S. Goebels

Precision of Ocular Response Analyzer

Purpose: To evaluate the repeatability of corneal hysteresis (CH) and corneal resistance measurements as well as the consistency of the four shots within each measurement using the ocular response analyzer (ORA, Reichert Ophthalmic Instruments, Depew, NY) and to generate a pool of data of a normal population. Methods: A total of 45 eyes from 45 healthy volunteers without ocular pathologies and normal visual acuity were enrolled in this study. A sequence of five consecutive measurements was performed with each patient with the ORA. The biomechanical properties of the cornea in terms of CH and corneal resistance factor (CRF) were recorded, as well as the Goldmann-correlated IOP (IOPg) and cornea correlated IOP (IOPcc). The trend in each measurement sequence was analyzed and Cronbach’s α was derived for the repeatability. The average of four shots within each measurement was compared with the best signal value (BSV) provided by the internal data processing of the ORA. Results: Mean value for CH was 11.58 and BSV was 11.55. For CRF, mean value was 11.21 and BSV was 11.28. No significant difference was found between the average value and the BSV of one measurement (p > 0.05). No significant difference was found between the average value and the BSV of the five consecutive measurements, only IOPg showed a significant difference (p = 0.017), average value of IOPg is higher than BSV. Within a sequence of five measurements for each individual, the average values of the four shots per measurement for IOPg and IOPcc are decreasing by 1.19 and 1.05 mmHg on average. The repeatability test revealed good results for CH and CRF (all α are higher than 0.9). Conclusion: The ORA provides, beside intraocular pressure additional, information about the biomechanical properties of the cornea such as hysteresis and resistance. It proves to yield good repeatability for corneal hysteresis and resistance in normal subjects.

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.

Vignetting and field of view with the KAMRA corneal inlay.

Purpose. To evaluate the effect of the KAMRA corneal inlay on the retinal image brightness in the peripheral visual field. Methods. A KAMRA inlay was “implanted” into a theoretical eye model in a corneal depth of 200 microns. Corneal radius was varied to a steep, normal, and flat (7.37, 7.77, and 8.17 mm) version keeping the proportion of anterior to posterior radius constant. Pupil size was varied from 2.0 to 5.0 mm. Image brightness was determined for field angles from −70° to 70° with and without KAMRA and proportion of light attenuation was recorded. Results. In our parameter space, the attenuation in brightness ranges in between 0 and 60%. The attenuation in brightness is not affected by corneal shape. For large field angles where the incident ray bundle is passing through the peripheral cornea, brightness is not affected. For combinations of small pupil sizes (2.0 and 2.5 mm) and field angles of 20–40°, up to 60% of light may be blocked with the KAMRA. Conclusion. For combinations of pupil sizes and field angles, the attenuation of image brightness reaches levels up to 60%. Our theoretical findings have to be clinically validated with detailed investigation of this vignetting effect.

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.

