Combining refractive and topographic data in corneal refractive surgery for astigmatism

Næser, Kristian

doi:10.1111/j.1755-3768.2011.02211.x

Cited by 12 publications

(8 citation statements)

References 16 publications

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“…It is generally accepted that the incision causes a fla ening effect along the orienta on in which it is applied. These curvature changes result in significant altera ons to the magnitude [16][17][18] and orienta on of the principal meridians post-surgically which was similar to the finding of this study that showed fla ening of the ver cal meridian at 2 weeks and at 6 weeks.…”

Section: Methodssupporting

confidence: 87%

Astigmatic Changes in Sutureless Small Incision Cataract Surgery

Yadav

Bajracharya

Shrestha

et al. 2021

Birat J. Health Sci.

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Introduction: Cataract is the main cause of bilateral blindness in Nepal. Surgery is the accepted treatment option for cataract with Small incision Cataract Surgery (SICS) and Phacoemusification being the common procedures being performed with comparable results. Corneal astigmatism has been a byproduct of cataract surgery since the first limbal incision was made with improved techniques. Self-sealing scleral pocket incisions are stable and provides early healing, faster visual restoration and more importantly superior astigmatism control. A variety of scleral incisions are being used in manual SICS, with the aim of keeping the post-operative astigmatism to a minimum. Despite having many techniques of scleral incision, there have been only few studies which compares surgical induced astigmatism (SIA) between them Objective: To determine surgical induced astigmatism following frown, chevron and straight incision forms in suture-less small incision cataract surgery(SICS). Methodology: A prospective study was done on a total of 120 patients aged 40years and above with senile cataract. The patients were randomly divided into three groups where each group received specific incision- Straight, Frown and Chevron. SICS with intraocular lens (IOL) implantation was performed. The patients were compared on 2 weeks and 6 weeks post operatively for uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA) and keratometric reading. Surgical induced astigmatism (SIA) was calculated using the SIA calculator version 2.0. The study was analysed using SPSS version 20.0. Results: At 6 weeks UCVA of 6/18-6/6 was attained by 63.41%, 78.94% and 84.61% of patients in group straight, frown and chevron. However about 97% of patients attained BCVA of 6/18-6/6 in all three groups. Mean SIA was least in Chevron group (0.30 D ± 0.16) and was most in the straight group (1.22 D ±0.36) which was statistically significant. Conclusion: Chevron incision induces the least astigmatism compared to frown and straight incision.

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Section: Methodssupporting

confidence: 87%

Astigmatic Changes in Sutureless Small Incision Cataract Surgery

Yadav

Bajracharya

Shrestha

et al. 2021

Birat J. Health Sci.

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“…

{REF}_{normalC} = {REF}_{normalV} / false(1 - ({REF}_{normalV} * V / 1000) false),

where REF C is the corneal plane refraction, REF V the vertex plane refraction and V the vertex distance in mm. The resulting net astigmatism was transformed to polar values (Naeser ). All calculations are illustrated in Example 1 – Manifest refraction.…”

Section: Methodsmentioning

confidence: 99%

“…These transformations were carried out as described on page 769–70 of Naeser (). Manifest refraction (= spectacle correction) with a vertex distance of 15 mm: 2.0–3.75 axis 75°.…”

Section: Methodsmentioning

confidence: 99%

“…Converting to polar values, with the reference meridian Φ = the steeper anterior corneal meridian = 171°: KP(Φ) ACA = 4.63*cos(2 (171-171)) = 4.63 D; KP(Φ + 45) ACA = 4.63*sin(2(171-171)) = 0 D. Manifest refraction. These transformations were carried out as described on page 769-70 of Naeser (2012). Manifest refraction (= spectacle correction) with a vertex distance of 15 mm: 2.0-3.75 axis 75°.…”

Section: Net Curvital Power ¼ Kpðuþmentioning

confidence: 99%

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Refractive, anterior corneal and internal astigmatism in the pseudophakic eye

