This allows the researcher to assess the prevalence of a disease or of other variables of interest. The methods can be standardized by the researcher, and clear-cut definitions can be applied to the exposure and the endpoints.
This article has been corrected. See Indian J Ophthalmol. This article has been cited by other articles in PMC. Observational cross-sectional series from the comprehensive clinic of a tertiary eye care center seen during December Patients with high refractive errors, recent surgeries, glaucoma, and corneal disorders were excluded so as to rule out patients with evident altered corneal biomechanics.
Linear regression and Bland—Altman using MedCalc software. Intraclass correlation coefficient for repeatability ranged from 0.
However, agreement between the devices was statistically insignificant, and no influence Contour cross sectional report sequence was observed.
Many novel methods of measuring the IOP have been devised. This is based on the principle that by surrounding and matching the contour of the cornea, the pressure on the outside matches the pressure on the inside. IOP measured by GAT on an average has been noted to be lower than that measured by the DCT as it is considered to be less affected by corneal biomechanical properties and maintains the natural shape of the cornea during measurement.
OPA of glaucoma patients can vary significantly from that of normal patients. The unique features of the Corvis ST are that it provides a two-dimensional image of a cross-section of the deforming cornea during applanation, measures the apical displacement of the cornea and also measures the IOP.
To further distinguish the contrasting effects on repeatability of IOP measurements, we have measured the IOP in each patient in four different sequences of measurement by the different devices. The hypothesis was that noncontact methods of measurement using an air-puff may introduce some form of residual deformation in the cornea due to its viscoelastic nature, which may affect the subsequent IOP measurements when the devices are used sequentially.
Methods This was an observational cross-sectional study performed on patients of comprehensive clinic of a tertiary eye care center located in Southern part of India after approval by the Institutional Review Board in December Informed consent was obtained from all the subjects, and the study adhered to the tenets of the declaration of Helsinki.
The sample size was calculated based on a pilot study assuming Type 1 error of 0. Both eyes of the patients were tested but only one eye the right eye of each patient was included in the study to eliminate bias, and the patients on whom all the tests could not be performed were excluded from analysis.
Both the eyes of patients were examined, and IOP was estimated with all four instruments. Of these, for four patients, DCT could not be estimated with appropriate reliability, and for three patients, GAT could not be performed for logistic reasons.
Hence, the right eyes of subjects were included in the study. The patients with cataract and pseudophakia that were operated more than a year ago were included. This was done to eliminate any factors that would have affected the corneal biomechanical properties significantly.
Similarly, the patients with altered corneal biomechanics: Patients in whom subclinical corneal ectatic conditions or keratoconus was suspected based on refraction and clinical findings were subjected to pentacam and were excluded from the study if it showed significant abnormality.
There was a gap of 5 min between each measurement on a machine. The machines can be classified into two groups: The dynamic measurement is due to the high-pressure air-puff applied on the cornea to quantify corneal biomechanics in addition to IOP measurement. There is a possibility of residual effect of applanation or air puff on subsequent IOP measurements, hence to eliminate the bias we chose four different sequences, i.
Although, with four devices, there are 24 sequences possible but that would make the study very complex; hence, we limited ourselves to four sequences. The patients were randomly assigned to one of the four sequences. To eliminate diurnal variations in IOP, all measurements were completed in one visit of the patient and no follow-up measurements were needed.
These four sequences were as follows: Linear regression was performed between the mean values of IOPs for each patient from a device and the correlation coefficient along with the lack of fit was analyzed.
Similarity of the devices was compared with Bland—Altman plots for repeated measures. Intraclass correlation coefficient repeated measures and interobserver different devices variability coefficient of variation were also evaluated for all the devices. All tests used a P value of 0.
Results The right eyes of subjects were included in the study, out of which 25 were normal volunteers and were patients who presented to the outpatient department.
There were 57 males and 68 females. Table 1 lists the median values of all measurements taken by different devices. The coefficient of variation was 3.
Even though IOPg was supposed to be Goldmann-correlated, the present patient group did not demonstrate high coefficient of correlation.Sep 03, · A step by step explanation on how to draw a cross section.
You would use a topographic map with contour lines for this. Don't forget to watch my other Geogra. Cross contour lines are drawn lines which travel, as the name suggests, across the form.
Cross contours may be horizontal or vertical, as on the right side of the example, or both. Often, in more complex forms, cross-contours will be drawn at varying angles. Using NFIP Studies and Maps Figure is a representation of the description of cross-section A given in Table 6.
Figure Representation of cross-section A of the Rocky River. Velocity Contour Weighting Method. I: Algorithm Development and Laboratory Testing Daniel J. Howes and Brett F. Sanders. Abstract: An algorithm is developed for real-time estimation of the cross-sectional average velocity of a channel flow by using an upward-.
Things to note about contour maps and cross-sections: • When contours are close together - the slope is steep.
• When contours are wide apart - the slope is slight. In this method cross-sectional points are taken at regular interval. By levelling the reduced level of all those points are established. The points are marked on the drawing sheets, their reduced levels (RL) are marked and contour lines interpolated.