPK overlying the optical zone.

Comparison of optical and psychophysical methods to measure intraocular straylight

AbstractPurpose To quantify intraocular forward scattering (straylight) by using three different methods in a group of normal subjects.Methods Intraocular straylight was measured in the dominant eye of 10 emmetropic subjects without any known ocular pathology (30±5 years).Two different, commercially available, scatter filters (Black Pro‐Mist ¼ and Black Pro‐Mist ½ from Tiffen)where used in order to recreate the effects of higher scattering. Three measurement techniques were used:a commercially available straylight meter (C‐quant, Oculus),a prototype of an optical double‐pass based method (Sigma) and a psychophysical method that we developed.We used a Bayesian method (quick‐CSF) in a range of spatial frequencies (2 to 20 cycles/degree) with 50 2‐alternative forced choice trials.Each set of trials was repeated 2 times for each condition (with and without glare).As a glare source, a fluorescent lamp was positioned concentrically to the test area where the sinusoidal gratings were projected.All tests were presented on a screen placed at 1 meter distance from the subject and the test area was covering a total of 6.4 degrees of visual field.For Sigma and C‐Quant tests,the logarithm of Scatter coefficient was determined, whereas for the q‐CSF measurements the difference between the areas below the log contrast sensitivity curves was used as scatter metrics.Results In the three methods, the effects of straylight were accordingly increasing with the addition of the scatter filters. A correlation between all three methods was verified.Conclusion These results suggest the potential use of an even simplified method based on the q‐CSF to evaluate straylight complementing other existing methods.

Vision-related Quality of Life Before and After Keratoplasty for Fuchs' Endothelial Dystrophy

To assess vision-related quality of life in Fuchs' dystrophy and changes in vision-related quality of life after 3 types of keratoplasty (penetrating keratoplasty [PK], deep lamellar endothelial keratoplasty [DLEK], and Descemet stripping endothelial keratoplasty [DSEK]). Prospective, observational case series. Sixty-three subjects with Fuchs' endothelial dystrophy: 12 subjects (12 eyes) received PK, 11 subjects (11 eyes) received DLEK, and 40 subjects (40 eyes) received DSEK. Subjects were examined before keratoplasty and at regular intervals through 3 years after keratoplasty. At each examination, vision-related quality of life was assessed using the 25-item National Eye Institute Visual Functioning Questionnaire; best spectacle-corrected and uncorrected visual acuities were measured by using the electronic Early Treatment of Diabetic Retinopathy Study protocol; keratometric cylinder was measured by a manual keratometer. Disability glare was measured with a straylight meter. Vision-related quality of life composite score. Vision-related quality of life composite score for all eyes with Fuchs' dystrophy before keratoplasty was 72 ± 11 (n = 63) and did not differ between groups (P = 0.88). Vision-related quality of life improved by 6 months (PK, P = 0.008; DLEK, P = 0.03; DSEK, P < 0.001), with continued improvement between 6 months and 3 years after PK (P = 0.01) and DSEK (P = 0.004). At 6 months, the composite score was higher after DSEK than after PK (P = 0.006). At 3 years, there were no differences in composite scores between the 3 treatments (P = 0.33; mean minimum detectable difference, 8 [α = 0.05; β = 0.20]). After keratoplasty, quality of life was correlated with uncorrected visual acuity at 1 year (r = -0.38; P = 0.001) and at 3 years (r = -0.36; P = 0.02), with disability glare at 3 years (r = -0.41; P = 0.02), and with best-corrected visual acuity at 6 months (r = -0.34; P = 0.03), but not thereafter. Vision-related quality of life in patients with Fuchs' endothelial dystrophy is significantly impaired but improves after keratoplasty, irrespective of the technique. The improvement is faster after DSEK than after PK, and this might be explained in part by rapid improvement in uncorrected visual acuity after DSEK. This study affirms an advantage of endothelial keratoplasty over PK with respect to patient-reported outcomes.

