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Turki M Almubrad - One of the best experts on this subject based on the ideXlab platform.
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comparison of the precision of the topcon sp 3000p Specular Microscope and an ultrasound pachymeter
Clinical Ophthalmology, 2011Co-Authors: Turki M Almubrad, Uchechukwu L Osuagwu, Ibrahim Alabbadi, Kelechi C OgbuehiAbstract:Aim: To compare the precision of the Topcon SP-3000P noncontact Specular Microscope (NCSM) and the DGH 500 ultrasound pachymeter (USP).
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limits of agreement between the optical pachymeter and a noncontact Specular Microscope
Cornea, 2005Co-Authors: Kelechi C Ogbuehi, Turki M AlmubradAbstract:PURPOSE To determine the limits of agreement between central corneal thickness (CCT) measurements made with the slit lamp-attached optical pachymeter and the SP2000P noncontact Specular Microscope. METHODS Triplicate readings for CCT were obtained for each of 130 (right) eyes of 130 patients, using the slit lamp-attached optical pachymeter and then the SP2000P noncontact Specular Microscope. The average CCT measured by each method was compared. Subsequently, the mean difference between both sets of measurements was assessed, and the 95% confidence interval (limits of agreement) between both techniques was determined. RESULTS The mean +/- SD CCT measured by the optical pachymeter was 543 +/- 34 microm and 532 +/- 34 microm for the Specular Microscope. We found a statistically significant (P < 0.001) mean bias of 10 mum between CCT values measured with both types of equipment, with the optical pachymeter returning the higher values. The coefficient of variation was 6.3% for the optical pachymeter and 6.4% for the Specular Microscope. CONCLUSIONS The right eye CCT measurements made by the optical pachymeter are, on average, 10 mum thicker than those made with the SP2000P Specular Microscope, which suggests that both pieces of equipment cannot be used interchangeably to monitor CCT changes in patients. Excluding left eye measurements, the reliability of the optical pachymeter is identical to that of the noncontact Specular Microscope.
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repeatability of central corneal thickness measurements measured with the topcon sp2000p Specular Microscope
Graefes Archive for Clinical and Experimental Ophthalmology, 2005Co-Authors: Kelechi C Ogbuehi, Turki M AlmubradAbstract:The non-contact Specular Microscope has become the method of choice for a quick, accurate and non-invasive assessment of central corneal thickness (CCT), which is an important variable to monitor before and after refractive surgery. The consistency of the results produced by such widely used methods/equipment must be assessed to determine their reliability. The purpose of this study was to assess within- and between-observer repeatability of, and to determine if a systematic bias exists in the measurements made by, the Topcon SP2000P Specular Microscope. The CCT of the right eyes of 70 adult subjects, divided equally between men and women, was assessed on two separate occasions (4–7 days apart) by each of two examiners using the low-intensity auto mode of the SP2000P Specular Microscope. The average CCT values for men and women, measured by one observer, were 0.52±0.03 mm (mean ± SD) and 0.52±0.04 mm, respectively. The average for the entire sample was 0.52±0.04 mm. Within- and between-observer repeatability were assessed by plotting the mean difference (for each subject) between two readings made by the same observer or one each by both observers against the combined average CCT reading of both sessions; the mean difference between two sets of observations was not significantly different from zero (P<0.05). For the first observer, the 95% limits of repeatability were between −0.015 and 0.017 mm. For the second observer, the 95% limits of repeatability were between −0.018 and 0.018 mm. For the between-observer repeatability, the 95% limits of agreement were between −0.016 and 0.016 mm. For both within- and between-observer repeatability, we found no systematic bias of the mean difference with the average CCT reading. The within- and between-observer limits of agreement we found were similar to those previously reported for the Topcon SP2000P Specular Microscope; the range of the 95% limits of repeatability were within ±1 SD of the average CCT reading for both sessions. We suggest that a technique be considered reliable if: (1) the mean difference between two measurements does not vary significantly from zero, (2) there is no systematic bias of the mean difference with the magnitude of the measured quantity and (3) the error inherent in a measurement technique is within ±1 SD of the average measurement of the two sessions.
Kelechi C Ogbuehi - One of the best experts on this subject based on the ideXlab platform.
