ABSTRACT: Pachymetry is important in relation to the intraocular pressure (IOP) and can either be contact measured or non-contact measured. Depending on the corneal thickness it is possible to get false IOP measurements up to +/-5 mmHg. Thus, it is necessary to know the exact corneal thickness. A new non-contact technique for measuring the corneal thickness is available with the Visante anterior segment optical coherence tomography (OCT, Zeiss).
Ultrasound as well as the OCT technique is based on beam reflection at optical interfaces. Ultrasound waves or, respectively, coherent light beams (electromagnetic waves) are used for the imaging. Twenty-six patients were examined using the OCT and ultrasound with special emphasis on the corneal thickness and the results compared.
The use of OCT to measure the corneal thickness is a safe method. Both techniques give comparable pachymetry results, whereas the OCT technique shows a tendency for lower values. Statistically significant differences could not be shown.
OCT is a new, non-contact technique for measuring the corneal thickness. Furthermore, this is a method that does not interact with other measurements like keratometry or corneal topography.
Klinische Monatsblätter für Augenheilkunde 12/2007; 224(11):832-6. · 0.51 Impact Factor
ABSTRACT: The purpose of the cataract surgery should be to guarantee the physiology of a young eye, especially with the ability to accommodate. This study focuses on accommodative changes in pseudophakic eyes.
Using the IOL Master (Carl Zeiss Jena), Scheimpflug camera EAS 1000 (Nidek) and Pupillograph (AMTech GmbH), detailed measurements of pseudophakic eyes for near and distance fixation were taken. The average age of all patients is 71 years.
With regard to the pseudophakic pupil movement a statistically significant decrease of the pupil size, for the light-influenced, and for the light-constricted pupil in near fixation could be shown. Furthermore, a statistically significant decrease of the pupil-constricting amplitude and a decrease of the reaction time after a light impulse was shown. Central vertical and horizontal corneal radii show significant increases with accommodation, which results in a decrease of the central corneal curvature. While reducing the anterior chamber depth, the pseudophakic eyes show a statistically significant minimising of the superior anterior chamber angle.
Pseudophakic accommodating eyes react similarly compared to the phakic accommodating eyes of young individuals.
Klinische Monatsblätter für Augenheilkunde 10/2007; 224(9):716-21. · 0.51 Impact Factor
ABSTRACT: The basics of the model of accommodation were described by Hermann von Helmholtz 150 years ago and are accepted until today.
Twenty-five healthy young phakic test persons (age range 14 to 28 years) were examined using the IOL Master (Carl Zeiss Jena GmbH), slit lamp photography (Scheimpflug camera EAS 1000, Nidek) and pupillography (AMTech GmbH). Measurements were taken of disaccommodated and accommodated eyes.
The mesopic and photopic pupil size are statistically significant (p < 0.05) smaller in accommodated eyes than in disaccommodated. Also, a significantly shorter reaction time of the light-induced pupil reaction with accommodation could be shown compared to disaccommodation. The central vertical and horizontal radii of curvature of the cornea increased with accommodation. This is likewise a decrease of the central anterior corneal curvature by near fixation. Due to the axial lens thickening, the anterior chamber angle and the anterior chamber depth decreased. Consequently, a decrease of the lens transparence resulted with accommodation.
As a result of our measurements the existing model of accommodation, developed by Hermann von Helmholtz 150 years ago, can be modified.
Klinische Monatsblätter für Augenheilkunde 08/2007; 224(8):653-8. · 0.51 Impact Factor