Practical guide for operating the Oculus C

Practical guide for operating the Oculus C
Practical guide for operating the
Oculus C-Quant straylight meter
(software version 1.09)
1
Introduction
This document is intended as help when working with the Oculus C-Quant straylight meter. It
gives some examples of possible measurement outcomes, which can be useful to interpret your
own results, especially when measurement reliability is not optimal. It is assumed that you are
already familiar with basic operation of the C-Quant. If not, please refer to the C-Quant
Instruction Manual.
Please start to familiarize yourself with the measurement by testing your own eye. Play with
different range settings (including “G”) and (erroneous) corrective lenses up till errors of + and 4D. Study the response patterns (lower graph of the C-Quant screen) obtained and compare them
with the examples in this document.
Startup and patient data entry (Patient Data Management screen)
-
Start up the C-Quant program by double clicking the Oculus Company logo on the desk
top. A screen-filling company logo appears. Click again to go to the Patient Data
Management screen.
Enter the appropriate patient data or select the appropriate patient from the patient list.
Note: the <First name> field needs at least two characters before the patient data can be
added to the patient list.
Start up the examination program by single clicking the [C-Quant] button. Note: Double
clicking will give an error!
If the message “C-Quant could not be found” appears, either the C-Quant is not switched
on, the C-Quant is not properly connected to the (laptop) computer, or the <Mode> setting
in the <System settings> dialog of the examination program (go to <Settings> <System>) does not correspond to the type of connection you are using (serial or USB).
After making the necessary adjustments, close down the examination program and start it
up again.
The examination program (Oculus C-Quant screen)
Before the measurement
Three settings need to be made on the screen before a measurement can be started:
1. Eye:
If both eyes are to be measured, start with the better/dominant eye. The other eye should be
occluded with an eye patch or something similar. Note: see under “Range” below.
2. Correction:
The refractive correction is not critical for the C-Quant measurement. A deviation of the best
corrected value of up to 2 diopters can easily be tolerated. Cylindrical errors of up to 3 diopters
may be corrected with the spherical equivalent. It is recommended to use only one trial lens for
refractive correction, unless the cylindrical correction is more than 3 diopters. Note: for visual
acuities down to 0.2, it should still be possible to perform the test. For visual acuities of 0.1 or
lower, the test will be very difficult to perform.
3. Range:
The default <Range> setting is “E(>75)”. This will be a proper setting in many cases, if straylight
increase is mild. If high straylight values are expected (e.g. with cataract or corneal turbidities),
settings “F(cataract)” or “G” must be used. “G” can also be used if you want an easy (first) test.
2
The response pattern obtained will guide you how to proceed. Note: change the <Range> setting
before changing the <Eye> setting, otherwise the <Eye> setting will jump back to “Left”. Note:
the chosen <Range> setting might turn out to be not optimal for the actual patient. Depending on
the circumstances, it might be necessary to repeat the measurement with a different <Range>
setting in order to obtain a (more) reliable measurement (see “After the measurement” below).
Patient instruction:
The instruction for the patient should include the following elements:
Eye position
- Position the eye close to the eyepiece, keeping a minimal distance (figure a). A slight
touch is good, but not firmly against it. If the eye is tightly against the eyepiece,
condensation may form on the lens of the C-Quant, which will influence the measurement
outcome (figure b). Also, if the eye is too far from the eyepiece, this will give a wrong test
result (figure c).
- Keep your eye normally open and do not squeeze, as this may also influence the
measurement outcome (figure d).
Task during the test
- Only concentrate on the two half fields in the center of the field; ignore the flickering
ring.
- Compare the two half fields, decide which one flickers more clearly/strongly, and press
the corresponding button on the C-Quant (left button if the left test field flickers stronger,
right button if the right test field flickers stronger). This procedure will be repeated for a
series of stimulus presentations, until the test is finished.
- React by first impression and react promptly. Do not try to think about a presentation. The
buttons can be pressed as soon as flicker appears, shortly after the beep.
- For several presentations, it will be hard to tell the difference between the two half fields
(they seem to be flickering equally strong). This is normal, and also here you must make a
choice following your first impulse.
- Optional information (only if the patients asks): one measurement consists of about 25
presentations and usually takes 1.5 to 2 minutes.
Make sure the patient is seated comfortably and the measurement takes place in a quiet
environment with a minimum of background noise and other people around. The measurement
requires full attention from the patient.
Start the measurement by clicking the [Start] button. A <Start Examination> dialog appears
where you can check if you entered the correct <Eye> and <Correction> settings. This
information must be correct, as it can not be altered afterwards. The settings can be altered in the
dialog box.
Click the [OK] button to start the actual measurement.
3
During the measurement
If the patient is too hesitant to choose between the two half fields and/or refuses to press a button,
you can enter responses yourself with the arrow keys on the computer/laptop. If you need to
generate a random answer (in case the patient is undecisive with respect to the left/right choice),
it is best to always press the same key (e.g. the left arrow key). Use this option cautiously.
After the measurement
When the measurement is finished, reliability is automatically verified. The measurement is
considered reliable when esd0.08 and Q1. In this case, both numbers are shown in black
(Example 1).
When esd>0.08 and/or Q<1, these values are shown in red, and the message “Reliability not
optimal. Consider to repeat the measurement” appears. What to do in such a case? This depends
on the actual value of esd. The reliability requirements employed in the C-Quant are rather strict.