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evaluation of the comparative effect of tetracaine on central corneal thickness measured by a contact and noncontact pachymeter
Journal of Ocular Pharmacology and Therapeutics, 2013Co-Authors: Uchechukwu L Osuagwu, Kelechi C OgbuehiAbstract:Abstract Purpose: To compare the effect of tetracaine 1% on central corneal thickness (CCT) measurements obtained by the ultrasound pachymetry (USP) and Topcon SP-3000P Specular Microscope. Methods: In the following sequence, SP-3000P before anesthesia, USP before anesthesia, SP-3000P 10 mins after anesthesia, USP 10 mins after anesthesia, CCT measurements were obtained from 100 randomly selected eyes of 50 oculo-visually young adults in 2 measurement sessions. Results: The CCT before instilling anesthetic did not vary significantly in each technique within session (P>0.05) and between sessions (P>0.05). Baseline CCT measurements obtained by the USP were significantly (P 0.05) was observed 10 mins after instilling one drop of 1% tetracaine in both sessions of SP-3000P, whereas a statistically significant increase (P<0.05) in CCT in both sessions of USP...
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comparison of the precision of the topcon sp 3000p Specular Microscope and an ultrasound pachymeter
Clinical Ophthalmology, 2011Co-Authors: Turki M Almubrad, Uchechukwu L Osuagwu, Ibrahim Alabbadi, Kelechi C OgbuehiAbstract:Aim: To compare the precision of the Topcon SP-3000P noncontact Specular Microscope (NCSM) and the DGH 500 ultrasound pachymeter (USP).
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limits of agreement between the optical pachymeter and a noncontact Specular Microscope
Cornea, 2005Co-Authors: Kelechi C Ogbuehi, Turki M AlmubradAbstract:PURPOSE To determine the limits of agreement between central corneal thickness (CCT) measurements made with the slit lamp-attached optical pachymeter and the SP2000P noncontact Specular Microscope. METHODS Triplicate readings for CCT were obtained for each of 130 (right) eyes of 130 patients, using the slit lamp-attached optical pachymeter and then the SP2000P noncontact Specular Microscope. The average CCT measured by each method was compared. Subsequently, the mean difference between both sets of measurements was assessed, and the 95% confidence interval (limits of agreement) between both techniques was determined. RESULTS The mean +/- SD CCT measured by the optical pachymeter was 543 +/- 34 microm and 532 +/- 34 microm for the Specular Microscope. We found a statistically significant (P < 0.001) mean bias of 10 mum between CCT values measured with both types of equipment, with the optical pachymeter returning the higher values. The coefficient of variation was 6.3% for the optical pachymeter and 6.4% for the Specular Microscope. CONCLUSIONS The right eye CCT measurements made by the optical pachymeter are, on average, 10 mum thicker than those made with the SP2000P Specular Microscope, which suggests that both pieces of equipment cannot be used interchangeably to monitor CCT changes in patients. Excluding left eye measurements, the reliability of the optical pachymeter is identical to that of the noncontact Specular Microscope.
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repeatability of central corneal thickness measurements measured with the topcon sp2000p Specular Microscope
Graefes Archive for Clinical and Experimental Ophthalmology, 2005Co-Authors: Kelechi C Ogbuehi, Turki M AlmubradAbstract:The non-contact Specular Microscope has become the method of choice for a quick, accurate and non-invasive assessment of central corneal thickness (CCT), which is an important variable to monitor before and after refractive surgery. The consistency of the results produced by such widely used methods/equipment must be assessed to determine their reliability. The purpose of this study was to assess within- and between-observer repeatability of, and to determine if a systematic bias exists in the measurements made by, the Topcon SP2000P Specular Microscope. The CCT of the right eyes of 70 adult subjects, divided equally between men and women, was assessed on two separate occasions (4–7 days apart) by each of two examiners using the low-intensity auto mode of the SP2000P Specular Microscope. The average CCT values for men and women, measured by one observer, were 0.52±0.03 mm (mean ± SD) and 0.52±0.04 mm, respectively. The average for the entire sample was 0.52±0.04 mm. Within- and between-observer repeatability were assessed by plotting the mean difference (for each subject) between two readings made by the same observer or one each by both observers against the combined average CCT reading of both sessions; the mean difference between two sets of observations was not significantly different from zero (P<0.05). For the first observer, the 95% limits of repeatability were between −0.015 and 0.017 mm. For the second observer, the 95% limits of repeatability were between −0.018 and 0.018 mm. For the between-observer repeatability, the 95% limits of agreement were between −0.016 and 0.016 mm. For both within- and between-observer repeatability, we found no systematic bias of the mean difference with the average CCT reading. The within- and between-observer limits of agreement we found were similar to those previously reported for the Topcon SP2000P Specular Microscope; the range of the 95% limits of repeatability were within ±1 SD of the average CCT reading for both sessions. We suggest that a technique be considered reliable if: (1) the mean difference between two measurements does not vary significantly from zero, (2) there is no systematic bias of the mean difference with the magnitude of the measured quantity and (3) the error inherent in a measurement technique is within ±1 SD of the average measurement of the two sessions.
