Developments in diagnostic tools for corneal ectasia

Gosavi, Vrushali V.; Hardten, David R.

doi:10.1586/eop.10.40

Cited by 4 publications

(3 citation statements)

References 50 publications

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“…[ 29 ] Orbscan is a reliable technique for the evaluation of the cornea and has been successfully used to refine the ablation profiles during LASIK, assess displacement of corneal surfaces after kerato-refractive procedures, monitor ectasia, and show ethnic differences in the incidence of keratoconus and monitor astigmatic changes after phacotrabeculectomy. [ 17 30 31 32 33 34 35 36 ]…”

Section: Discussionmentioning

confidence: 99%

The influence of routine uncomplicated phacoemulsification on the orthogonality of the cornea

Tutchenko

Patel

Voytsekhivskyy

et al. 2021

Indian Journal of Ophthalmology

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Purpose: The aim of this study was to determine the effect of routine uncomplicated phacoemulsification on the orthogonal distribution of mass within the central optical zone of the cornea. Methods: Astigmatism at both corneal surfaces was evaluated using Orbscan II (Bausch &and Lomb) before and up to 3 months after routine phacoemulsification (one eye/patient). The data were subjected to vector analysis to estimate the pre-and postoperative total astigmatism of the cornea (TCA). Results: Reporting the chief findings in minus cylinder (diopters, DC) over the central 3 mm (A) and 5 mm (B) optical zones. Mean TCA powers (±sd) at pre- and 3-months postop were A) –4.45DC (±2.00) and –5.69DC (±2.69), B) –2.91DC (±2.22) and –2.71DC (±1.60). Change in mean power was significant over 3 mm ( P < 0.01, n = 49) but not over 5 mm. Inter-zonal differences were significant ( P < 0.01). There was a significant linear relationship between the change in TCA power ( y = preoperative-postoperative) and TCA at preoperative stage (x) where, A) y = 0.45x + 3.12 ( r = 0.336, n = 49, P = 0.018), B) y = x + 2.65 ( r = 0.753, n = 49, P = <0.01). Over the central 3 mm zone only, change (preoperative-postoperative) in axis (°) of TCA (y 1 ) was significantly associated with TCA axis at preoperative stage (x 1 ) where y 1 = 1.391x 1 -0.008x 1 2 -0.701 ( r = 0.635, n = 49, P < 0.01). Conclusion: Changes in TCA power and axis at 3 months postop, determined using Orbscan II, are indicative of orthogonal alterations in the distribution of corneal tissue. Over the central 3 mm zone, the association between y 1 and x 1 shows that a change in TCA axis is more profound when preoperative axis is near 90° i.e., against-the-rule.

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Section: Discussionmentioning

confidence: 99%

The influence of routine uncomplicated phacoemulsification on the orthogonality of the cornea

Tutchenko

Patel

Voytsekhivskyy

et al. 2021

Indian Journal of Ophthalmology

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“…Full descriptions of the more widely available systems can be found in a range of review articles and numerous websites. [44][45][46][47][48] These radii are converted into power values, using the standard lens surface formula, assuming the refractive indices of the cornea and aqueous humour are 1.376 and 1.336, respectively. When the orthogonal radii of the corneal back surface are 5.8mm and 6.8mm the corresponding respective powers are −6.90D and −5.88D.…”

Section: Current Approaches For the Assessment Of Back Corneal Astigmatismmentioning

