Tomey TMS-5 - Page 109

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and CL warpage. When the SAI value is large, glasses
may not be sufciently effective for correction.
● SRI (Surface Regularity Index)
The SRI is related to the eyesight. This is a
measurement of the local fluctuation of the refractive
power at the corneal center and inuences the potential
eyesight. When the SRI value is large, the corneal
surface within the pupil diameter shows an irregular
shape and the maximum value of the eyesight with
refractive power corrected by glasses becomes small.
The SRI value is large in the case of a dry eye, eyes
with contact lenses, external injuries, and penetrating
keratoplasty.
● PVA (Potential Visual Acuity)
Irregularity of corneal shape within the pupil diameter
affects eyesight. This irregularity is evaluated by
calculating the SRI index.
The PVA represents the best eyesight functionally
expected from the normal eye after being corrected by
glasses, according to the analysis result of the corneal
shape.
In a clinical evaluation it needs to be carefully
considered that breakage of the tear lm largely affects
the PVA (and SRI).
Prolonged gazing at a fixation target by a patient
without blinking can produce tearfilm breakup,
transiently reduced vision and abnormal Unless of PVA
or SRI.
If the PVA value is abnormal even though the patient
blinks appropriately, there may be a true irregular
corneal astigmatism including dry keratoconjunctivitis,
CL warpage, epikeratoplasty, and corneal inammation
due to herpes virus.
● CVP (Coefcient of Variation of Corneal Power)
The CVP is calculated by the SDP (standard deviation
of refractive power) based on the average of all