Corneal Power Estimation Using Orbscan II Videokeratography in Eyes With Previous Corneal Refractive Surgeries

Dong Hyun Jo; Joo Youn Oh; Mee Kum Kim; Jin Hak Lee; Won Ryang Wee

doi:10.3341/jkos.2009.50.11.1730

Journal List > J Korean Ophthalmol Soc > v.50(11) > 1008429

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Jo, Oh, Kim, Lee, and Wee: Corneal Power Estimation Using Orbscan II Videokeratography in Eyes With Previous Corneal Refractive Surgeries

Original Article

J Korean Ophthalmol Soc 2009;50(11):1730-1734.

Published online: 31 August 2009

DOI: https://doi.org/10.3341/jkos.2009.50.11.1730

Corneal Power Estimation Using Orbscan II Videokeratography in Eyes With Previous Corneal Refractive Surgeries

Dong Hyun Jo, MD¹, Joo Youn Oh, MD, PhD¹, Mee Kum Kim, MD, PhD^1,², Jin Hak Lee, MD, PhD^1,², Won Ryang Wee, MD, PhD^1,²

¹Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Korea

²Seoul Artificial Eye Center, Seoul National University Hospital Clinical Research Institute, Seoul, Korea

Address reprint requests to Won Ryang Wee, MD, PhD, Department of Ophthalmology, Seoul National University College of Medicine #28 Yeongeon-dong, Jongno-gu, Seoul 110-744, Korea Tel: 82-2-2072-2435, Fax: 82-2-741-3187, E-mail: wrwee@snu.ac.kr

Received 29 April 2009 Accepted 4 August 2009

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose

To report three cases of corneal power estimation for intraocular lens power calculation using Orbscan II videokeratography in eyes with previous corneal refractive surgeries.

Case summary

In three eyes of three patients with previous corneal refractive surgeries, corneal power values were respectively measured at three, four, five, six mm-diameter zones of total mean, axial, tangential, and optical maps using Orbscan II videokeratography. Then, intraocular lens power values were calculated via the SRK/T formula. After cataract surgeries, back-calculated corneal power (BCK) values were estimated from post-phacoemulsification refraction data, and compared with those measured at three, four, five, six mm-diameter zones of each map in Orbscan II videokeratography. The postoperative refractive values after cataract surgeries were achieved within 1.5D of the target refraction in all eyes by using five mm total axial power and four mm total optical power for intraocular lens power calculation. Orbscan II parameters including three mm, four mm total axial power, and three mm total optical power were the least different from the BCK (0.69±0.49D, 1.08±0.54D, and 1.10±0.44D, respectively).

Conclusions

If historical data are not available, Orbscan II videokeratography can be useful for estimating corneal power for intraocular lens power calculations in patients with previous corneal refractive surgeries.

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Keywords: Cataract surgery, Corneal refractive surgery, Intraocular lens, IOL power calculation, Orbscan videokeratography

References

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Table 1.

Demographic data and clinical features

Characteristics	Case 1	Case 2	Case 3
Age (years)	51	63	42
Laterality	Right	Right	Right
Type of corneal refractive surgery	LASIK^*	LASIK	PRK^†
Interval between LASIK/PRK and cataract surgery (months)	37	132	240
Pre-cataract surgery spherical equivalent (diopters)	−8.5	−2.375	N/A^‡
UCVA^§ before cataract surgery (20/)	300	200	200
BCVA^∏ before cataract surgery (20/)	30	N/A	N/A
Axial length (mm)	26.73	25.8	26.36

^*LASIK=laser in situ keratomileusis

^†PRK=photorefractive keratectomy

^‡not available due to white cataract

^§UCVA=uncorrected visual acuity

^∏BCVA=best corrected visual acuity.

Table 2.

The Orbscan-derived keratometric values from 4 different power maps

	Case 1	Case 2	Case 3
Simulated K readings	38.4	41.8	41.5
3 mm zone	38.6	42.3	42.3
5 mm zone	41.9	43.6	43.4
Total mean power 3 mm	36.5317	40.3211	39.75
Total mean power 4 mm	37.4052	41.1473	40.8533
Total mean power 5 mm	39.0093	42.3808	41.6714
Total mean power 6 mm	40.7298	43.4473	41.9979
Total axial power 3 mm	35.8777	39.9967	38.287
Total axial power 4 mm	36.1463	40.1269	39.0487
Total axial power 5 mm	36.6661	40.6061	39.8009
Total axial power 6 mm	37.5603	41.2601	40.4422
Total tangential power 3 mm	36.641	39.7226	40.304
Total tangential power 4 mm	37.4911	41.2387	42.1397
Total tangential power 5 mm	40.1504	43.395	43.4647
Total tangential power 6 mm	43.366	45.6863	43.6561
Total optical power 3 mm	36.2351	40.4386	38.7261
Total optical power 4 mm	36.5944	40.7015	39.6429
Total optical power 5 mm	37.2758	41.4137	40.6279
Total optical power 6 mm	38.4543	42.3911	41.5681

Table 3.

Comparison of target refraction and real refraction after cataract surgery

	Case 1	Case 2	Case 3
Target refraction (D)	0	0	−1.5
Spherical equivalent 1 week after surgery (D)	1.75	0.25	N/A
Spherical equivalent 1 month after surgery (D)	1.125	0	0
Difference between target and real refraction (D)	1.125	0	1.5

Table 4.

Comparison of back-calculated keratometric value (BCK) value and Orbscan II parameters (Orbscan II parameters –BCK value)

		Case 1	Case 2	Case 3	Average
Total mean power	3 mm	+1.9017	+0.6711	+1.94	+1.50
	4 mm	+2.7752	+1.4973	+3.0433	+2.43
	5 mm	+4.3793	+2.7308	+3.8614	+3.65
	6 mm	+6.0998	+3.7973	+4.1879	+4.69
Total axial power	3 mm	+1.2477	+0.3467	+0.477	+0.69
	4 mm	+1.5163	+0.4769	+1.2387	+1.07
	5 mm	+2.0361	+0.9561	+1.9909	+1.66
	6 mm	+2.9303	+1.6101	+2.6322	+2.39
Total tangential power	3 mm	+2.011	+0.0726	+2.494	+1.52
	4 mm	+2.8611	+1.5887	+4.3297	+2.92
	5 mm	+5.5204	+3.745	+5.6547	+4.97
	6 mm	+8.736	+6.0363	+5.8461	+6.87
Total optical power	3 mm	+1.6051	+0.7886	+0.9161	+1.10
	4 mm	+1.9644	+1.0515	+1.8329	+1.61
	5 mm	+2.6458	+1.7637	+2.8179	+2.40
	6 mm	+3.8243	+2.7411	+3.7581	+3.44

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