Comparison of methods to quantify posterior capsule opacification using forward and backward light scattering

To compare forward and backward light scattering measurements to quantify posterior capsule opacification (PCO). Vienna Institute for Research in Ocular Surgery, Vienna, Austria. Prospective single-center study. This observational study comprised consecutive patients scheduled for neodymium:YAG (Nd:YAG) capsulotomy for regeneratory PCO. The corrected distance visual acuity (CDVA) using Early Treatment of Diabetic Retinopathy Study charts and the contrast sensitivity under mesopic and photopic conditions using Pelli-Robson charts were assessed before an Nd:YAG capsulotomy was performed. Retroillumination images, rotating Scheimpflug scans (Pentacam HR), and straylight meter (C-Quant) and point-spread function (PSF) meter (Optical Quality Analysis System) measurements were performed before and after Nd:YAG capsulotomy. The study enrolled 50 eyes of 50 patients. The mean uncorrected distance visual acuity and CDVA were 0.76 logMAR ± 0.18 (SD) and 0.68 ± 0.2 logMAR, respectively. The mean log contrast sensitivity (logCS) was 1.2 ± 0.15 logCS under photopic conditions and 1.05 ± 0.15 logCS under mesopic conditions. There was a moderate correlation between the Scheimpflug score and the Automated Quantification of After-Cataract score (r(2) = 0.37, P=.03). Furthermore, a moderate and close to significant correlation between the PSF meter and the straylight meter was observed (r(2) = 0.32; P=.07). Each of the 4 devices assesses different aspects of a patient's quality of vision. Further developments should focus on methods that measure forward scatter of light in a large visual angle and are not too patient or examiner dependent.

Effect of Glistening-Free Intraocular Lens on Intraocular Straylight

Purpose: To compare intraocular straylight between glistening-free and conventional intraocular lenses in pseudophakic eyes. Methods: Straylight values were measured prospectively in 21 eyes with glistening-free pseudophakic lenses (group A, model enVistaTM, Bausch & Lomb, Inc., USA) and 79 eyes with conventional hydrophilic pseudophakic lenses (group B, model Akreos MI-60, Bausch & Lomb, Inc., USA). Best corrected visual acuity (BCVA) and straylight were measured preoperatively and 1 month and 2 months postoperatively using C-quant straylight meter (Oculus GmbH, Wetzlar, Germany). Results: There were no statistically significant differences of BCVA preoperatively or 2 months postoperatively between the 2 groups (p > 0.05). BCVA and straylight significantly improved after the operation (p 0.05). Conclusions: In terms of straylight, glistening-free intraocular lenses were not beneficial. Although straylight was not statistically significant, other correlations between glistening and visual function should be investigated. J Korean Ophthalmol Soc 2014;55(7):1001-1006

Long-term changes in straylight induced by corneal refractive therapy: A pilot study

To assess long-term intraocular straylight changes induced by corneal refractive therapy (CRT) and to determine whether these changes persist after cessation of CRT lens wear. A single-center, prospective, longitudinal study was performed in 22 subjects (group 1) undergoing overnight corneal refractive therapy for 1 year. Ten right eyes of 10 subjects (group 2) with emmetropia served as controls. In each subject, high contrast visual acuity (HCVA), manifest refraction and intraocular straylight were determined at several time points during treatment and 1 month after discontinuing treatment. Straylight was measured using the van den Berg straylight meter (third generation). EDTRS charts (logMAR units) were used to assess HCVA. For both groups, only data for the right eyes were analyzed. Straylight (mean ± standard deviation) significantly fell from baseline (0.98 ± 0.13) to values recorded after 1 month (0.88 ± 0.13, p=0.011), 3 months (0.88 ± 0.13, p=0.004), 6 months (0.88 ± 0.13, p=0.000) and 12 months (0.76 ± 0.12, p=0.003) of treatment. One month after discontinuing CRT lens wear, straylight was still significantly lower than baseline (0.89 ± 0.13, p=0.003). No correlations were observed between intraocular straylight and HCVA. Good refractive outcomes and reductions in straylight were observed in response to corneal refractive therapy for myopia. The reduction in straylight observed after discontinuing CRT warrents further investigation.

