The NVU provides a complete subjective means of investigating the Near Vision refraction The general appearance of the unit can be seen in the illustration. It is in the form of a three side drum which is LED illuminated, and can be held by the patient or suspended by means of a special attachment from the rod of a Refactor Head. The unit should be used in a room moderately lit, or with external illumination from an ordinary reading lamp.
Side One – The Vocational Acuity Chart
The reading matter of this test is in 4 sizes of Times Roman type face, the smallest being 5 pt. When read aloud by the patient it gives them useful information as to their standard of reading vision and what it corresponds to in every day printed matter.
Side Two – The Binocular Bichromatic Chart
In addition to red and green filters this chart is fitted with Polarised screens. Used without a polarising visor this chart immediately reveals accommodation insufficiency and the chromatic balancing allows the correction of presbyopia for any working distance. Used with the visor it is possible to check one eye against the other, then balancing the accommodation for right and left.
Side Three – The Oblique Tangent Scale
The scale shows 14 degrees of Exophoria and 7 degrees of Esophoria in red colour. It provides in conjuction with the green Maddox Twirl a rapid measurment of horizontal and vertical muscle imbalances.
The Clinical Acuity Chart
This consists of a matched pair of Landolt rings graduated in size. Accurate measurement of near astigmatism can be made with cross Cylinders.
The Near Prism indicator
The targets, which consist of two dots placed horizontally and two arrows placed vertically about a central fixation cross, are polarised as well as being fitted with a red and green fixers. They can therefore be separated for right to left eyes either with a polarizing visor, red/green goggles or hand frame