EVIDENCE LEVEL I
Purpose: Figure 1 Figure 3
Portable automated perimetry devices play an important
role in glaucoma screening; by design they function
Duration of the examinations
reliably even outside of traditional eye clinics, reaching with CLIP and 4/2 strategies 4/2 CLIP
out, therefore, to an increased number of patients.
Moreover, they can be successfully used in regions with
poor medical coverage or in mobile screening stations. 6:00 OD CLIP
Our objective was to combine fast threshold examination 5:30 OD 4/2
strategies with an advanced software for interpreting 5:00
visual field data based on expert systems, while fully
maintaining the portability of the device. OS 4/2
To achieve our goal, CLIP (Continuous Light Increment 4:00 4
Perimetry) strategy and GSP (Glaucoma Staging 3:30
and Progression) software were for the first time 3:00 2
implemented on the hand control unit of the Oculus 2:30
Easyfield perimeter. This setup not only enables fovea centralis
shortened threshold examinations during glaucoma 20 25 30 35 40 45 50 55 60 65
screenings, but also offers a novel possibility to interpret the visual field data. With no further need of a dedicated
computer system, this setup provides us a portable device with extended glaucoma screening abilities.
Participants and methods of testing:
More about CLIP: From staircase to elevator
The visual field of 20 healthy eyes (10 OD, 10 OS) from 20 healthy test persons aged between 18 and 63 years (average
Figure 2 In the classical 4/2 strategy one starts by presenting light stimuli in 4 dB steps in the direction towards the threshold,
age 42.1 years, standard deviation 12.5 years) was tested using automated white on white perimetry. Only one eye
followed by 2 dB steps in the opposite direction after crossing the threshold. The measurement can be concluded after
of each patient was measured. Before the actual measurements all test persons executed a learning program on a
Comparing mean sensitivities the second crossing of the threshold. But, the method can lead to an increased number of sub-threshold stimuli in the
perimeter. In our study we used the 24-2 test pattern, each patient undergoing threshold examinations with both the
classical 4/2 strategy and CLIP. measured with CLIP and 4/2 strategies presence of defects. This often causes frustration of the patients.
34 CLIP (Continuous Light Increment Perimetry) follows a radically different path. In contrast to the regular bracketing
Results: OD CLIP methods, CLIP makes use of test points with luminance increased at a steady rate.
33 In the case of CLIP, the test stimulus is always “on”, its luminance being increased in time in smaller steps (usually
As a first result we report that the simultaneous implementation of a fast threshold strategy (CLIP) and of an advanced OD 4/2
Mean Sensitivity (dB)
1 dB), until the patient gives a positive answer. By measuring the average reaction time of the patient and choosing the
visual field data analysis software (Glaucoma Staging and Progression) on a truly portable perimeter was successful. 32
OS CLIP appropriate incremental rate of the luminance, a significant reduction of the examination time can be achieved, without
Examination time using CLIP was in average 2 min 37 sec, with a standard deviation of 21 seconds. The distribution of
losing precision or reproducibility.
individual values is presented in Fig. 1. The same plot presents the duration of the 4/2 threshold tests, with an average 31 OS 4/2
The fact that a stimulus with increasing luminance in the end is always perceived generates elevated patient comfort.
value of 5 min 50 sec and a standard deviation of 23 seconds.
In addition, we compared the values for mean sensitivities obtained using CLIP to the values for mean sensitivities Conclusions:
obtained using 4/2 threshold strategy. The values are presented in Fig. 2. One can easily notice that CLIP values are
Combining a modern fast threshold strategy (CLIP) and a sophisticated visual field data interpretation software (GSP)
slightly higher, the average difference of the mean sensitivities is 0.77 dB with a standard deviation of 0.41 dB. 28 is possible on a truly portable perimeter, in our case the Oculus Easyfield equipped with the hand control unit. With an
However, the correlation of the mean sensitivity values obtained with the two different methods underlines once again 20 25 30 35 40 45 50 55 60 65
average duration of 2 min 37 sec for a real measurement of threshold sensitivity values the speed of the examination
the reliability of the threshold measurements performed using CLIP on healthy subjects. Age (years) becomes comparable with the speed of usual supra-threshold tests. Good correlation with classical 4/2 threshold
All visual fields were analyzed with the newly implemented GSP (Glaucoma Staging and Progression) program.
measurement data strongly suggests high reliability of the results for healthy subjects. Obtaining reliable threshold
All examinations (100%) were assigned by the software to the Visual Field Class: Normal.
values in a considerably shortened time contributes to the expansion of the glaucoma screening abilities of the device.
For subjects with visual field defects further clinical studies are planned.
1. Lachenmayr, B., Vivell, P.M.O. (1992): Perimetrie, Thieme, Stuttgart
2. Wabbels, B., Burk, R. & Kolling, G. (2001): CLIP: an improved strategy in automated visual field testing. In: Wall, M. & Mills, R.P. (eds.): Perimetry Update 2000/2001. The Hague: Kugler 177-186
3. Wroblewski, D. et al. (2007) : Numerical Modelling of Visual Field Test Data for Glaucoma Detection and Evaluation, poster presented at the 2007 Meeting of ARVO