Objectivity and reliability of the C‐Quant in a clinical setting

AbstractThe fact that the (C‐quant) Straylight Meter measures the straylight as the subject actually sees it (and is disturbed by it) may be considered as a limitation of the technique, when used in a clinical environment. Because it is a psychophysical technique, reliability of individual measurements needs to be checked (as with visual field measurents). We decided to evaluate the objectivity and reliability in patients with cataract in a regular clinical environment. For this very purpose, we studied the reliability parameter (ESD), designed to predict the accuracy of an individual measurement. We also tried to simulate frauds.

Intraocular Straylight After Thin-Flap LASIK With a Femtosecond Laser Versus a Mechanical Microkeratome

To investigate characteristics of straylight before and after thin-flap LASIK performed with femtosecond laser versus with mechanical microkeratome and assess changes at 1 day, 1 week, 1 month, 6 months, and 1 year postoperatively. One hundred twenty-eight consecutive eyes from 66 patients were included in this prospective study. Sixty-one eyes of 31 patients had thin-flap LASIK with femtosecond laser. In addition, 67 eyes from 35 patients underwent thin-flap LASIK with mechanical microkeratome were included for comparison. Following flap creation, all eyes were ablated using the VIXS S4 excimer laser system (Visx USA, Inc., Santa Clara, CA). Straylight values were measured using the C-Quant straylight meter (Oculus Optikgeräte GmbH, Wetzlar, Germany) preoperatively and 1 day, 1 week, 1 month, 6 months and 1 year postoperatively. Preoperatively, the mean straylight values were 0.93 ± 0.11. After femtosecond laser-assisted thin-flap LASIK, the values were 1.00 ± 0.11, 0.98 ± 0.10, and 0.99 ± 0.12 at 1 day, 1 week, and 1 month, respectively, and significantly increased (F = 7.62, P > .0001) compared to preoperative values. However, these values decreased and returned to preoperative levels at 6 months and 1 year postoperatively (0.92 ± 0.09 and 0.89 ± 0.13, respectively; P > .05). The postoperative-preoperative increases in straylight were reduced in the femtosecond laser group compared to the mechanical microkeratome group (0.05 ± 0.13 vs 0.10 ± 0.13 at 1 month postoperatively; P < .05). This difference was statistically significant at 1 month postoperatively (P = .04). A negative significant correlation was also found between preoperative straylight values and postoperative-preoperative increases. Straylight increased significantly in the early stages after femtosecond laser-assisted thin-flap LASIK. However, these values improved over time and gradually returned to preoperative levels, which may be related to the progression of corneal healing.

Straylight measurements as an indication for cataract surgery

To assess adding straylight measurements to the indication for cataract surgery. Onze Lieve Vrouwe Hospital, Amsterdam, and Zonnestraal Eye Clinic, Hilversum, The Netherlands. Prospective interventional cohort study. Before and after cataract extraction, corrected distance visual acuity (CDVA) and straylight were recorded in all patients. Subjective complaints were documented by the 39-item National Eye Institute Visual Function Questionnaire (NEI VFQ-39) and a straylight questionnaire. The population comprised 217 patients with a mean age of 72 years ± 9.12 (SD) (range 29 to 90 years). Preoperatively, the mean straylight was 1.55 ± 0.29 log(s) and the mean CDVA, 0.28 ± 0.21 logMAR. Visual acuity and straylight showed little correlation (R(2) = 0.08). The mean postoperative improvement in CDVA was 0.26 ± 0.20 logMAR (range -0.12 to 1.12 logMAR) and in straylight, 0.31 ± 0.32 log(s) (range -0.50 to 1.27 log[s]). The preoperative breakeven point (50% chance of postoperative improvement) was 0.06 logMAR for CDVA and 1.29 log(s) for straylight. Preoperative and postoperative questionnaires showed straylight had almost the same influence as visual acuity on quality of vision. Straylight and visual acuity measure different aspects of quality of vision and influenced subjective visual quality almost equally. When straylight was added to preoperative considerations of cataract extraction, postoperative results were more predictable. The Netherlands Academy of Arts and Sciences has a proprietary interest in the C-Quant Straylight meter. No author has a financial or proprietary interest in any material or method mentioned.

