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Silmo 2011: !Pide tu Checktest!
| The CheckTest is a simple, easy to use tool. It allows you to screen for additions that are too strong. This is often the cause of non-adaptation to progressive lenses. |  |
1. EYE/HAND LATERALISATION TEST
2. RED/GREEN (DUCHROME) TEST
3. HELMHOLTZ TARGET TEST
1. EYE/HAND LATERALISATION TEST
This simple and quick test allows you to determine the sensory/motive relation which exists between the eye and the hand of a subject.
There are three forms of eye/hand co-ordination:
- lateralised: right eye-right hand or left eye-left hand;
- crossed: right eye-left hand or left eye-right hand;
- indeterminate: the subject has no preference.
It is very important to know the existence of this reflex co-ordination between the hand and the sighting eye:
- for ophthalmologists, to determine the refraction accurately
- for opticians, to centre the lenses accurately
- in contact lens practice, in refractive surgery and in orthoptics.
In all cases, this preference should be determined so that the subject's visual habits remain undisturbed.
Directions for use:
 | 1. The subject has to be standing without anything in the hand. The observer holds out the CheckTest to the subject in order to observe which hand is used to take it. | | 2. The observer stands in front of the subject, and asks him/her to look at a bright source or any other small object in the distance. The observer asks the subject to position this source in the middle of the hole of the CheckTest, the subject keeping both eyes open. |  |  | 3. When the observer covers each eye with a second CheckTest or any other occluder, which eye is viewing the source can be determined. |
By this means, we can determine the cortical preference between the eye and the hand of each subject. This analysis offers you a better understanding of adaptation difficulties which some people feel with their new correction.
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2. THE RED/GREEN TEST OR DUOCHROME TEST
The Duochrome test can be used to verify the near addition. It is based on the chromatic aberration of the eye.
Without accommodation, a presbyopic, emmetropic eye which is perfectly corrected for near vision, will see the letters blacker on a green background, or with the same contrast on either background. If it is over corrected, the letters are seen blacker on the red background.
Directions for use :
The verification should be made in binocular vision. The subject's far vision correction should be in situ in the trial frame, with the spherical addition estimated for near work also in place. The test should be undertaken at the usual working distance.
 | If the near vision correction is too strong, the subject will spontaneously see the letters with greater contrast and blacker on the red background. |  | If the letters are seen clearer on the green background, it means that the near correction is too weak. |
Note: You must be careful with the interpretation of the red/green test for elderly people, because the chromatic aberration may change with age and in certain pathological conditions.
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3. HELMHOLTZ TARGET TEST
With this focusing test, you can check, or evaluate, the value of the spherical addition required by a subject according to the normal working distance.
Directions for use:
As before, verification is usually made in binocular vision, but it is also possible to perform this test monocularly.
With the near vision correction in the trial frame, the subject should hold the test at the usual working distance, and to look at the centre of the target.
If the circles at the centre of the target are seen distorted, it indicates that either the far vision correction or the spherical addition for near are not in the proper relation.
 | | Image of the distortion of
the centre of the target |
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