In most clinical cases, measurements with esd0.1 or even esd0.12 are sufficiently reliable,
even ignoring the Q value (Example 2). To really get the best out of the measurement, you could
consider to repeat the measurement in order to obtain a measurement with esd0.08. Before
repeating the measurement, you should verify if a correct <Range> setting was chosen (see
below).
If esd>0.12, the measurement should be considered not reliable (but see below). The
measurement should be replaced to obtain a measurement with esd0.12. Again, you should first
verify if a correct <Range> setting was chosen (see below).
If reliability does not improve, the test may be too difficult for the patient (e.g. because of very
low visual acuity). In this case, the “G” setting for <Range> may help. The “G” setting is the
easiest for everybody, and should be used for difficult cases.
If esd>0.12 using a high <Range> setting (e.g. “G”), the result might still contain valuable
information. For many clinical applications, it is not necessary to know the exact straylight value,
but only whether or not the value is increased. In some cases, this information can be deduced
from a measurement, even if esd>0.12 (Examples 3a, 3b, and 3c).
When it is desirable to know the exact straylight value (e.g. for follow-up measurements) after
performing the test with the “G” range, another attempt could be made to obtain a reliable
measurement at the patient’s proper <Range> setting (the patient might have improved his
performance after performing the test with the “G” range).
When to choose a different <Range> setting?
The <Range> setting might be too high if the straylight value of the patient is low. In this case,
there are too many 1 responses and not enough 0 responses (Example 4). The <Range> setting
might be too low if the straylight value of the patient is much increased. In this case, there are too
many 0 responses and not enough 1 responses (Example 5). In both cases, repeating the
measurement with the same <Range> setting will not yield a lower esd value. You can only
improve reliability by choosing a different <Range> setting. Note: It is not always clear if the
chosen range was too low (Example 6). In such a case it is anyway a good idea to choose a
higher <Range> setting, because the test will be easier to perform then. Example 7 shows that
the patient from Example 6 is perfectly able to do the measurement. The chosen range in
Example 6 was apparently too low.
4
C-Quant Examples
Example 1: esd0.08 and Q1.
This is a reliable measurement. Note that there is almost no overlap between the 0 and 1
responses. More overlap means a less reliable measurement.
Example 2: 0.08<esd0.12.
Although reliability is not optimal, this measurement may be accepted as a good measurement in
most cases. However, if time allows, it is recommended to repeat the measurement in order to
obtain a better reliability. Note that there is quite some overlap between the 0 and 1 responses.
5
Example 3a: esd>0.12 in “G” range
If there is no time to repeat the measurement, this measurement can be used to estimate an upper
limit for the straylight value. Because there is a consistent row of 1 responses in the right part of
the graph, it is quite certain that the patient does not have a straylight value higher than the
outcome of the measurement. If you need a more reliable straylight value, just repeat the
measurement.
Example 3b: esd>0.12 in “G” range
This example is similar to Example 3a: if there is no time to repeat the measurement, the outcome
of this measurement can be used to estimate an upper limit for the straylight value. If you decide
to repeat the measurement, the surplus of 1 responses would suggest choosing a lower <Range>
setting (as in Example 6), but the presence of some erroneous points (blue points at 2.0, 2.3 and
3.3) indicates that this patient has difficulties to perform the test. Note that the same <Range>
setting (“G”) is the easiest for the patient.
6
Example 3c: esd>0.12 in “G” range
This example is similar to Examples 3a and 3b, only esd is so high that no estimation for the
straylight value could be calculated (log(s)=6.00 is a meaningless value). However, you can make
this estimation yourself by looking at the 1 and 0 responses: the 50%-point of the curve will
probably be not higher than 1.8, corresponding to a straylight value of 1.5, a moderately
increased value.
Example 4: <Range> setting too high
This measurement went very well, only there are too many 1 responses and not enough 0
responses for a reliable estimation of the straylight value. Reliability can be improved by
repeating the measurement at a lower <Range> setting.
7
Example 5: <Range> setting too low
There are too many 0 and not enough 1 responses for a reliable estimation of the straylight value.
The measurement reliability can be improved by repeating the measurement at a higher <Range>
setting (which will be “G” in this case).
Example 6: unreliable measurement at low <Range> setting
From this result you can not tell if the <Range> setting was chosen too low, or if the test is too
difficult for the patient. In both cases it is wise to repeat the measurement at a higher <Range>
setting, in this case the “G” setting (see Example 7).
8
Example 7: reliable measurement at high <Range> setting
The same patient as in Example 6, but measured with the “G” setting. This is a reliable
measurement (esd0.08 and Q1). The chosen range in Example 6 was apparently too low.
Additional information
More information about the working principles of the C-Quant can be found in the separate
document “Compensation Comparison in the Oculus C-Quant straylight meter”. More
information about retinal straylight in general and its relation to other measures of visual function
can be found in the separate document “Introduction to retinal straylight”. More thorough
references related to these subjects can be found in the separate document “C-Quant literature
overview”. For additional information, please contact:
Tom van den Berg
Ocular Signal Transduction group
Netherlands Institute for Neuroscience
Amsterdam, The Netherlands
Phone: +31-20-5665185
Email: t.j.vandenberg
9
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertising