Alan Cayless

Interactive screen experiments: innovative virtual laboratories for distance learners

The desirability and value of laboratory work for physics students is a well-established principle and issues arise where students are inherently remote from their host institution, as is the case for the UKs Open University. In this paper, we present developments from the Physics Innovations Centre for Excellence in Teaching and Learning (piCETL) in the production and technology of the virtual laboratory resources, interactive screen experiments, and the benefits and drawbacks of such resources. We also explore the motivations behind current implementation of interactive screen experiments and examine evaluation strategies and outcomes through a series of case studies.

Comparison of 3 biometry devices in cataract patients.

Purpose Accurate biometry is an obligatory preoperative measurement for refractive surgery as well as cataract surgery. A new device based on partial coherence interferometry was compared with 2 currently used biometry devices. Setting Department of Ophthalmology, Saarland University Medical Center, Homburg, Germany. Design Prospective case series. Methods Eyes of cataract patients were examined with a functional prototype of the new optical low‐coherence reflectometry (OLCR) biometer OA‐2000, the standard OLCR biometer Lenstar, and the partial coherence interferometry (PCI) biometer IOLMaster. The results were compared using a Wilcoxon‐Mann‐Whitney U test and Pearson correlation calculations. Results A total of 138 eyes of 74 cataract patients were examined. Pearson correlation showed excellent correlation for axial length, anterior chamber depth and keratometry among the 3 devices tested. The highest correlation was found between standard OLCR biometer and PCI biometer for AL, R1, and R2 (r = 1.0, r = 0.936, r = 0.952, respectively; all P ≤ .001). For anterior chamber depth (ACD), the highest correlation was found between the standard OLCR biometer and the new OLCR biometer (r = 0.943; P ≤ .001). The mean values of AL/ACD/R1/R2 differed very little, but the differences were significant (all P ≤ .05) (new OLCR biometer 23.31/3.21/7.74/7.64 mm; standard OLCR biometer 23.30/3.13/7.80/7.60 mm; PCI biometer 23.37/3.00/7.78/7.6 mm). Conclusions Compared with other clinical instruments, the new OLCR biometer generated the most accurate results. Differences especially in measurement of axial length were statistically but not clinically significant. The new OLCR biometer yielded results that correlated very well with the values of the PCI biometer and standard OLCR biometer. Financial Disclosure None of the authors has a financial or proprietary interest in any material or method mentioned.

Staging of keratoconus indices regarding tomography, topography, and biomechanical measurements.

PURPOSE To derive limits of metric keratoconus indices for classification into keratoconus stages. DESIGN Validity and reliability analysis of diagnostic tools. METHODS A total of 126 patients from the keratoconus center of Homburg/Saar were evaluated with respect to Amsler criteria, using Pentacam (Keratoconus Index [KI], Topographic Keratoconus Classification [TKC]), Topographic Modeling System (Smolek/Klyce, Klyce/Maeda), and Ocular Response Analyzer (Keratoconus Match Probability [KMP], Keratoconus Match Index [KMI]). Mean value, standard deviation, 90% confidence interval, and the Youden J index for definition of the thresholds were evaluated. RESULTS For separation of keratoconus stages 0/1/2/3/4 we derived the following optimum thresholds: for KI 1.05/1.15/1.31/1.49 and for KMI 0.77/0.32/-0.08/-0.3. For Smolek/Klyce and Klyce/Maeda high standard deviations and overlapping confidence intervals were found; therefore no discrete thresholds could be defined. Nevertheless, for them we still found a good sensitivity and specificity in discriminating between healthy (stage 0) and keratoconus (stages 2-4) eyes in comparison with the other indices. CONCLUSIONS We derived thresholds for the metric keratoconus indices KI and KMI, which allow classification of keratoconus stages. These now need to be validated in clinical use. Smolek/Klyce and Klyce/Maeda were not sufficiently sensitive to allow classification into individual stages, but these indices did show a good specificity and sensitivity in discriminating between keratoconus and healthy eyes.

First results of automated RAPD-SWIFT method in dynamic pupillometry

BACKGROUND This paper presents preliminary observations on the use of a commercial pupillometric instrument (Albomed PupilX) for the detection and quantification of Relative Afferent Pupillary Defect (RAPD). In this pilot study, video-based pupillometry was used in conjunction with calibrated LED illumination to simulate the effects of the traditional swinging-flashlight test using neutral density filters. METHODS The results presented in this study follow a method described by Wilhelm et al. (Tübingen SWIFT-test) in which the eyes are illuminated alternately and the response in pupil diameter measured by video pupillometry. Using the PupilX instrument, the LED intensity can be programmed in logarithmic steps starting from a maximum intensity of 1000 lux (lx), with each reduction of 50% in illumination intensity corresponding to a 0.3 log-units increase in filter density. RESULTS The eyes were stimulated unilaterally with illumination intensities corresponding to a neutral density range of 0.0 to 0.9 log-units. In all normal subjects a symmetrical pupil reaction was seen, independent of which eye was stimulated. In contrast, in a subject with known RAPD, a clear asymmetry in the reaction to stimulation of the left and the right eyes was seen. CONCLUSIONS These measurements were compared with typical results from the original Tübingen SWIFT study and good qualitative agreement was seen. Furthermore, the method can clearly differentiate between healthy subjects and those with a known RAPD, indicating that the PupilX, programmed with specific stimulus sequences and in conjunction with a suitable analysis software, has the potential for recognition and quantification of RAPD, and prompting the suggestion for further study involving a range of patients including both normal subjects and those with a known and quantified RAPD.

Ghost-image analysis in phakic intraocular lenses with central hole as a potential cause of dysphotopsia.

