### Abstract

PURPOSE: To determine the new corneal effective index of refraction (rN) following LASIK to be used for accurate keratometry reading (K-reading). METHODS: A total of 332 eyes that underwent myopic LASIK were divided into two groups (group A [n=137] and group B [n=195]). In each group, patients were divided into four subgroups according to the amount of spherical equivalent refraction of myopic LASIK ablation (subgroup 1 [-12.0 D]). In each subgroup of group A, K-reading was measured by the clinical history method and the new corneal effective index (rN) was determined using paraxial formula: (K-reading=(rN-1)/Ra), where Ra is the radius of curvature of the anterior corneal surface. In group B, the anterior radius of curvature of the cornea was determined by automated K-reading, and K-reading was measured in each subgroup using the new effective index in paraxial formula, clinical history method, and automated K-reading. RESULTS: In group A, the new effective index of refraction was 1.3355, 1.3286, 1.3237, and 1.3172 in the four subgroups, respectively. In group B, the mean K-reading measurements using rN in paraxial formula, clinical history method, and automated K-reading were: 40.33±1.68 D, 40.33±1.67 D, and 40.54±1.69 D, respectively, in subgroup 1; 37.96±1.26 D, 38.03±1.38 D, and 38.98±1.28 D, respectively, in subgroup 2; 35.77±1.75 D, 35.84±1.85 D, and 37.29±1.83 D, respectively, in subgroup 3; and 34.03±1.49 D, 34.15±1.84 D, and 36.21±1.59 D, respectively, in subgroup 4. In all subgroups of group B, the results of K-reading obtained using the new effective index of refraction were statistically similar to the results obtained by clinical history method (P>.05). Automated K-reading statistically overestimated the K-reading values in subgroups 2, 3, and 4 of group B (P

Original language | English (US) |
---|---|

Pages (from-to) | 75-80 |

Number of pages | 6 |

Journal | Journal of Refractive Surgery |

Volume | 22 |

Issue number | 1 |

State | Published - Jan 2006 |

Externally published | Yes |

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### ASJC Scopus subject areas

- Ophthalmology

### Cite this

*Journal of Refractive Surgery*,

*22*(1), 75-80.

**Intraocular lens power calculation following LASIK : Determination of the new effective index of refraction.** / Jarade, Elias F.; Abi Nader, Françoise C.; Tabbara, Khalid F.

Research output: Contribution to journal › Article

*Journal of Refractive Surgery*, vol. 22, no. 1, pp. 75-80.

}

TY - JOUR

T1 - Intraocular lens power calculation following LASIK

T2 - Determination of the new effective index of refraction

AU - Jarade, Elias F.

AU - Abi Nader, Françoise C.

AU - Tabbara, Khalid F.

PY - 2006/1

Y1 - 2006/1

N2 - PURPOSE: To determine the new corneal effective index of refraction (rN) following LASIK to be used for accurate keratometry reading (K-reading). METHODS: A total of 332 eyes that underwent myopic LASIK were divided into two groups (group A [n=137] and group B [n=195]). In each group, patients were divided into four subgroups according to the amount of spherical equivalent refraction of myopic LASIK ablation (subgroup 1 [-12.0 D]). In each subgroup of group A, K-reading was measured by the clinical history method and the new corneal effective index (rN) was determined using paraxial formula: (K-reading=(rN-1)/Ra), where Ra is the radius of curvature of the anterior corneal surface. In group B, the anterior radius of curvature of the cornea was determined by automated K-reading, and K-reading was measured in each subgroup using the new effective index in paraxial formula, clinical history method, and automated K-reading. RESULTS: In group A, the new effective index of refraction was 1.3355, 1.3286, 1.3237, and 1.3172 in the four subgroups, respectively. In group B, the mean K-reading measurements using rN in paraxial formula, clinical history method, and automated K-reading were: 40.33±1.68 D, 40.33±1.67 D, and 40.54±1.69 D, respectively, in subgroup 1; 37.96±1.26 D, 38.03±1.38 D, and 38.98±1.28 D, respectively, in subgroup 2; 35.77±1.75 D, 35.84±1.85 D, and 37.29±1.83 D, respectively, in subgroup 3; and 34.03±1.49 D, 34.15±1.84 D, and 36.21±1.59 D, respectively, in subgroup 4. In all subgroups of group B, the results of K-reading obtained using the new effective index of refraction were statistically similar to the results obtained by clinical history method (P>.05). Automated K-reading statistically overestimated the K-reading values in subgroups 2, 3, and 4 of group B (P

AB - PURPOSE: To determine the new corneal effective index of refraction (rN) following LASIK to be used for accurate keratometry reading (K-reading). METHODS: A total of 332 eyes that underwent myopic LASIK were divided into two groups (group A [n=137] and group B [n=195]). In each group, patients were divided into four subgroups according to the amount of spherical equivalent refraction of myopic LASIK ablation (subgroup 1 [-12.0 D]). In each subgroup of group A, K-reading was measured by the clinical history method and the new corneal effective index (rN) was determined using paraxial formula: (K-reading=(rN-1)/Ra), where Ra is the radius of curvature of the anterior corneal surface. In group B, the anterior radius of curvature of the cornea was determined by automated K-reading, and K-reading was measured in each subgroup using the new effective index in paraxial formula, clinical history method, and automated K-reading. RESULTS: In group A, the new effective index of refraction was 1.3355, 1.3286, 1.3237, and 1.3172 in the four subgroups, respectively. In group B, the mean K-reading measurements using rN in paraxial formula, clinical history method, and automated K-reading were: 40.33±1.68 D, 40.33±1.67 D, and 40.54±1.69 D, respectively, in subgroup 1; 37.96±1.26 D, 38.03±1.38 D, and 38.98±1.28 D, respectively, in subgroup 2; 35.77±1.75 D, 35.84±1.85 D, and 37.29±1.83 D, respectively, in subgroup 3; and 34.03±1.49 D, 34.15±1.84 D, and 36.21±1.59 D, respectively, in subgroup 4. In all subgroups of group B, the results of K-reading obtained using the new effective index of refraction were statistically similar to the results obtained by clinical history method (P>.05). Automated K-reading statistically overestimated the K-reading values in subgroups 2, 3, and 4 of group B (P

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M3 - Article

VL - 22

SP - 75

EP - 80

JO - Journal of Refractive Surgery

JF - Journal of Refractive Surgery

SN - 1081-597X

IS - 1

ER -