Bregnhøj

Mataji

Næser

2014

Acta Ophthalmologica

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ABSTRACT.Purpose: To evaluate the correlation between refractive astigmatism (RA) and anterior corneal astigmatism (ACA), and determine the internal astigmatism (IA) in 184 pseudophakic eyes. Methods: The study was a prospective non-masked single-centre study. Patients were examined 8 weeks after phacoemulsification with implantation of aspheric one-piece monofocal IOLs. Examination included autokeratometry and subjective refraction. All refractive data were converted to the corneal plane. The corneal refractive index, taken to be 1.376, was used to estimate the ACA. All astigmatisms were converted to net curvital and net torsional powers with the steeper corneal plane as the reference meridian. Curvital power is the force acting along a given meridian, and torsion is the power twisting the astigmatic direction out of that plane. The internal astigmatism (IA) was calculated as the difference between RA and ACA. Results: For curvital powers, the refractive astigmatism (KP(Φ) RA ) could be described as a function of anterior corneal astigmatic magnitude (KP(Φ) ACA ) and direction a by the multiple linear regression equation: KP (Φ) RA = À0.09 + 0.61*KP(Φ) ACA + 0.33*cos2a, (r 2 = 0.59, p < 0.0001). The average internal astigmatism amounted to 0.47 D inclined 92°relative to the steeper anterior corneal meridian. The magnitude of internal astigmatism depended on the angle a of the steeper anterior corneal meridian, averaging 0.86 D at 91°for with-the-rule, 0.37 D at 95°for oblique and 0.17 D at 97°for against-the-rule corneal astigmatisms. Conclusions: The internal astigmatism varies as a function of the direction of the anterior steeper corneal meridian. In patient candidates to surgical correction of astigmatism, measuring only the curvature of the anterior corneal surface and neglecting that of the posterior corneal surface can lead to inaccurate evaluation of total corneal astigmatism.

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“…In the first, we simply used the magnitude for evaluation. In the second method, we used a vector-based approach outlined by Naeser et al [7], where the astigmatism values were divided into two polar values. The first, KP(45), along the 45-degree meridian, and the second, KP(0), along the zero degrees meridian.…”

Section: Corneal Astigmatismmentioning

confidence: 99%

The Influence of Tomographic Corneal Characteristics on Epithelial Thickness Profile

Hashmani

Hashmani²,

Hashmani

et al. 2020

Cureus

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To understand the influence of tomographic corneal characteristics on the epithelium of normal eyes. Methods We scanned a total of 98 eyes of 98 individuals using anterior segment tomography and a spectral-domain optical coherence tomography (OCT) epithelial mapping tool. Only eyes with no previous pathology were included, with a refractive range of +5 diopters (D) to-6 D, intraocular pressure of < 22 mmHg, and no evidence of dry eye (Schirmer's test 2 value > 5 mm). Corneal curvature metrics were statistically correlated with regional epithelial thickness parameters. Results The anterior and posterior corneal surface flat and steep axis, the maximum and minimum curvature, corneal topographic astigmatism, astigmatism polar values, and corneal volume had no statistically significant correlation (p>0.05) with the epithelial thickness. Similarly, anterior corneal surface asphericity had no significant correlation. Posterior surface asphericity had a statistically significant moderate correlation with the epithelium in all areas. Similar results were seen in the multivariate analysis. Conclusions None of the front or back surface parameters had any influence on the corneal epithelium except for the posterior surface asphericity. This statistically significant yet clinically insignificant correlation may be enhanced in diseased populations like keratoconus and could indicate epithelial remodeling with early posterior corneal changes.

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Combining refractive and topographic data in corneal refractive surgery for astigmatism

Cited by 12 publications

References 16 publications

Astigmatic Changes in Sutureless Small Incision Cataract Surgery

Astigmatic Changes in Sutureless Small Incision Cataract Surgery

Refractive, anterior corneal and internal astigmatism in the pseudophakic eye

The Influence of Tomographic Corneal Characteristics on Epithelial Thickness Profile

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