Purpose To analyse the optical effect of an artificial hole in the optic centre of posterior chamber phakic intraocular lenses. Setting Institute of Experimental Ophthalmology, Saarland University, Homburg/Saar, Germany. Design Experimental simulation study. Methods Four eye models with an ametropia of −4 D, −8 D, +4 D, and +8 D were created in the ray tracing software ASAP. Refractive correction of these models was implemented with a model of an Implantable Collamer Lens (ICL). Each eye was set up twice with 1 eye receiving a conventional ICL without a central hole and the second an ICL with a central hole. Ray bundles were traced for lateral visual field angles from 0 to 60 degrees in steps of 1 degree. Ray propagation and retinal illumination were then compared between the 2 ICL models. Results All eye models showed ghost images originating from the anterior surface of the ICL. Eye models with the ICL with central hole showed additional light spots in the peripheral areas of the retina originating from reflections at the cylindrical wall of the central hole in the ICL. The average intensity of ghost images in the temporal retinal hemisphere was between 30 and 40 dB less than the maximum intensity of the primary image. Conclusion A central hole within a posterior chamber phakic intraocular lens may cause stray light and ghost images (positive dysphotopsia) although the on‐axis visual quality of the eye with the ICL is mostly unaffected. Financial Disclosure The authors have no financial interest in any of the material presented in this paper.

Reproducibility and normal values of static pupil diameters

Purpose: To provide additional information on normal values of static pupil diameter measurements for binocular infrared pupillometry with PupilX, a commercial pupillometer, and assess the reproducibility of this device’s measurements. Methods: The pupil diameters from 91 study participants with normal eyes with an average age of 39.7 years (SD 16.4 years) were measured with PupilX under scotopic (0 lx), mesopic (1 lx), and photopic (16 lx) illumination. To assess the repeatability of the device, each measurement was repeated 5 times. Results: The mean pupil diameters were 6.5 mm (SD 1.3 mm), 5.5 mm (SD 1.2 mm), and 4.03 mm (SD 0.9 mm) under scotopic, mesopic, and photopic illumination. Left and right eyes showed no difference in mean pupil diameters. The mean unsigned anisocoria was 0.26 mm (SD 0.32 mm) under scotopic, 0.26 mm (SD 0.27 mm) under mesopic, and 0.19 mm (SD 0.19 mm) under photopic illumination. The decrease in pupil diameter with age was largest for scotopic (≈0.057 mm/y) and smallest for photopic illumination (≈0.025 mm/y). The repeatability of the pupillometer was better than 0.2 mm. Conclusions: This study provides reference values for age- and light-related pupil diameters measured with the PupilX digital pupillometer in normal subjects.

Endothelial alterations in 712 keratoconus patients

To investigate the effect of the severity of keratoconus on the corneal endothelium using specular microscopy.

Aberration-free intraocular lenses – What does this really mean?

BACKGROUND So-called aberration-free intraocular lenses (IOLs) are well established in modern cataract surgery. Usually, they are designed to perfectly refract a collimated light beam onto the focal point. METHODS We show how much aberration can be expected with such an IOL in a convergent light beam such as that found anterior to the human cornea. Additionally, the aberration in a collimated beam is estimated for an IOL that has no aberrations in the convergent beam. The convergent beam is modelled as the pencil of rays corresponding to the spherical wavefront resulting from a typical corneal power of 43m-1. The IOLs are modelled as infinitely thin phase plates with 20m-1 optical power placed 5mm behind the cornea. Their aberrations are reported in terms of optical path length difference and longitudinal spherical aberration (LSA) of the marginal rays, as well as nominal spherical aberration (SA) calculated based on a Zernike representation of the wavefront-error at the corneal plane within a 6mm aperture. RESULTS The IOL designed to have no aberrations in a collimated light beam has an optical path length difference of -1.8μm, and LSA of 0.15m-1 in the convergent beam of a typical eye. The corresponding nominal SA is 0.065μm. The IOL designed to have no aberrations in a convergent light beam has an optical path length difference of 1.8μm, and LSA of -0.15m-1 in the collimated beam. CONCLUSIONS An IOL designed to have no aberrations in a collimated light beam will increase the SA of a patients eye after implantation.

Complementary Keratoconus Indices Based on Topographical Interpretation of Biomechanical Waveform Parameters: A Supplement to Established Keratoconus Indices

Purpose. To build new models with the Ocular Response Analyzer (ORA) waveform parameters to create new indices analogous to established topographic keratoconus indices. Method. Biomechanical, tomographic, and topographic measurements of 505 eyes from the Homburger Keratoconus Centre were included. Thirty-seven waveform parameters (WF) were derived from the biomechanical measurement with the ORA. Area under curve (ROC, receiver operating characteristic) was used to quantify the screening performance. A logistic regression analysis was used to create two new keratoconus prediction models based on these waveform parameters to resample the clinically established keratoconus indices from Pentacam and TMS-5. Results. ROC curves show the best results for the waveform parameters p1area, p2area, h1, h2, dive1, mslew1, aspect1, aplhf, and dslope1. The new keratoconus prediction model to resample the Pentacam topographic keratoconus index (TKC) was WFTKC = −4.068 + 0.002 × p2area − 0.005 × dive1 − 0.01 × h1 − 2.501 × aplhf, which achieves a sensitivity of 90.3% and specificity of 89.4%; to resample the TMS-5 keratoconus classification index (KCI) it was WFKCI = −3.606 + 0.002 × p2area, which achieves a sensitivity of 75.4% and a specificity of 81.8%. Conclusion. In addition to the biomechanically provided Keratoconus Index two new indices which were based on the topographic gold standards (either Pentacam or TMS-5) were created. Of course, these do not replace the original topographic measurement.