Comparative Resilience of Clinical Perimetric Tests to Induced Levels of Intraocular Straylight

PURPOSE To investigate the effect of intraocular straylight (IOS) induced by white opacity filters (WOF) on threshold measurements for stimuli employed in three perimeters: standard automated perimetry (SAP), pulsar perimetry (PP) and the Moorfields motion displacement test (MDT). METHODS Four healthy young (24-28 years old) observers were tested six times with each perimeter, each time with one of five different WOFs and once without, inducing various levels of IOS (from 10% to 200%). An increase in IOS was measured with a straylight meter. The change in sensitivity from baseline was normalized, allowing comparison of standardized (z) scores (change divided by the SD of normative values) for each instrument. RESULTS SAP and PP thresholds were significantly affected (P < 0.001) by moderate to large increases in IOS (50%-200%). The drop in motion displacement (MD) from baseline with WOF 5, was approximately 5 dB, in both SAP and PP which represents a clinically significant loss; in contrast the change in MD with MDT was on average 1 minute of arc, which is not likely to indicate a clinically significant loss. CONCLUSIONS The Moorfields MDT is more robust to the effects of additional straylight in comparison with SAP or PP.

Comparative Resilience of Clinical Perimetric Tests to Induced Levels of Intraocular Straylight

To investigate the effect of intraocular straylight (IOS) induced by white opacity filters (WOF) on threshold measurements for stimuli employed in three perimeters: standard automated perimetry (SAP), pulsar perimetry (PP) and the Moorfields motion displacement test (MDT). Four healthy young (24-28 years old) observers were tested six times with each perimeter, each time with one of five different WOFs and once without, inducing various levels of IOS (from 10% to 200%). An increase in IOS was measured with a straylight meter. The change in sensitivity from baseline was normalized, allowing comparison of standardized (z) scores (change divided by the SD of normative values) for each instrument. SAP and PP thresholds were significantly affected (P < 0.001) by moderate to large increases in IOS (50%-200%). The drop in motion displacement (MD) from baseline with WOF 5, was approximately 5 dB, in both SAP and PP which represents a clinically significant loss; in contrast the change in MD with MDT was on average 1 minute of arc, which is not likely to indicate a clinically significant loss. The Moorfields MDT is more robust to the effects of additional straylight in comparison with SAP or PP.

Repeatability and reproducibility of retinal straylight measurement using C-Quant compensation comparison method

Background In an ideal eye there would be no light scattering at all,but the eye media is not optically ideal.Intraocular straylight causes a veil of light and reduction in the contrast of the retinal image and thus decrease the quality of vision. Objective The present study was to investigate the repeatability and reproducibility of C-Quant straylight meter( Oculus,Germany) in measuring retinal straylight of myopia and post-laser in situ keratomileusis(LASIK) corneas. Methods This is a prospective research.The consecutive 35 eyes of 21 myopic patients and 34 eyes of 22 patients who received LASIK were included in this trail.Retinal straylight was measured for 7 times at a period of time and analyzed quantificational to evaluate the repeatability of measurement.Thirty-eight eyes of 19 patients were measured again at 3-7 days for 3 times at a period of time to assess the reproducibility of C-Quant straylight meter.The mean standard difference (SD) and coefficient of variation (CV) were used as the credibility evaluation.This clinical study complied with Helsinki Declaration and the informed consent was obtained prior to the medical procedure. Results The straylight Log(s) of 7 times measurement were all less than 0.95.The mean Log(s) were 0.92±0.12 and 0.93±0.17 respectively in myopia group and post-LASIK group,without statistically significant differences among 7 times measurement( F=0.335,P=0.812;F=1.000,P=0.409).The mean SD for the 7 times measurement was 0.07 Log units.SD and CV increased with the number of measurements.The differences of mean SD and CV between 3 times result and 6 times result were significant different (t =-2.080,P =0.045;t =-2.190,P =0.035 ).No difference was found between different time periods( t =-0.531,P=0.598 ).The difference of the results between two measurements from the same patient was 0.013. ConclusionsC-Quant is a noncontact,noninvade,rapid and convenient method for the measurement of straylight in myopia and post-LASIK eyes due to the high repeatability and reproducibility. Key words: C-Quant; Straylight; Myopia; Laser in situ keratomileusis; Repeatability; Reproducibility

