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Biomedical subjects

Christoph Kniestedt

Publications and source records attributed to Christoph Kniestedt.

12 recordsLinked to original sources
PubMed2006

A novel PITX2 mutation and a polymorphism in a 5-generation family with Axenfeld-Rieger anomaly and coexisting Fuchs' endothelial dystrophy.

PURPOSE: To investigate the clinical and genetic appearance of Axenfeld-Rieger anomaly or syndrome (ARAS) and Fuchs' endothelial dystrophy (FED) in a 5-generation pedigree coexpressing both pathologic features in a large number of family members. DESIGN: Observational case-control and DNA linkage and screening study. PARTICIPANTS: Of 114 family members, 50 underwent clinical investigation and DNA analysis between July 2001 and March 2004. METHODS: Linkage at the PITX2 locus was demonstrated using a number of microsatellites mapping to the critical region 4q25 to 4q26. The PITX2 gene was subsequently screened for mutations in all investigated family members. MAIN OUTCOME MEASURE: Linkage of the ARAS and FED phenotype and mutation detection in the PITX2 gene. RESULTS: Twenty-seven patients were identified as being affected by ARAS. Fuchs' endothelial dystrophy was found in 19 patients. Fifteen patients presented both kinds of anomaly. Deoxyribonucleic acid sequencing revealed 2 heteroallelic DNA variants that segregated together (on the same allele) and were present in all severely affected ARAS individuals. The first variant, g.20913G>T, assumed to be the causative mutation for ARAS, causes amino acid substitution at codon 137 (G137V). A statistically significant 2-point logarithm of the odds score of 4.06 was obtained with marker D4S406. The second variant is likely a polymorphism in the intron between exons 2 and 3 (IVS2+8delCinsGTT) and was detected in heterozygous form in 20% of control individuals. CONCLUSION: This gene analysis revealed a novel PITX2 mutation and a polymorphism in a family with ARAS. Whether FED, also manifested in the severely affected individuals, is due to a different but cosegregating gene is to be determined.

Adolescent↗
PubMed2006

Intraocular pressure and ocular pulse amplitude comparisons in different types of glaucoma using dynamic contour tonometry.

PURPOSE: To compare the intraocular pressures (IOP) and ocular pulse amplitudes (OPA) in patients with different types of glaucoma, ocular hypertension (OHT), and normal controls (NC) using dynamic contour tonometry (DCT) and the goldmann applanation tonometry (GAT). METHODS: 906 eyes of 501 adult patients in the following five groups were included in this cross-sectional study: primary open angle glaucoma (POAG), normal tension glaucoma (NTG), Pseudoexfoliative Glaucoma (PXG), OHT, and NC. The following tests were performed simultaneously during a single visit: IOP using DCT and GAT; OPA using DCT and central corneal thickness (CCT) using ultrasound pachymetry. Mixed effects regression models were used to compare the DCT and GAT IOP measurements in the five groups; the effect of CCT on IOP and the relationship between OPA and IOP within each group. RESULTS: DCT consistently had higher IOP values than GAT in POAG, PXG, NTG, and controls (p < 0.001) but not in OHT (p = 0.84). DCT IOP did not change while GAT IOP showed a non-significant increase (p = 0.09) with increased corneal thickness in each group. OPA was found to be highest in OHT (3.61 mmHg) and lowest in the control group (2.86 mmHg) and significantly increased with IOP in all groups. CONCLUSIONS: DCT measures an IOP that is significantly higher than GAT IOP in glaucoma and control subjects but not in ocular hypertensives. Furthermore, the DCT may measure an IOP that is independent of the CCT, which may not be true for the GAT, which increases with the CCT. OPA was highest in OHT and may be affected by the IOP.

Blood Pressure↗
PubMed2006

Correlation between intraocular pressure, central corneal thickness, stage of glaucoma, and demographic patient data: prospective analysis of biophysical parameters in tertiary glaucoma practice populations.

