Effect of instrument rotation on handheld keratometry

Lam, Andrew; Chan, Rufina; Chiu, Roger

doi:10.1016/j.jcrs.2004.04.069

Cited by 9 publications

(7 citation statements)

References 13 publications

(5 reference statements)

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“…However, few studies have assessed the comparability of corneal astigmatism and axis location, both of which play an important role in the surgical correction of cylindrical errors. [27][28][29] Moreover, to our knowledge, ours is the first study to compare these astigmatic parameters between autokeratometry and corneal topography, both of which are quick and convenient methods for measuring these variables in a clinical setting. Table 4 shows a summary of previous studies of agreements in corneal astigmatism, axis location, and astigmatic vector components measurements between keratometry and corneal topography.…”

Section: Discussionmentioning

confidence: 99%

“…They found that the 2 devices showed poor agreement between measurements of corneal astigmatism and axis location, possibly as a result of an irregular corneal surface. Lam et al 29 compared J0, J45, and axis location between a handheld autokeratometer and a corneal topographer. The handheld keratometer was in agreement with the topographic keratometer; however, the differences between the 2 devices increased with the rotational effect.…”

Section: Discussionmentioning

confidence: 99%

“…The 95% LoA between the 2 devices in corneal astigmatism, axis location, and astigmatic vector components in the present study were smaller than those in previous studies. [27][28][29] Moreover, our sample size exceeded the minimum and was far larger than in previous studies. In our study, all 57 eyes were within G0.50 D of the differences in astigmatic vector components between the 2 devices, suggesting that the ARK-700A autokeratometer and the Atlas corneal topographer can be used interchangeably for measuring these parameters in a clinical setting.…”

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

Comparison of corneal power, corneal astigmatism, and axis location in normal eyes obtained from an autokeratometer and a corneal topographer

Kobashi¹,

Kamiya²,

Igarashi³

et al. 2012

Journal of Cataract and Refractive Surgery

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Comparison of corneal power, corneal astigmatism, and axis location in normal eyes obtained from an autokeratometer and a corneal topographer

Kobashi¹,

Kamiya²,

Igarashi³

et al. 2012

Journal of Cataract and Refractive Surgery

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“…When the power vector method was applied, the changes were still small and within onesixth of a dioptre. The vector representation is more sensitive in revealing corneal power changes 31,32 however, the order of change is too small to be considered as clinically significant.…”

Section: Discussionmentioning

confidence: 99%

The effect of mydriasis from phenylephrine on corneal shape

Huang

Lam

2007

Clinical and Experimental Optometry

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Purpose: A previous study reported that pharmacologically-dilated pupils changed the corneal shape. Researchers used mydriatic agents with significant cycloplegic effect. The current study investigates the effect of mydriasis on corneal shape using phenylephrine alone, where phenylephrine has minimal effect on the accommodative system and whether corneal topography can be done after pupil dilation. Methods: Forty-four young healthy subjects with one eye randomly selected for mydriasis were used in this study. Twenty-two received one drop of 2.5% phenylephrine (group 1); the other 22 subjects had one drop of 0.4% benoxinate instilled prior to the application of 2.5% phenylephrine (group 2). They were matched for age and refractive error. Anterior chamber depth, pupil size and corneal parameters were compared before and after mydriasis. The corneal parameters included best-fit sphere (BFS), surface asymmetry index (SAI), surface regularity index (SRI) and the axial and tangential powers in the form of flattest and steepest powers, and in the form of M, J 0 , and J 45 vector presentation. Results: Group 1 and group 2 subjects had similar pre-mydriatic baseline ocular parameters. The mean (± SD) pupil dilation was 1.24 ± 0.59 mm for group 1 and 1.80 ± 0.95 mm for group 2. The dilation was significantly larger in group 2 (unpaired t-tests: t = 2.36, p = 0.02). There were no significant changes in corneal parameters from mydriasis in either group. Conclusions: Previous investigations used mydriatic agents, which affected not only the pupil size but also accommodation. The current study found that mydriasis from phenylephrine, with minimal effect on accommodation, did not result in significant corneal alteration, and corneal topography can be measured after pupil dilation with phenylephrine.

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“…With hand-held keratometry, incorrect orientation of the instrument and the patient causes inaccuracy in the measurement. 66 Therefore, it is essential with any measurement of corneal power that a vertical head and instrument orientation is achieved and maintained. The most common method in the literature for establishing the correct keratometric power and axis is automated keratometry with the IOLMaster (Carl Zeiss, California, Germany) and confirmation of this result with a computerised topographer, although which is chosen when they are disparate is not obvious.…”

Section: Aligning the Toric Iolmentioning

confidence: 99%

Surgical correction of astigmatism during cataract surgery

Buckhurst

Wolffsohn

Davies

et al. 2010

Clinical and Experimental Optometry

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High levels of corneal astigmatism are prevalent in a significant proportion of the population. During cataract surgery pre-existing astigmatism can be corrected using single or paired incisions on the steep axis of the cornea, using relaxing incisions or with the use of a toric intraocular lens. This review provides an overview of the conventional methods of astigmatic correction during cataract surgery and in particular, discusses the various types of toric lenses presently available and the techniques used in determining the correct axis for the placement of such lenses. Furthermore, the potential causes of rotation in toric lenses are identified, along with techniques for assessing and quantifying the amount of rotation and subsequent management options for addressing postoperative rotation. Correcting corneal astigmatism during cataract surgery can increase spectacle independence. For the patient, this has economic benefits 4 as well as desirable cosmetic and practical advantages. Spectacle correction of astigmatism creates meridional magnification, which when coupled with the associated back vertex distance produces retinal images that are asymmetrically magnified and distorted. Such images have been reported to reduce spatial perception 5 and adaptation to them is particularly challenging for elderly individuals, 6 in whom cataracts are more prevalent. Contrary to this, if corneal astigmatism is corrected at the corneal or intraocular lens (IOL) plane, then no significant meridional magnification is induced due to a negligible vertex distance. 7The effect of clear corneal incisions (CCIs) on surgically-induced astigmatism has been extensively examined. If placed along the steep corneal axis, the clear corneal incisions flatten the cornea, reducing the residual astigmatism. The larger the clear corneal incision, the greater the flattening effect. 8 Studies have shown that the average surgically induced astigmatism using a 3.0 to 3.2 mm clear corneal incision is~0.50 D.9,10 The temporal cornea allows easy access for incisions and is the preferred site of most surgeons, 11 however, incisions performed on the steepest axis result in superior postoperative uncorrected vision.12 Opposite clear corneal incisions require a second clear corneal incision to be placed along the steep axis of the cornea on the opposing side of the pupil. This has a larger effect than a single clear corneal incision and can correct more than one dioptre of corneal astigmatism.13,14 Limbal relaxing incisions, otherwise known as peripheral corneal relaxing incisions, can also be used to correct astigmatism C L I N I C A L A N D E X P E R I M E N T A LOPTOMETRY

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Effect of instrument rotation on handheld keratometry

Cited by 9 publications

References 13 publications

Comparison of corneal power, corneal astigmatism, and axis location in normal eyes obtained from an autokeratometer and a corneal topographer

Comparison of corneal power, corneal astigmatism, and axis location in normal eyes obtained from an autokeratometer and a corneal topographer

The effect of mydriasis from phenylephrine on corneal shape

Surgical correction of astigmatism during cataract surgery

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