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KMID : 1011420100150030219
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Journal of Korean Ophthalmic Optics Society
2010 Volume.15 No. 3 p.219 ~ p.225
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Predicting Powers of Spherical Rigid Gas-permeable Lenses Prescription
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Yu Dong-Sik
Yoo Jong-Sook
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Abstract
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Purpose: Usefulness in predicting the power of spherical rigid gas-pearmeable (RGP) lenses prescription using dioptric power matrices and arithmetic calculations was evaluated in this study.
Methods: Noncycloplegic refractive errors and over-refractions were performed on 110 eyes of 55 subjects (36 males and 19 females, aged 24.60?1.55 years) in twenties objectively with an auto-refractometer (with keratometer) and subjectively. Tear lenses were calculated from keratometric readings and base curves of RGP lenses, and the power of RGP lenses were computed by a dioptric power matrix and an arithmetic calculation from the manifest refraction and the tear lens, and were compared with those by over-refractions in terms of spherical (Sph), spherical quivalent (SE) and astigmatic power.
Results: The mean difference (MD) and 95% limits of agreement (LOA=MD?1.96SD) were better for SE (0.26D, 0.26?0.70D) than for Sph (0.61D, 0.61?0.86D). The mean difference and agreement of the cylindrical power between matrix and arithmetic calculation (-0.13D, -0.13?0.53D) were better than between the others (-0.24D, -0.24?0.84D between matrix and over-refraction; -0.12D, -0.12?1.00D between arithmetic calculation and over-refraction). The fitness of spherical RGP lenses were 54.5% for matrix, 66.4% for arithmetic calculation and 91.8% for over-refraction. Arithmetic calculation was close to the over-refraction.
Conclusions: In predicting indications and powers of spherical RGP lens fitting, although there are the differences of axis between total (spectacle) astigmatism and corneal astigmatism, Spherical equivalent using an arithmetic calculation provides a more useful application than using a dioptric power matrix.
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KEYWORD
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Rigid gas-permeable Lens, Diopric power matrix, Arithmetic calculation, Over-refraction, Astigmatism
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