PURPOSE: To determine the correlation of central corneal thickness (CCT) to Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT, PASCAL), and to glaucoma stage as assessed by cup-to-disc ratio (CDR). DESIGN: Prospective, cross-sectional tricenter observation study. PATIENTS AND METHODS: From three glaucoma specialty practices a sample of 406 independent eyes was included. After ultrasound pachymetry, intraocular pressure was measured using PASCAL and Goldmann applanation tonometry and cup-to-disc ration was reassessed. Demographic data were included in the multivariate analysis. RESULTS: Mean corneal thickness was 540 microm. African Americans and normal-tension glaucoma patients showed the lowest values (518 microm and 522 microm, respectively). These values were significantly thinner than the central corneal thickness of Caucasians (549 microm) and ocular hypertensives (564 microm). Intraocular pressure assessed by Goldmann applanation tonometry shows a significant correlation with central corneal thickness (r = 0.068, P < 0.001), whereas PASCAL is not significantly associated with central corneal thickness (r < 0.001, P = 0.997). Increased IOP is significantly correlated with large ocular pulse amplitudes (r = 0.13, P < 0.001), which is predominantly seen in ocular hypertensives. A significant negative correlation was detected between cup-to-disc ratio and central corneal thickness (r = 0.102, P < 0.001). CONCLUSION: Glaucoma patients with thin central corneal thickness are more likely to be found at an advanced stage of the disease and among those with normal-tension glaucoma and black African ancestry. Underestimation of intraocular pressure by Goldmann applanation tonometry could be one causative factor.

Adolescent↗
PubMed2006

Dynamic contour tonometry: principle and use.

Interindividual variability of central corneal thickness has been found to be a source of error for conventional Goldmann applanation tonometry. The dynamic contour tonometer represents a potentially new technology for non-invasive and direct intraocular pressure (IOP) measurement, and has been proposed to accurately measure the true IOP irrespective of the corneal thickness. It is based on the principle that when the tip of the device exactly matches the contour of the cornea, the pressure measured by a transducer placed on its tip is an accurate indicator of the true IOP. This device is also capable of measuring the ocular pulse amplitude, a variable that has controversial significance in the diagnosis and management of glaucoma. Even though this technique seems to be very promising, further studies are required to conclusively determine the effectiveness of the dynamic contour tonometer in patients having an abnormal or irregular corneal contour.

Equipment Design↗
PubMed2005

Clinical comparison of contour and applanation tonometry and their relationship to pachymetry.

OBJECTIVES: To compare intraocular pressure readings of recently introduced dynamic contour tonometry (DCT) with pneumatonometry (PTG) and Goldmann applanation tonometry (GAT) and to correlate central corneal thickness (CCT) with these readings. DESIGN: Prospective, cross-sectional observation and instrument validation study. We included 258 independent eyes with normal anterior segment examinations results, irrespective of glaucoma diagnosis or glaucoma suspect. After pachymetry, DCT, PTG, and GAT were performed in a randomized order. Intraocular pressures as measured by DCT, PTG, and GAT were compared with each other and with CCT. RESULTS: Eyes with thinner CCTs tended to yield lower intraocular pressure measurements by GAT. A significant correlation (Pearson product moment correlation, P<.001) between CCT and GAT was found with a regression of 0.25 mm Hg per 10 microm (R2 = 0.060). Variation of CCT had no significant effect on intraocular pressure measurements by PTG (P = .10; R2 = 0.01) and DCT (P = .80; R2<0.01). A piecewise regression model showed that GAT readings are not linearly correlated with CCT. Comparison of the slopes below and above 535 microm showed the highest significance (P<.001). CONCLUSIONS: Goldmann applanation tonometry readings are potentially influenced by CCT, whereas PTG and DCT seem to be less dependent on CCT. Correlation between CCT and GAT is not linear. A simple correction formula suggesting a linear relationship might not be correct.

Adolescent↗
PubMed2005

Dynamic contour tonometry: presentation of a new tonometer.

PURPOSE: With tonometers currently in use intraocular pressure is indirectly determined by measuring a physical quantity related to a specified deformation of the cornea. We present a new principle of direct, continuous, and transcorneal intraocular pressure measurement, describe its theoretical foundation, and evaluate its application on the basis of an in vitro model. METHODS: On a living human eye an optimized pressure-sensitive contact surface was determined by performing pressure measurements with differently shaped tonometer heads. Based on these results and on the theoretical model, a Dynamic Contour Tonometer was constructed and validated on eye bank bulbi against a manometric reference pressure. RESULTS: A concave contact surface with a radius of curvature of 10.5 mm creates a distribution of forces between the central contour matching area of the tip and the cornea that equals the forces generated by the internal pressure of the eye. A sensor integrated into the surface having the same contour measures the intraocular pressure closely to the manometric reference pressure in human cadaver eyes. The accuracy of the tonometer appears to be unaffected by variations in corneal properties. CONCLUSION: Dynamic Contour Tonometry eliminates most of the systematic errors arising from individual changes of corneal properties that adversely influence all types of applanation tonometers. The advantage of measuring the true pressure in combination with the capability of registering dynamic pressure fluctuations discloses new tonometric opportunities to diagnose and classify different types of glaucoma.