Yann Gavet - One of the best experts on this subject based on the ideXlab platform.
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Digitalization of a Wide Field Contact Specular Microscope
IRBM, 2016Co-Authors: G. Hor, Yann Gavet, Philippe Gain, Claudio Urrea, Alfred Bernard, Gilles ThuretAbstract:Objectives: Non-contact Specular Microscopes (SM) have a very small field of observation (usually 0.1 mm2). This constitutes a major limitation when accurate and extended assessment of the corneal endothelium is needed, for instance during clinical trials or difficult diagnosis. Previous contact SM had the advantage of a wide field thanks to the use of an applanating cone but none of the old commercial devices passed the stage of digitalization. This paper aims at upgrading a wide field contact SM with a digital camera and dedicated software in order to combine wide field with the advantages of non-contact SM.Materials and methods: The digital device was composed of an acquisition unit consisting in a contact Konan Specular SP5500 equipped with a digital camera Canon EOS 6D and a Linux-based computer. Image processing uses segmentation algorithms (Gestalt theory and watershed with markers).Results: The device acquired wide field (0.5 mm2) highly contrasted images. The software provided cell boundaries and statistics: endothelial cell density, coefficient of variation of cell area and percentage of hexagonality. Contact SM images significantly increased the sampling of endothelial cells and consequently the reliability of endothelial quality analysis.Conclusion: The digital contact SM is not destined to compete with commercial non-contact SM but is an exceptional device for reference centers. It will allow obtaining accurate and reproducible endothelial qualification for specific studies.
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Comparison and supervised learning of segmentation methods dedicated to Specular Microscope images of corneal endothelium
International Journal of Biomedical Imaging, 2014Co-Authors: Yann Gavet, Jean-charles PinoliAbstract:The cornea is the front of the eye. Its inner cell layer, called the endothelium, is important because it is closely related to the light transparency of the cornea. An in vivo observation of this layer is performed by using Specular microscopy to evaluate the health of the cells: a high spatial density will result in a good transparency. Thus, the main criterion required by ophthalmologists is the cell density of the cornea endothelium, mainly obtained by an image segmentation process. Different methods can perform the image segmentation of these cells, and the three most performing methods are studied here. The question for the ophthalmologists is how to choose the best algorithm and to obtain the best possible results with it. This paper presents a methodology to compare these algorithms together. Moreover, by the way of geometric dissimilarity criteria, the algorithms are tuned up, and the best parameter values are thus proposed to the expert ophthalmologists.
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assessment of the human corneal endothelium in vivo topcon sp2000p Specular Microscope versus ex vivo sambacornea eye bank analyser
British Journal of Ophthalmology, 2007Co-Authors: Gilles Thuret, Nilanjana Debjoardar, C Manissolle, M Zhao, Michel Peoch, P Gain, Yann GavetAbstract:Comparison between assessment of donor tissue in eye banks and Specular microscopy in the recipient is important to quantify the post-keratoplasty cell loss dynamics. Our aim was to determine the agreement between the in vivo non-contact Specular Microscope Topcon SP2000P and the computer-assisted eye bank endothelial analyser Sambacornea. We enrolled 51 future recipients of penetrating keratoplasty, and determined the endothelial cell density (ECD) and morphometry firstly in vivo with Topcon and then ex vivo with Sambacornea on the excised cornea stained with Alizarin Red. Specular microscopy was found to underestimate the ECD by 11%, (95% CI 6 to 15), whereas morphometric parameters did not differ. Endothelial cell loss after penetrating keratoplasty is commonly evaluated by non-contact Specular microscopy. A comparison of tissue assessment in eye banks and that by Specular microscopy in the recipient is important to quantify the postoperative cell loss dynamics. In Europe, where organ culture is common, preoperative endothelial cell density (ECD) is assessed either by manual counting by observation through a Microscope reticule or by using computer-assisted analysers.1– …
Thomas Olsen - One of the best experts on this subject based on the ideXlab platform.