Straylight and Contrast Sensitivity After Corneal Refractive Therapy

To compare intraocular straylight and contrast sensitivity determined before corneal refractive therapy and after 15 days and 1 month of treatment. A single-center, prospective, and longitudinal study was performed in 30 subjects undergoing corneal refractive therapy. In each subject, high-contrast visual acuity (HCVA), low-contrast visual acuity (LCVA), straylight, and contrast sensitivity were determined at baseline and after 15 days and 1 month after the treatment. Straylight was measured using the van den Berg straylight meter (third generation). Contrast sensitivity was determined under both photopic and mesopic conditions using the VCTS 6500 instrument (Vision Contrast Test System). EDTRS charts (logMAR units) were used to measure HCVA and LCVA. Straylight (mean ± standard deviation) significantly fell from baseline (0.94 ± 0.14) to the values recorded at 1 month (0.85 ± 0.11, p = 0.009). Photopic contrast sensitivity remained stable yet mesopic contrast sensitivity measured at high spatial frequencies was significantly reduced. No correlations between intraocular straylight and contrast sensitivity, HCVA, or LCVA were observed 15 days and 1 month after corneal refractive therapy. Our findings suggest improved intraocular straylight readings 1 month after starting the treatment, although the changes observed in straylight could not be related to changes in mesopic and photopic contrast sensitivity or HCVA and LCVA. Mesopic contrast sensitivity was more affected by the treatment intervention than photopic contrast sensitivity.

Variation of straylight between contra lateral eyes - results from 1017 healthy subjects

Editor, A large multicentre study on the vision of European drivers (GLARE study) was carried out in five participating clinics in Amsterdam, Salzburg, Tübingen, Barcelona and Antwerp, where 2422 volunteers underwent a series of visual function tests, including tests for visual acuity (VA), visual field (VF), contrast sensitivity, straylight and useful field of view (UFOV). Special attention was paid to intraocular straylight increase because of ageing of the crystalline lens (Van den Berg et al. 2007; Michael et al. 2009; Van Rijn et al. 2009; Nischler et al. 2010). The intraocular straylight parameter (log [s]) was obtained using the compensation comparison technique, as employed in the C-Quant (Oculus GmbH, Wetzlar, Germany) straylight meter. For each eye, two consecutive measurements were taken, starting with the right eye. This technique has proved to give reliable and objective measurements of intraocular straylight (Coppens et al. 2006; Van den Berg et al. 2009). We analysed the straylight values of 1017 healthy phakic individuals from the GLARE study, who were without any ocular pathology such as glaucoma, diabetic retinopathy, macular degeneration, dry eye, amblyopia and cataract (LOCS III >1.5), to further confirm the repeatability of the test and to assess the difference in straylight between contra lateral eyes. We found no statistically significant or clinically relevant difference between straylight repeated measures. The differences between repeated log(s) values had a mean and standard deviation for the right eyes of 0.0042 ± 0.0992 and 0.0034 ± 0.1043 for the left eyes, corresponding to repeated measures standard deviations of 0.0702 and 0.0738, respectively. This yields an average standard deviation for repeated measures of 0.0720 (root mean square of 0.0702 and 0.0738), which remains stable with different levels of straylight (see Fig. 1A). The repeatability obtained is in agreement with the results reported by Coppens et al. (2006), Cerviño et al. (2008), and others. The mean differences are virtually zero and statistically not significant, indicating that no learning effect exists. (A) Scatter plot of repeated measures. Straylight variation between first and second measurement remains stable at all straylight values. –––, x = y. (B) Difference in straylight values between right and left eyes seems to have a tendency to increase with higher values of straylight. –––, mean difference; - - -, 95% confidence interval. (C) Difference in straylight values between right and left eyes as function of age shows a slight tendency to increase with age, until the age of 75, where it seems to drop back. –––, mean difference; - - -, 95% confidence interval. For the straylight differences between right and left eyes, we found a mean and standard deviation of −0.0047 ± 0.1158 log(s), respectively (Fig. 1B). The standard deviation is higher as would be expected from the repeated measures differences reported earlier (0.0720), as the differences between both eyes were based upon averages of two values for each individual eye. According to anova analysis, the statistical significance of this effect is p < 0.0001. Furthermore, the standard deviation of the intra-eye difference progressively increased with age (Fig. 1C), probably due to the asymmetrical evolution of lens ageing, going from 0.0985 around 35 years, 0.1114 from 45 to 60 years, and 0.1277 from 61 years upward. Those differences are statistically significant (p = 0.023). For the group above 75 years of age, the standard deviation of the difference seems to drop back a little (to 0.1154); nonetheless, this difference is not statistically significant (F test, p = 0.16). The mean difference is virtually zero and statistically not significant (paired t-test, p = 0.172), confirming that no learning effect exists. Although the differences between contra lateral eyes are not very large, it is interesting to speculate about the cause. It can be considered that contra lateral eyes from a same person have slightly different straylight levels, just as any other part of the body is slightly asymmetrical to their contra lateral counterpart. It requires a focused study, especially interesting in the <45-year group, what may cause these differences. The standard deviation of the straylight difference between eyes gives us a good base to estimate the acceptable difference in straylight after a procedure in one eye using the value of the contra lateral healthy eye as control.

