| Abstract |
Purpose
Automated refractokeratometry forms a basic exam at the start of the opthalmic
routine for the evaluation of sphero-cylindrical refractive error.
HRK-7000 is a new generation auto-refractokeratometer based on Shack –
Hartmann principle.
The aim of this thesis was to evaluate its repeatability and accuracy in
refractometry and keratometry measurements in the presence and absence
of cycloplegia.
Methodology
Forty-five healthy myopes ,with a mean age 28,6 years (S.D: 6.5 years ) and
mean spherical equivalent, R.E: -5,22 D (S.D : 2.14 D) participated in the
present study .
Initially the examinations included refractometry and keratometry
measurements with HRK-7000.The measurements in keratometry included
central and peripheral measurements. The central zone was defined at 3mm
and the peripheral zone at 6mm.Four points were measured for the
peripheral zone: (nasal,temporal, superior, inferior)
In each case two individual measurements were taken , within a short time
interval for the estimation of repeatability.
Accuracy in refractometry was evaluated by comparing HRK-7000 with
subjective manifest refraction measurements and accuracy in keratometry
was evaluated by comparing HRK-7000 with C-Scan corneal topographer
measurements. Subsequently , the individuals were subjected to cycloplegia
.After 30 minutes the examinations of refractometry and keratometry with
HRK-7000 were repeated to evaluate the impact of cycloplegia.
Results
Refractive error analysis was performed using Fourier decomposition and each
prescription was devided in three parts : MSE(mean spherical equivalent) ,
J0 (astigmatism at 180º or 90º)and J45 (oblique astigmatism at 45º or 135º)
Repeatability analysis for the refractometry measurements showed no statistical
significant difference between the two measurements.
Accuracy for the refractometry measurements showed statistical differences in
both conditions (no cycloplegia , under cycloplegia ) .More specifically the
measurements with HRK-7000 are found to be more hyperopic than
manifest refraction measurements for the spherical equivalent by 0,13 ±
0,33 D in the measurements without cycloplegia and by 0,26 ± 0,25 D in the
measurements under cycloplegia. Although the mean difference is bigger in
the measurements with cycloplegia ,the two methods seem to correlate
better in the presence of cycloplegia (narrower limits of agreement).
Instillation of cyclopental 1% caused a hyperopic shift of refractive error for
the spherical equivalent by 0,33 ± 0,31 D .This shift is clinically significant
and was also found statistically significant.
Repeatability analysis for the keratometry measurements showed no statistical
significant difference .
Accuracy analysis for the keratometry measurements showed statistical
differences for all comparisons and clinical differences for K Nasal (0,23 ±
0,47 mm) and K Superior ( 0,16 ± 0,23 mm)
Conclusions
HRK-7000 showed very high repeatability and accuracy in the refractometry
measurements. Its repeatability and accuracy are within the limits of
agreement found in similar studies.
The instillation of cyclopental 1% causes a hyperopic shift of refractive error as
expected.
HRK-7000 showed good repeatability centrally in the keratometry
measurements , which degraded in the periphery .The accuracy of
HRK-7000 for the keratometric measurements was also good centrally but
degraded in the periphery.
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Μελέτη της εγκυρότητας αυτόματου διαθλασίμετρου πριν και μετά τη χρήση κυκλοπληγικού φαρμάκου