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optical principles for estimation of endothelial cell density with the non contact Specular Microscope
Acta Ophthalmologica, 2009Co-Authors: Thomas OlsenAbstract:In non-contact Specular microscopy of corneal endothelium, endothelial cell density is overestimated due to the angle of observation and the curvature of cornea. On the basis of theoretical considerations, it is concluded that if the angle of observation is kept at a small value the curvature of cornea contributes only insignificantly to this overestimation, the major determinant being the angle of observation. When an angle of 46 degrees is chosen between slit illumination and optical axis of the Microscope it is calculated that estimates of endothelial cells should be multiplied with a factor of 0.959 to correct for the angle effect. Six eye were photographed with both a contact and non-contact Specular Microscope and endothelial cell density estimated. Mean observed difference in cell counts was +5.5% without correction and +1.2% with correction for angle effect. 95% confidence limits for the difference with correction were -3.7 and +6.0% respectively showing that estimates of endothelial cell density obtained with the non-contact Specular Microscope agree closely with those obtained by contact Specular microscopy when corrected for angle of observation.
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changes in the corneal endothelium after acute anterior uveitis as seen with the Specular Microscope
Acta Ophthalmologica, 2009Co-Authors: Thomas OlsenAbstract:In order to investigate whether inflammation of the anterior uveal tract is accompanied by a loss of endothelial cells, 13 patients with previous unilateral attacks of anterior uveitis were photographed with the non-contact Specular Microscope. All patients had shown an increased thickness or frank oedema of the cornea during the acute phase of the inflammation. As compared to the healthy eye, only two patients (15%) showed endothelial cell densities on the affected side which were lower than was to be expected from the normal difference between counts from left and right eye in a control population of 36 subjects. The two patients with detectable cell loss also showed defects in the Specular reflex, the significance of which is discussed.
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influence of tranexamic acid and acetylsalicylic acid on the thickness of the normal cornea
Acta Ophthalmologica, 2009Co-Authors: Thomas Olsen, Niels Ehlers, Thorkild BramsenAbstract:In a masked cross-over study ten normal subjects were treated with tranexamic acid and acetylsalicylic acid one g three times daily for seven days. The central corneal thickness. was found to increase in response to acetylsalicylic acid and to decrease in response to tranexamic acid. This finding provides evidence for the involvement of the fibrinolytic system in the regulation of the normal corneal thickness. The endothelial morphology, as seen with the Specular Microscope, was unchanged during treatment with either drug.
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non contact Specular microscopy of human corneal endothelium
Acta Ophthalmologica, 2009Co-Authors: Thomas OlsenAbstract:: The non-contact Specular Microscope enables a large area of the corneal endothelium to be examined and photographed without any risk of traumatizing the anterior surface of cornea. This non-contact technique is described in detail. Standard deviation of the relative difference between two independent estimates of central endothelial density from 24 eyes was 3.7%. Standard deviation of the relative difference between counts from left and right eyes from 57 subjects was 4.7%. A significant negative correlation between age and endothelial cell density was found (r = -0.59, P less than 0.001, n = 76). The interindividual variation in cell densities was found to be larger in the old age group, indicating that cell loss during aging varies among different individuals.
Hikaru Hamano - One of the best experts on this subject based on the ideXlab platform.
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corneal thickness measurements with the topcon sp 2000p Specular Microscope and an ultrasound pachymeter
Archives of Ophthalmology, 1999Co-Authors: Renee Bovelle, Stephen C Kaufman, Hilary W Thompson, Hikaru HamanoAbstract:Objective To compare the reproducibility of measurements obtained with a new pachymetry instrument, the Topcon Specular Microscope (Topcon SP-2000P; Topcon America Corp, Paramus, NJ), with those obtained by ultrasound pachymetry. Methods Corneal thickness was measured in 40 eyes of 40 patients 3 times each with the Topcon SP-2000P and an ultrasound pachymeter (DGH 500; DGH Technology Inc, Exton, Pa) by 2 separate investigators. Comparisons included average thickness as measured by each instrument, average thickness for each instrument as measured by each investigator, and differences in thickness due to corneal abnormalities. Results Mean corneal thickness measured by the Topcon instrument was significantly less (32 µm; P P P =.32]) than those obtained with the ultrasound unit (difference was significant [ P =.02]). Conclusions The new noncontact Topcon Specular Microscope provides measurements of corneal thickness that are somewhat less than those of ultrasound pachymetry, but that seem to be more consistent from one operator to another, possibly as a result of the elimination of observer bias induced by probe placement required by the ultrasound unit. This consistency may be important in the comparison of measurements by different operators over time in patients being followed up after refractive surgery or other therapeutic interventions.