confidence: 99%

Spotlight on the Corneal Back Surface Astigmatism: A Review

Patel¹,

Tutchenko²

2021

OPTH

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Recent evidence indicates that the corneal back surface astigmatism (CBSA) contributes to the refractive state of the eye in cataract surgery, especially with the implantation of toric intraocular lenses. But this has been met with some scepticism. A review of key studies performed over the past three decades shows that the mean CBSA power ranges from 0.18(±0.16)D to 1.04(±0.20)D. The clinical assessment of CBSA is problematic. There is poor agreement between the current automated systems for assessment of CBSA and it is assumed that these systems directly measure the CBSA. But CBSA cannot be measured directly in vivo. A historical review of methods used to quantify the curvature of the posterior corneal surface reveals that CBSA estimated by current systems is based on values for corneal front surface astigmatism, corneal refractive index, central corneal thickness, corneal thickness at peripheral locations and the exact distance between the corneal apex and each one of these peripheral locations. Doubts and errors in these values, coupled with the precise details of the algorithm incorporated to estimate CBSA, are the likely sources of the lack of agreement between current systems. These systematic errors cloud the assessment of CBSA. Mean CBSA may be low, but it varies from case to case. There is a clear need for a realistic, practical procedure for clinicians to independently calibrate systems for estimating CBSA. This would help to reduce uncertainty and the discrepancies between instruments designed to measure the same parameter.

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“…is is a long-standing instrument proven to be useful for examining the corneal surfaces in a wide range of studies [11,[28][29][30][31][32][33]. Refractive astigmatism was determined by autorefractometry and by routine subjective refraction.…”

Section: Measurement Of Corneal Surfaces and Refractivementioning

confidence: 99%

The Impact of Changes in Corneal Back Surface Astigmatism on the Residual Astigmatic Refractive Error following Routine Uncomplicated Phacoemulsification

Tutchenko

Patel

Voytsekhivskyy

et al. 2020

Journal of Ophthalmology

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Purpose. To determine the significance of any association between intersessional changes in ocular residual astigmatism (RA) and astigmatism at corneal front (FSA) and back (BSA) surfaces following uneventful routine phacoemulsification. Methods. Astigmatism was evaluated by autorefractometry and subjective refraction and at both the corneal surfaces with Orbscan II™ (Bausch & Lomb) over central 3 mm and 5 mm optical zones at 1, 2, and 3 months after routine phacoemulsification in 103 patients implanted with monofocal nontoric intraocular lenses (IOLs, one eye/patient). Data were subjected to vector analysis to determine the actual change (Δ) in astigmatism (power and axis) for the refractive and Orbscan II findings. Results. The number of cases that attended where ΔRA was ≥0.50 DC between 1 and 2 months was 52 by autorefractometry and 36 by subjective refraction and between 2 and 3 months was 24 by autorefractometry and 19 by subjective refraction. Vector analysis revealed significant correlations between ΔFSA and ΔRA for data obtained by autorefractometry but not by subjective refraction. At all times, ΔBSA was greater than ΔFSA (p<0.01). Key findings for ΔBSA values over the central 3 mm zone were between (A) the sine of the axis of ΔRA (y) and sine of the axis of ΔBSA (x) for the data obtained by autorefractometry (between 1 and 2 months, y = 0.749 − 0.303x, r = 0.299, n = 52, p=0.031) and subjective refraction (between 2 and 3 months, y = 0.6614 − 0.4755x, r = 0.474, n = 19, p=0.040) and (B) ΔRA (y) and ΔBSA (x) powers between 2 and 3 months postoperatively for the data obtained by autorefractometry (ΔRA = 0.118 ΔBSA + 0.681 r = 0.467, n = 24, p=0.021) and subjective refraction (ΔRA = 0.072 ΔBSA + 0.545 r = 0.510, n = 19, p=0.026). Conclusion. Changes in the ocular residual refractive astigmatic error after implanting a monofocal nontoric IOL are associated with changes in astigmatism at the back surface of the cornea within the central optical zone.

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Developments in diagnostic tools for corneal ectasia

Cited by 4 publications

References 50 publications

The influence of routine uncomplicated phacoemulsification on the orthogonality of the cornea

The influence of routine uncomplicated phacoemulsification on the orthogonality of the cornea

Spotlight on the Corneal Back Surface Astigmatism: A Review

The Impact of Changes in Corneal Back Surface Astigmatism on the Residual Astigmatic Refractive Error following Routine Uncomplicated Phacoemulsification

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