CALIBRATION
The instrument has a mark that indicates the distance of the visual target from the eye. This is based on average distances recorded from a large number of Indian patients. It is recommended that the instrument be calibrated for individual subjects as follows:

1. The tapered end of the instrument (The subject end) is placed horizontally touching the central part of the inferior orbital margin so that the visual target is directly in front of the eye being tested. Push the slide rule all the way up till the end of the track and the cardholder cannot move closer to the eye.
2. Measure the distance from the center of the closed eyelid to the center of the cardholder using the calibration scale provided.
3. Move the movable reference mark to the distance measured as follows and fix it by tightening the screw.
4. Once the calibration is completed for one eye, it is not necessary to repeat this for the fellow eye unless the examiner notes gross asymmetry in facial features or in the globe prominence.

TRAINING:

1. The subject is made to sit comfortably on a chair with the full distance correction in place. It is recommended that this correction be placed on a standard trial frame. For monocular readings the fellow eye is occluded.
2. The examiner may stand or sit in front of the subject holding the instrument in the non-dominant hand in such a way that the tapered end of the instrument (The subject end) is placed horizontal, touching the central part inferior orbital margin so that the visual target is directly in front of the eye being tested.
3. Training is done using the larger optotypes (J16 or J5) cards. Place the card in the cardholder provided such that the optotypes face the subject. The sliding rule holding the card is withdrawn away from the eye almost towards the end of the track and then brought closer. The subject is instructed to report the point when he or she feels that the letters on the card begin to blur. It is recommended that the subject observe one of the letters in the card and not all the letters as a whole. This is repeated a few times until the examiner is satisfied that the subject is giving reasonable consistent and dependable response. It is important to exaggerate the movement to demonstrate to the patient what complete blur is and how to respond at the point of initial blurring of the letters.
4. The training is done repeated using convex and concave lenses in those with poor and good accommodation respectively. The “net” AA is calculated by subtracting the Diopteric value of the “additional” lens from the Diopteric reading read off the scale. However, the AA value accommodation using the larger optotypes is only a provisional value. The final value is recorded using the J2 optotypes card.

MEASUREMENT
The procedure for taking measurements with the J2 optotypes card is same as that described above in the TRAINING PROCEDURE. It is important to use the following guidelines when taking the measurements:

• The provisional value obtained during the training is always higher than the final value since larger optotypes are used in the former.
• The speed of movement during recording of the final value is kept constant. The movements are fine and confirmed by back and forth movements near the reported point of blur.
• The readings obtained by different additional lenses should closely match.
• The final reading is the statistical mean of the most consistent reading obtained.

[If, for some reason, the subject is unable to identify the J2 optotypes clearly, then the readings recorded with the larger optotypes may be taken as the final reading. In such cases the optotypes used should be indicated within Parenthesis, e.g. AA = 3.6 D (J5). This will indicate that the value reported could be an overestimation of the AA when compared to the recommended standard of J2.]

BINOCULAR MEASUREMENTS
For binocular measurements it is recommended that the subject end of the K-ranger be placed centrally, just below the nose. It is also possible to place the instrument at eye level overriding the nose using a bridging accessory (not yet provided). Binocular readings are usually better than monocular readings. However, in conditions affecting convergence, occurrence of diplopia may cause the patient to report “blur” earlier.