Comparison of the New Biometer OA-1000 with IOLMaster and Tomey AL-3000

Abstract Background: The OA-1000 (Tomey, Japan) is a new optical biometer, which allows measurements of axial length (AL), anterior chamber depth (ACD) and corneal thickness (CT) due to partial coherence interferometry (PCI) technology. The aim of this study was to compare the OA-1000 results with those obtained with the IOLMaster and contact applanation A-scan ultrasonography. Methods: We examined 133 eyes of 75 patients with age related cataract. Mean age was 72.0 ± 9.5 years. Biometry measurements of AL and ACD were performed with the Tomey OA-1000 based on PCI, the IOLMaster based on PCI (AL) and slit projection (ACD), and the Tomey AL-3000 based on contact applanation A-scan ultrasonography. Results: Mean AL using the IOLMaster was 23.21 ± 1.08 mm, using the AL-3000 was 22.79 ± 1.04 mm, using the OA-1000 it was 22.97 ± 1.1 mm. Mean ACD using the IOLMaster was 2.99 ± 0.41 mm, using the OA-1000 3.40 ± 0.46 mm, using the Tomey AL-3000 it was 2.93 ± 0.43 mm. Mean difference between the AL and ACD measured with the OA-1000 and the IOLMaster was 0.22 ± 0.047 mm and 0.40 ± 0.33 mm, between OA-1000 and the AL-3000 it was 0.19 ± 0.23 mm and 0.47 ± 0.33 mm, and between IOLMaster and AL-3000 it was 0.42 ± 0.23 and 0.09 ± 0.36 mm. For AL the correlation coefficient R between IOLMaster and OA-1000 was 0.999, between IOLMaster and AL-3000 it was 0.976, between AL-3000 and OA-1000 it was 0.977. For ACD R between IOLMaster and OA-1000 was 0.735, between IOLMaster and AL-3000 it was 0.822, between AL-3000 and OA-1000 it was 0.716 (all p < 0.001). Conclusions: Compared with other used clinical instruments the OA-1000 generates accurate results. Although differences were found, the OA-1000 provided results that correlated well with the values of IOLMaster and AL-3000.

Reproducibility of the Optical Biometer OA-1000 (Tomey)

Aim. The OA-1000 (Tomey, Japan) is a new optical biometer, which measures axial length (AL), anterior chamber depth (ACD), and central corneal thickness (CT) utilizing optical interference technology. The aim of this study was to prove the reproducibility which is considered fundamental for other clinical investigations. Methods. 55 healthy volunteers were enrolled in this study. For each measurement of AL, ACD, and CT the biometer is grabbing a sequence of 10 shots and mean value (mean) and standard deviation (SD) are displayed. Five consecutive measurements were performed and average and standard deviation were assessed. Cronbachs α was derived as a quality measure for reproducibility. Results. For AL measurement Cronbachs α was 1.000, for CT 0.999, and for ACD 0.979, respectively. Mean value for AL was 23.36 ± 1.03 mm, for ACD it was 3.60 ± 0.687 mm, and for CT it was 552.08 ± 29.70 μm, respectively. Standard deviation for AL was 0.013 ± 0.022 mm, for ACD 0.09 ± 0.11 mm, and for CT 2.18 ± 1.75 μm. One correlation was found between mean values for AL and ACD (R = 0.388, P = 0.005); no other correlations were found between mean values or values of standard deviation of AL, ACD, or CT. Conclusion. The OA-1000 shows an excellent reproducibility for measurement of AL, ACD, and CT and can be used in clinical practice.

Can retinoscopy keep up in keratoconus diagnosis

PURPOSE To evaluate the diagnostic potential of retinoscopy in comparison with Amsler-grading, Pentacam and Ocular Response Analyzer (ORA) in classifying keratoconus stages. METHODS Clinical examination, retinoscopy, Pentacam and ORA were performed in 126 patients. Data of Amsler, retinoscopy, topographic keratoconus classification (TKC) of Pentacam and keratoconus match probability (KMP) of ORA were analyzed. Each of these four classification techniques quotes keratoconus into stage 0 (normal) to 4 (severe). Descriptive analysis and cross tables were used to compare the different devices. RESULTS For retinoscopy the distribution in the five keratoconus grades normal/suspect/mild/moderate/severe (in numbers) was 34/33/34/17/8. For Amsler it was 37/36/35/12/4, for TKC 38/17/34/31/4, for KMP 32/34/32/15/9. The cross tables show large classification differences of all devices. Overall, classification of retinoscopy and Amsler/TKC/KMP is congruent in 51.6%/36.3%/39.8% of the cases. Of all eyes, Amsler was congruent with TKC/KMP in 54.0%/48.4%, and TKC and KMP were congruent in 53.3%. In a binary decision (normal vs. any stage of mild/moderate/severe) matching between retinoscopy and Amsler/TKC/KMP was 98.6%/88.8%/82.4%. Sensitivity/specificity for retinoscopy and Amsler, TKC, KMP was 98.8%/94.0%, 84.4%/100% and 80.0%/79.1%. CONCLUSIONS The congruence of keratoconus classification was very poor of all the techniques tested in our study. This applies to objective measures such as TKC, KMP as well as clinical classification techniques such as Amsler and retinoscopy. Compared to TKC and KMP, retinoscopy underestimates keratoconus stages. In contrast, the performance of binary decisions (normal vs. keratoconus) shows a high sensitivity and specificity. Retinoscopy, however, showed a clear clinical use in confirming the diagnosis of keratoconus.