Forward light scatter and contrast sensitivity in keratoconic patients

The aim of this study was to obtain intraocular forward light scatter (FLS) data in keratoconus patients and to explore possible relationships with contrast sensitivity. Intraocular straylight was assessed in the right eye of 10 visually-normal subjects (31±5 years) and 5 keratoconus patients (34±9 years) using the van den Berg straylight meter. Contrast sensitivity was also measured in both groups, with and without a glare source provided by the Brightness Acuity Tester (BAT), using a Pelli-Robson chart. Inclusion criteria for the keratoconic patients were chosen to avoid natural causes of increased scatter and to limit the influence of factors that could affect the straylight measurements. Intraocular light scatter was significantly greater in the keratoconic patients than in normal subjects for each of the three eccentricities tested (Mann-Whitney U test (2-tailed): Z≤-2.2, p≤0.027). Baseline Pelli-Robson contrast sensitivity was also found to be lower in the keratoconus group than in the normal subjects (Mann-Whitney U test: Z=-2.2, p=0.023). Under glare conditions contrast loss was significantly greater in the keratoconic patients than in the normal subjects (Mann-Whitney U test: Z=-2.5, p=0.013). High levels of negative correlation were found between the magnitudes of intraocular straylight and baseline contrast sensitivity in the keratoconus group (Spearman's correlation coefficient (RS)≤-0.87, p≤0.027). The high values of straylight measured in the keratoconic patients cannot be explained by age or scarring and could be related to the structural degradation of the cornea. Further investigation of intraocular scatter in keratoconus is warranted to improve our current understanding of the visual deficits associated with this pathology.

The Effect of Induced Intraocular Straylight on Perimetric Tests

To investigate the effect of intraocular straylight (IOS) on threshold measurements made by four types of perimetry: standard automated perimetry (SAP), frequency-doubling technology (FDT) perimetry, flicker-defined form (FDF) perimetry, and the Moorfields Motion Displacement Test (MDT). Six healthy young (21-29 years) psychophysically experienced observers were tested five times with each perimeter, each time with one of five different white opacity filters (WOFs), to induce various levels of IOS. Each WOF gave rise to an increase in IOS, measured with a straylight meter, of between 10% and 200% from baseline and ranging in effect from normal ageing to significant cataract. The change in sensitivity from baseline was normalized, allowing comparison of standardized (z) scores (change divided by the standard deviation of normative values) for each instrument. Average SAP, FDT, and FDF thresholds were significantly affected (P < 0.001) by moderate to large increases in IOS (50%-200%), whereas MDT remained largely unaffected over the same range of straylight levels. The Moorfields MDT shows greater resilience to the effects of additional straylight compared with SAP, FDT, or FDF.