Measuring intraocular pressure (IOP) is the cornerstone of a comprehensive glaucoma examination. In babies or small children, however, IOP measurements are problematic, cannot often be performed at the slit lamp, and sometimes require general anesthesia. Therefore, it is essential for an ophthalmologist who examines a pediatric patient to be aware of the different tonometers used in children, as well as the effects of central corneal thickness and anesthesia on IOP measurements. Goldmann applanation tonometry is the gold standard for IOP assessment. Most alternative tonometers tend to give higher IOP readings than the Goldmann applanation tonometer, and readings between different tonometers are often not interchangeable. Similar to Goldmann tonometry, many of these alternative tonometers are affected by central corneal thickness, with thicker corneas having artifactually high IOP readings and thinner corneas having artifactually lower IOP readings. Although various machines can be used to compensate for corneal factors (e.g., the dynamic contour tonometer and ocular response analyzer), it is important to be aware that certain ocular diseases can be associated with abnormal central corneal thickness values and that their IOP readings need to be interpreted accordingly. Because induction and anesthetics can affect IOP, office IOPs taken in awake patients are always the most accurate.

Abstract Purpose: To determine if inter-eye asymmetry of a three-dimensional neuroretinal rim parameter, the minimum distance band, is useful in differentiating normal from open-angle glaucoma eyes. Materials and Methods: This is a cross-sectional study. Both eyes of 28 normal subjects 33 glaucoma subjects were analyzed. Subjects underwent spectral domain optical coherence tomography imaging of both eyes. A custom-designed segmentation algorithm calculated mean minimum distance band neuroretinal rim thickness globally, for four quadrants and for four sectors. Inter-eye minimum distance band thickness asymmetry was calculated as the absolute difference in minimum distance band thickness values between the right and left eyes. Results:  Increasing minimum distance band thickness asymmetry was not associated with increasing age or increasing refractive error asymmetry. Glaucoma patients had thinner mean neuroretinal rim thickness values compared to normal patients (209.0 μm versus 306.0 μm, P < 0.001). Glaucoma subjects had greater inter-eye thickness asymmetry compared to normal subjects for the global region (51.9 μm versus 17.6 μm, P < 0.001) as well as for all quadrants and all sectors. For detecting glaucoma, a thickness asymmetry value greater than 28.3 μm in the inferior quadrant yielded the greatest sum of sensitivity (87.9%) and specificity (75.0%). Globally, thickness asymmetry greater than 30.7 μm yielded the greatest sum of sensitivity (66.7%) and specificity (89.3%).  Discussion: This study indicates that inter-eye neuroretinal rim minimum distance band asymmetry measurements, using high-density spectral domain optical coherence tomography volume scans, may be an objective and quantitative tool for the evaluation of open-angle glaucoma patients.

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