Biomedical subjects

M Dam-Johansen

Publications and source records attributed to M Dam-Johansen.

4 recordsLinked to original sources

PubMed1996

Evaluating surgically induced astigmatism by Fourier analysis of corneal topography data.

PURPOSE: To evaluate surgically induced astigmatism using Fourier harmonic series analysis of corneal topography data. SETTING: Aarhus Kommunehospital, Aarhus University, Denmark. METHODS: We evaluated the results of 46 phacoemulsifications with a 4 or 6 mm scleral tunnel sutureless incision based on the axis of the steepest meridian. We performed conventional keratometry and corneal topography before and up to 1 month after surgery. Using Fourier analysis, the corneal topographic images were broken into spherical power, regular astigmatism, and nonregular astigmatism for individual or aggregate analysis of surgically induced astigmatism. The induced refractive change (average of the difference between preoperative and postoperative corneal topographies) was analyzed and normalized according to the surgical meridian and to right/left eye. RESULTS: Regular astigmatism calculated by Fourier analysis of mires from the keratometer zone correlated well with conventional keratometry readings. Surgery induced a localized flattening in the superior region and a with-the-rule regular astigmatism component in the central area. CONCLUSION: Surgically induced corneal topography changes can be analyzed by Fourier series harmonic analysis, allowing aggregate data to be broken into optically meaningful quantities.

Adult↗

PubMed1994

Evaluating surgically induced astigmatism.

Using a modification of vector analysis for calculating surgically induced astigmatism, we describe a simple method that divides the induced cylinder into two orthogonal components. This decomposition allows with-the-rule and against-the-rule astigmatic changes to be calculated for individual case analysis, as well as for statistical analysis of aggregate data. Because it is based on the true induced cylinder, as determined by optical principles, this method overcomes some of the problems associated with earlier methods of evaluating surgically induced astigmatism.

Astigmatism↗

PubMed1993

[Cataract surgery using phacoemulsification].

Clinical results are reported in a consecutive series of 111 patients undergoing cataract surgery by phacoemulsification. On the first day after surgery, 69% of all cases had a visual acuity of 20/40 or better without any spectacle correction. Four months later this percentage had increased to 79%. Compared with a series of patients, operated by conventional extracapsular extraction, the corneal astigmatism was found to be significantly reduced in the phacoemulsification series (p < 0.001). The decrease in surgically induced astigmatism together with tailoring of the power of the intraocular lens (IOL) accounted for the good unaided visual acuity in the phacoemulsification group. Phacoemulsification is concluded to offer good optical control of the postoperative refraction in cataract patients.

Adult↗

PubMed1993

Refractive results after phacoemulsification and ECCE. A comparative study.

The refractive results were evaluated in 79 patients undergoing cataract extraction by phacoemulsification using a 6-7 mm tunnel incision, and compared with a group of 77 patients undergoing planned extracapsular cataract extraction (ECCE) by the same surgeon. A mean increase in the keratometric cylinder of 0.05D and 0.52D was found in the phacoemulsification and the extracapsular cataract extraction group, respectively. This was significantly different from zero for the extracapsular cataract extraction group (p < 0.05) but not for the phacoemulsification group (p > 0.05). By vector analysis, the mean surgically induced astigmatism was 0.91D and 1.36D in the phacoemulsification and the extracapsular cataract extraction group, respectively (p < 0.01). The IOL power prediction error (spectacle plane) was found to be 0.17D (+/- 0.69 SD) in the phacoemulsification group and 0.02 D (+/- 0.79 SD) in the extracapsular cataract extraction group, respectively. We conclude that phacoemulsification improves the surgical control of the refractive outcome of cataract surgery.

Aged↗