Lensometry

Lensometry is a technique that measures the dioptric power of spectacle lenses.

• 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]

• 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]

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