RED AND GREEN LENSES USED IN OPHTHALMUC PRACTICE
The standard trial lens set also contains one red and one green filter lens. Some trial lens also contains one yellow filter. These filter lenses are used to check over-correction and under-correction of refractive error.
Under ordinary condition of illumination, the eyes are emmetropic for yellow, myopic for green and hypermetropic for red.
With each eye occluded in turn, the uncovered eye views the best line first through the red filter, which is rapidly exchanged for green filter successively.
The patient is asked to make a comparison of definition through the filter to notice the clarity of letters. If the patient states:
• No apparent difference between the two, it implies optimum correction is present.
• Vision is clearer with red, the eye is slightly fogged. A small minus can be added until equality is achieved.
• Vision is clearer with green, the eye is hypermetropic and a plus lens can be added until equality is reached.
• If red and green appear clearer alternatively before any adjustment is made in the correction, this indicates accommodation is active. In such case it is better to abandon the test Red and green filters are also used for macular perception test.
If the patient can identify red and green color, macula can be taken as functioning. They are great tool for Worth 4 Dot test to ensure eye teaming or to detect diplopia.
Yellow filter is sometimes used to break the confusion of the patient to identify correct observation.
OPTOMETRY-SHARP VISION
Optometrist