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Biomedical subjects

Kristian Naeser

Publications and source records attributed to Kristian Naeser.

9 recordsLinked to original sources
PubMed2006

The power of a cylinder in an oblique meridian: revisiting an old controversy.

The sine-squared correlation states that the cylinder power in an oblique meridian forming an angle beta with the axis of the cylinder is reduced to sin(2)beta of the maximal power. The sine-squared relationship is fundamental in paraxial optics, but its validity has repeatedly been questioned during the last century. It appears that two powers are operative in an oblique meridian, curvital and torsional. Curvital power is responsible for refraction in the plane of the meridian, while the torsional component twists the light out of that plane. Curvital power is the traditional power concept, while torsional power has only recently been described. The long-standing criticism of the sine-squared correlation is based on the erroneous assumption that only curvital power is operational in paraxial imagery. Curvital and torsional power are both derived from the sine-squared correlation. The concept of these dual powers repudiates the criticism and is in complete accordance with paraxial optics.

Astigmatism↗
PubMedDate not supplied

Bivariate polar value analysis of surgically induced astigmatism.

PURPOSE: To demonstrate the use of bivariate polar value analysis of surgically induced astigmatism following various cataract incisions. METHODS: In a prospective study, we investigated surgically induced astigmatism following cataract surgery through 9.0-mm, 5.5-mm, and 4.0-mm superior corneal incisions. Autokeratometry was performed preoperatively and during the first year. All net astigmatisms were converted to polar values with reference to the 90 degrees meridian. Univariate and bivariate polar value analyses were performed. RESULTS: After 1 year, univariate polar value analysis disclosed flattening averaging 1.02 D for 9.0-mm incisions, 0.71 D for 5.5-mm incisions, and 0.64 D for 4.0-mm incisions. The induced torque was 0.46 D counterclockwise for the 9-mm incision and close to zero for the 5.5 and 4-mm incisions. Bivariate polar value analysis disclosed a statistically significant (P < .05) difference in surgically induced astigmatism between the 9.0-mm incisions and the two smaller incisions at all follow-up points. CONCLUSION: Univariate polar value analysis demonstrated the surgically induced steepening and torque. Bivariate analysis demonstrated the joint variation in these entities and therefore always yielded the correct result. Univariate and bivariate polar values may be used for analysis of surgically induced astigmatism following cataract surgery in any meridian.

Adult↗