Abstract
Purpose::
To develop a new device for testing near visual acuity parameters (with or without distance and/or near correction), such as reading acuity, reading speed and critical print size under maximally standardized conditions.
Methods::
In most clinical studies concerned with the outcome of surgical procedures - e.g. different means of correction for presbyopia -, reading acuity is one, if not the main target. A comparison between different centres can only performed with adequate testing methods and meticulous standardization which are very difficult to achieve. A device for testing near visual acuity under very standardized circumstances is clearly needed to be able to objectively compare results in different studies. Based on the "Radner-Reading-Charts", we developed the SRD for testing near visual acuity (reading acuity, reading speed and critical print size) under standardized illumination. The reading distance - by far the most critical parameter in testing near visual acuity - seems to be quite variable for every patient tested, when trial subjects are allowed to freely choose a subjectively convenient distance. Thus measuring near visual acuity at a given, fixed distance does not allow one to draw conclusions on the "every day reading ability" of the patients. Therefore the continuously changing reading distance is also continuously monitored by stereo-photometry, using two different ip-cameras and is mathematically taken into consideration. The reading angle, an additional variable parameter, can be chosen freely and adjusted by the patient, to offer the most convenient testing conditions.
Results::
Testing for validity and reliability has been performed with 2184 single measurements in distances between 16 and 63 cm, and reading angles between 0° and 40°. Based on the Radner Reading Charts an error range between logRad 0,004 at 63 cm and logRad 0,016 at 16 cm has been found (this amount is of no clinical relevance).
Conclusions::
With this standardized device it is possible to obtain objective, valid and comparable results as far as the true "reading abilities" of trial subjects are concerned. This encompasses reading acuity, reading speed and critical print size. Studies testing near visual acuity following several surgical methods (e.g. with multifocal IOLs, new laser ablation profiles or corneal implants) are currently initiated in Salzburg with the use of the SRD in order to firmly establish the validity of this refined method for near visual acuity evaluation.
Keywords: clinical research methodology • presbyopia • visual acuity