Endothelial alterations in 712 keratoconus patients

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

[Keratoconus lenses: the small correction miracle].

Keratoconus is a non-inflammatory corneal disease associated with a cone-shaped protrusion and progressive corneal thinning. Apart from progression control and stabilizing interventions, correcting the optical error induced by a mostly highly irregular corneal surface is of paramount importance with respect to quality of life and ability to work. This goal can be achieved efficiently by contact lenses with only rare adverse conditions. This article provides a current overview on contact lens fitting in keratoconus and presents own associated results.ZusammenfassungDer Keratokonus ist eine nichtentzündliche Hornhauterkrankung, die mit einer kegelförmigen Vorwölbung und progressiven Verdünnung der Hornhaut einhergeht. Neben Progredienzkontrolle und stabilisierenden Interventionen kommt der optischen Korrektur des Sehfehlers, verursacht durch eine meist sehr irreguläre Hornhautoberfläche, hinsichtlich Lebensqualität und Arbeitsfähigkeit große Bedeutung zu. Dieses Ziel kann effektiv und komplikationsarm durch Kontaktlinsen erreicht werden. Diese Arbeit gibt einen aktuellen Überblick über die Kontaktlinsenanpassung beim Keratokonus und informiert über eigene Auswertungen zu diesem Thema.AbstractKeratoconus is a non-inflammatory corneal disease associated with a cone-shaped protrusion and progressive corneal thinning. Apart from progression control and stabilizing interventions, correcting the optical error induced by a mostly highly irregular corneal surface is of paramount importance with respect to quality of life and ability to work. This goal can be achieved efficiently by contact lenses with only rare adverse conditions. This article provides a current overview on contact lens fitting in keratoconus and presents own associated results.

Asymmetry between Left and Right Eyes in Keratoconus Patients Increases with the Severity of the Worse Eye

ABSTRACT Purpose: To evaluate whether the inter-eye asymmetry of keratoconus (KC) patients is different from a healthy control group and to investigate how asymmetry changes with increasing severity of the disease. Methods: In this retrospective study, we included both eyes of 350 patients with KC (age 35 ± 13 years) and 68 candidates planned for refractive surgery (control group, age 37 ± 11 years). Inclusion criteria for the KC group were keratoconus in at least one eye with Pentacam Topographical Keratoconus Classification (TKC) of at least 0.5. Patients eligible for refractive surgery in both eyes were included in the control group. Corneal tomography as well as Ocular Response Analyzer measurements were compared between both groups. Subgroup analysis was performed with respect to the TKC staging. Asymmetry was provided as worse eye (defined by higher TKC) minus fellow eye. Results: In the KC group, both eyes showed the same TKC staging in 30.6%, a difference of one stage in 34.0% and of two stages in 24.6% of the patients. The inter-eye asymmetry in the keratoconus group was significantly larger than that in the control group. Corneal power showed an asymmetry of 3.8 ± 4.0 D in keratoconus eyes versus 0.22 ± 0.17 D in the control group. Central corneal thickness (CCT) asymmetry was 34 ± 30 µm versus 6 ± 5 µm, respectively. The Keratoconus Match Index showed an asymmetry of 0.40 ± 0.35 versus 0.15 ± 0.14. The difference between both eyes increased with increasing TKC of the worse eye. Conclusions: Inter-eye asymmetry is larger in keratoconus than in normal eyes, and it increases with keratoconus severity in the worse eye.