Measurements are easier with intermediate pupil dimensions (around 5 mm). 2WIN emits infrared rays all over the eye. When pupil aperture is too small it cannot measure refraction while, on the contrary, when pupil aperture is too large, measurements may be invalidated by aberrations of the corneal periphery.

Yes. Under the same conditions measurements should remain within the device’s precision range (precision of measurement for spherical/cylindrical defect: +/- 0.25 D, precision of measurement for cylindrical axis: +/- 5 degree). Variables that influence conditions are those relating to the surrounding environment. A change in luminosity influences the aperture of the pupil. Changes in pupil size can create aberrations that alter ocular refraction.

The human optical system is another extremely important variable and is continually changing. A person may have different refraction in the morning and in the evening, including diopters of difference.

Measuring at a distance of 1m, accommodation certainly plays a part.

This will clearly be more evident in children than in adults.

2WIN has only a slight accommodation stimulus, leading to partial accommodation in children (the ‘fast’ kind that is normally not corrected with glasses). In adults it is so slight that it can be ignored.

Yes. It is better not to wait for the pupil to dilate completely in order to avoid the diameter of the pupil being excessive, leading to aberrations or preventing measurements being taken.

The device will not give a result and will only signal a level of myopia or hypermetropia that is too high. Using test lenses and over-refraction, you can obtain refraction through a difference of values.

Accommodation can be reduced by taking a second measurement in the subject, asking them to focus on a target 3-5m behind the operator. As long as the subject’s gaze is near 2win, the operator can ‘detect’ the pupil and obtain a refractive value with a non-accommodating eye.

Of course, if you make sure – in the case of glasses – to incline the lenses downwards to avoid a double reflection. There is no problem with contact lenses.

Of course, as long as pupil movement is not excessive and the subject is not clearly cross-eyed.

Depending on the degree of opacity of the crystalline lens, the device may give a degree of reliability that is higher or lower, or may not give any result at all.

No. You must take monocular measurements, focussing one eye at a time and covering the other and by endeavouring to get the patient to look towards the centre of 2WIN.

Of course  - in monocular mode.