Higher order aberrations across the horizontal visual field
The relationship between higher order aberrations and position in the horizontal visual field is investigated in normal and refractive corneal surgery subjects. Individual aberration coefficients are ...
Interferometric measurements of dynamic changes of tear film
Tear film stability plays an important role in the quality of vision. We present an interferometric method for assessing the stability of precorneal tear film in real time. A lateral shearing techniqu...
Thecompensation comparison (CC) method is a psychophysical technique to measureretinal stray light. It uses a two alternative forced choice(2AFC) measurement paradigm. The 25 binary (0 and 1) responsesresulting from the 2AFC test are analyzed using maximum likelihoodestimates. The likelihood function is used to give two quantities:the most likely stray-light level of the eye under investigation,and the accuracy of this estimate [called expected standard deviation(ESD)]. The CC method is used in 2422 subjects ofthe GLARE study. Each eye is tested twice to allowanalysis of measurement repeatability. Furthermore, the large amount of responsesis used to evaluate the shape of the psychometric function,for which a mathematical model is used. The shape ofthe psychometric function found by averaging the 0 and 1responses fit well to the model function. Data sorted accordingto ESD show differences in the shape of the psychometricfunction between good and bad observers. These different shapes forthe psychometric function are used to reanalyze the data, butthe stray-light results remain virtually identical. ESD proves to bean efficient tool to detect unreliable measurements. In clinical practice,ESD may be used to decide whether to repeat ameasurement.
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