Cornea↗
PubMed2004

Accuracy of dynamic contour tonometry compared with applanation tonometry in human cadaver eyes of different hydration states.

BACKGROUND: In an experimental laboratory investigation we compared intraocular pressure (IOP) measurements obtained by dynamic contour tonometry (DCT), Goldmann applanation tonometry (GAT), and pneumatonometry (PTG) with intracameral manometry on human cadaver corneas of different hydration conditions. METHODS: Ten freshly enucleated eyes were de-epithelialized. Two tubes were placed in the anterior chamber in opposite directions and connected to a transducer and to a bottle system filled with balanced salt solution. The pressure in the eye was then adjusted between 5 mmHg and 58 mmHg by electronically altering the height of the bottle. Central corneal thickness (CCT) was registered and IOP measurements were obtained with DCT, GAT, and PTG at each manometric pressure reading. Immediately after the trial the same corneas were artificially dehydrated and the same measurement regimen was repeated. RESULTS: In the pressure range defined by the bottle height 10-50 cm, IOP values measured by DCT were 0.50 mmHg (95% CI=0.40-0.60) and 0.36 mmHg (95% CI=0.25-0.47) higher than manometric readings before and after dehydration, respectively. GAT showed consistently lower values than manometry, the difference being -3.48 mmHg (95% CI=-3.91 to -3.05) and -3.14 mmHg (95% CI=-3.39 to -2.89), respectively. Similar results were obtained with PGT, namely differences of -4.75 mmHg (95% CI=-5.21 to -4.29) and -3.98 mmHg (95% CI=-4.48 to -3.48) for the hydrated and the dehydrated corneal condition, respectively. Only DCT showed no significant change in accuracy between hydrated and dehydrated corneas. CONCLUSIONS: In this in vitro study DCT values for IOP were significantly closer to the manometric reference pressure than those obtained using GAT and PTG, independent of the state of corneal hydration.

Aged↗
PubMed2004

Dynamic contour tonometry: a comparative study on human cadaver eyes.

OBJECTIVE: To compare intraocular pressure measurements obtained by recently introduced dynamic contour tonometry (DCT), Goldmann applanation tonometry (GAT), pneumatonometry (PTG), and intracameral manometry in human cadaver eyes. METHODS: Sixteen freshly enucleated human cadaver eyes were deepithelialized and dehydrated with dextran. A tube was placed in the anterior chamber and connected to a transducer and to a bottle system filled with balanced salt solution. The pressure in the eye was then altered between 5 mm Hg and 58 mm Hg. Intraocular pressure measurements were obtained with DCT, GAT, and PTG at each manometric pressure reading. RESULTS: On average, DCT values measured 0.58 +/- 0.70 mm Hg higher than real intracameral pressure. The GAT and PGT showed consistently lower values, -4.01 +/- 1.76 mm Hg and -5.09 +/- 2.61 mm Hg, respectively. At all bottle heights, DCT values were significantly closer to the reference pressure than GAT and PTG (P<.001). CONCLUSIONS: Measurement with DCT provides IOP values significantly closer to true manometric levels than either GAT or PTG. Further studies are warranted to determine its reliability in patients and the effect of corneal thickness.

Aged↗
PubMed2003

Visual acuity and its measurement.

Despite its critical importance to our daily life, the most common measurement of visual function, visual acuity, is a relatively crude and narrow one testing only a small portion of the broad range of visual functions. Visual acuity is the measurement of the ability to discriminate two stimuli separated in space at high contrast relative to the background. Clinically, this is measured by asking the subject to discriminate letters of known visual angle. The visual acuity is represented as the reciprocal of the minimal angle of resolution (the smallest letters resolved) at a given distance and at high contrast. Other measurements of visual acuity also exist, including Vernier acuity. Newer charts, such as the ETDRS chart, use letters of equal recognition difficulty and use the log of the minimal angle of resolution; these charts have significant advantages over the old Snellen-type charts. This article reviews visual measurements in children and in patients with low vision, and it reviews factors affecting visual acuity, such as pupil size, refractive error, media opacities, and pharmacologic agents.

Eye Diseases↗