Lensometry
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Lensometry is a technique that measures the dioptric power of spectacle lenses.
How to Perform the Test?
- Adjust the focusing eyepiece of the lensometer so that it reads 0 D on the measuring drum with the target crisply in focus.
- Place the spectacles in the lensometer with the ocular surface away from the examiner.
- Measure the right lens first. Then measure the left lens.
- Center the spectacles within the carriage of the instrument so that the target is centrally aligned within the eyepiece reticle.
- From an excess plus power direction, rotate the power drum of the lensometer so that the target comes to a sharp focus in the first meridian,
simultaneously rotating the axis drum and making its target lines contiguous. This is the first meridian. Note the position of the power drum.
- Continue rotating the power drum until the second meridian comes into sharp, contiguous focus. This is the second meridian. Note the position of the
power and axis drums.
- If both meridians come to a sharp focus simultaneously, the lens is spherical. If there are two distinctly different foci, the lens is spherocylindrical.
- If there is an add, measure it.
- The spherical or spherocylindrical power and axis is recorded in minus cylinder form.
- The multifocal add, if present, is recorded as a plus add. [1]
Useful Tips
- Focus the lensometer before each reading.
- Carefully fine-tune the power and the axis drums.
- If the lens is a multifocal lens, look carefully for the maximum plus power position of the lens. [2]
References
- ↑ Comparison of Preschool Vision Screening Tests as Administered by Licensed Eye Care Professionals in the Vision in Preschoolers Study. Am Acad Ophthalmol 2004;111(4):637-650
- ↑ Preschool Vision Screening Tests Administered by Nurse Screeners Compared with Lay Screeners in the Vision in Preschoolers Study. Invest Ophthalmol Vis Sci 2005;46(8):2639-2648
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