Error Analysis of Corneal Thickness Measurements

Arner, Robert S.; Rockfor, d; Rengstorff, Roy H.

doi:10.1097/00006324-197210000-00008

Cited by 10 publications

(4 citation statements)

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“…Thus, the increase of CCT was mainly due to the increase in the stromal thickness. Although OCT measurement may be affected by the changes in corneal refractive index due to corneal edema after surgery, it has been suggested that potential errors of estimating the thickness induced by edema could be below 3.0% [26]. The possible error may not explain measured swelling of the cornea and DEC in the present study.…”

Section: Discussionmentioning

confidence: 63%

Phacoemulsification Induced Transient Swelling of Corneal Descemet’s Endothelium Complex Imaged with Ultra-High Resolution Optical Coherence Tomography

et al. 2013

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PurposeThickness changes of corneal sub-layers after phacoemulsification were investigated by spectral domain ultra-high resolution optical coherence tomography (UHR-OCT). MethodsThe corneas (n = 26) of 26 age-related cataract surgery patients were studied. UHR-OCT was used to evaluate the thickness of Descemet’s Endothelium Complex (DEC), stroma, Bowman’s layer, epithelium, and full cornea at the center (CCT) before, one day after, and one week after surgery. Non-contact specular microscopy measured CCT, endothelial cell density, and morphology.ResultsThe DEC, stroma, Bowman’s layer, and epithelium were visualized by UHR-OCT. Before surgery, the DEC in all cases appeared as a translucent space between two smooth opaque lines. One day after surgery, the posterior corneal surfaces in half of the eyes were wavy and irregular. Compared to the baseline, one day after surgery the thickness increases of the DEC, stroma, and CCT were 4.3 ± 2.6 µm, 25.5 ± 24.9 µm, and 32.1 ± 26.6 µm, respectively (P < 0.001). The morphology of the DEC and the CCT recovered to baseline one week after surgery (P > 0.05), but endothelial cell density was 8.7% less than at baseline. There were no significant changes in Bowman’s layer and epithelium after the operation. The pre-operative DEC thickness was positively correlated with the decreased endothelial cell density at 1 day after surgery (r = 0.55, P = 0.003).ConclusionsThe DEC showed edematous thickening and different degrees of morphological changes after phacoemulsification. The DEC deformation and corneal edema recovered by one week after surgery, which indicated recovery of endothelial function. UHR-OCT is a useful tool to evaluate function of the DEC after phacoemulsification. Pre-operative DEC thickness may indicate the integrity of the endothelium and could be used for predicting endothelial cell loss after phacoemulsification.

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Section: Discussionmentioning

confidence: 63%

Phacoemulsification Induced Transient Swelling of Corneal Descemet’s Endothelium Complex Imaged with Ultra-High Resolution Optical Coherence Tomography

et al. 2013

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“…Corrections for variation in horizontal corneal curvature have been made when appropriate, whereas no correction for variation in refractive index due to stromal swelling has been attempted. The importance of changes in refractive index in the study of corneal thickness was emphasized by Arner & Rengstorff (1972), who calculated a 3'O/o increase in apparent thickness if the corneal refractive index was reduced to that of water. Similarly, from the refractive index of dry cornea reported by Fischer (1930) (1.384) a 1 O/o decrease in apparent thickness could be accounted for.…”

Section: ' (X-x)'mentioning

confidence: 99%

Graft Thickness After Penetrating Keratoplasty

Ehlers¹

1974

Acta Ophthalmologica

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Graft thickness was studied in 70 patients subjected to Penetrating keratoplasty. A postoperative swelling was followed by a decreasing thickness during 3-4 months, after which period the graft was found to be thinner than normal, and in cases with a normal contralateral eye, thinner than the cornea of that eye. During the following months the graft thickness increased and finally assumed the value of the contralateral cornea. Any complications during the postoperative course were immediately reflected in an increased thickness. Quantitative data supporting the above statements are given, treated statistically when adequate.

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“…Since thickness is determined along the normal to the anterior surface, and a diffuse scattering of light from the posterior surface is viewed, knowledge of the radius of the posterior surface of the cornea is not necessary with this pachometer arrangement. This statement is contrary to the opinions of Maurice and Giardini (195 1) and Arner and Rengstorff (1972). The sagittal thickness, or minimum thickness (which is equivalent to the thickness along the normal to the posterior surface of the cornea) can be calculated from the measurements made with this arrangement, but the back surface radius must then be known.…”

Section: Exactmentioning

confidence: 85%

“…Errors in the estimation of refractive index are of less importance (corneal hydration would need to alter by some 7-8 YO to produce a 1 % error in the estimate oft), whilst variation in the corneal radius of curvature between individuals can virtually be ignored. Further discussion on sources of error in pachometry measurements may be found in other references (Arner and Rengstorff, 1972;Fatt and Harris, 1973;Patel, 1981;Edmund and LaCour, 1986).…”

Section: Discussionmentioning

confidence: 99%

Theoretical principles of optical pachometry

Brennan

Smith

Macdonald

1989

Ophthalmic Physiologic Optic

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Various configurations have been suggested for the optical measurement of corneal thickness by slit beam doubling, and corresponding ray traces have been provided to relate actual thickness to apparent thickness. In this report, a set of equations is provided which apply to the general situation in which neither the angle of illumination nor the angle of observation are aligned with or symmetrical about the normal to the cornea. An explicit solution to these equations giving true corneal thickness in terms of apparent thickness cannot be established, and an iterative procedure is used to develop a relationship for a number of different pachometer configurations. The near linearity of these relationships suggests the existence of a simple equation to relate these entities. By making appropriate assumptions, a linear approximation relating the inverse of the true thickness to the inverse of the apparent thickness is developed. An equation for determining the location of measurements of peripheral corneal thickness is also derived. The equations presented here may be generally applied to all optical pachometer configurations, can be used to estimate the relative contributions of various sources of error in pachometry and provide a basis for obtaining uniform absolute derivations of corneal thickness.

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Error Analysis of Corneal Thickness Measurements

Cited by 10 publications

References 0 publications

Phacoemulsification Induced Transient Swelling of Corneal Descemet’s Endothelium Complex Imaged with Ultra-High Resolution Optical Coherence Tomography

Phacoemulsification Induced Transient Swelling of Corneal Descemet’s Endothelium Complex Imaged with Ultra-High Resolution Optical Coherence Tomography

Graft Thickness After Penetrating Keratoplasty

Theoretical principles of optical pachometry

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