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Refractive cylinder outcomes after calculating toric intraocular lens cylinder power using total corneal refractive power.

Davison JA, Potvin R - Clin Ophthalmol (2015)

Bottom Line: Vector differences between expected and actual residual refractive cylinder were calculated and compared to simulated vector errors using the collected VERION keratometry data.The TCRP-based calculation resulted in a statistically significantly lower vector error (P<0.01) and significantly more eyes with a vector error ≤0.5 D relative to the VERION-based calculation (P=0.02).Using the TCRP keratometry measurement in the AcrySof toric calculator may improve overall postoperative refractive results.

View Article: PubMed Central - PubMed

Affiliation: Wolfe Eye Clinic, Marshalltown, IA, USA.

ABSTRACT

Purpose: To determine whether the total corneal refractive power (TCRP) value, which is based on measurement of both anterior and posterior corneal astigmatism, is effective for toric intraocular lens (IOL) calculation with AcrySof(®) Toric IOLs.

Patients and methods: A consecutive series of cataract surgery cases with AcrySof toric IOL implantation was studied retrospectively. The IOLMaster(®) was used for calculation of IOL sphere, the Pentacam(®) TCRP 3.0 mm apex/ring value was used as the keratometry input to the AcrySof Toric IOL Calculator and the VERION™ Digital Marker for surgical orientation. The keratometry readings from the VERION reference unit were recorded but not used in the actual calculation. Vector differences between expected and actual residual refractive cylinder were calculated and compared to simulated vector errors using the collected VERION keratometry data.

Results: In total, 83 eyes of 56 patients were analyzed. Residual refractive cylinder was 0.25 D or lower in 58% of eyes and 0.5 D or lower in 80% of eyes. The TCRP-based calculation resulted in a statistically significantly lower vector error (P<0.01) and significantly more eyes with a vector error ≤0.5 D relative to the VERION-based calculation (P=0.02). The TCRP and VERION keratometry readings suggested a different IOL toric power in 53/83 eyes. In these 53 eyes the TCRP vector error was lower in 28 cases, the VERION error was lower in five cases, and the error was equal in 20 cases. When the anterior cornea had with-the-rule astigmatism, the VERION was more likely to suggest a higher toric power and when the anterior cornea had against-the-rule astigmatism, the VERION was less likely to suggest a higher toric power.

Conclusion: Using the TCRP keratometry measurement in the AcrySof toric calculator may improve overall postoperative refractive results. Consideration of measured posterior corneal astigmatism, rather than a population-averaged value, appears advantageous.

No MeSH data available.


Related in: MedlinePlus

Calculating vector errors.Notes: Calculating vector errors with the actual manifest refractive astigmatism (A), or simulated manifest refractive astigmatism (C), the latter based on the simulated astigmatism derived in (B). The numerals indicate the steps in the calculation.Abbreviation: IOL, intraocular lens.
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f2-opth-9-1511: Calculating vector errors.Notes: Calculating vector errors with the actual manifest refractive astigmatism (A), or simulated manifest refractive astigmatism (C), the latter based on the simulated astigmatism derived in (B). The numerals indicate the steps in the calculation.Abbreviation: IOL, intraocular lens.

Mentions: Analysis included a summary of the postoperative refractive status of all eyes as determined by manifest refraction. The vector error in the actual (TCRP-based) toric IOL result was calculated by comparing actual achieved versus expected residual refractive cylinder provided by the toric IOL calculator. Figure 2A illustrates the vector components of such a calculation. In addition to the actual TCRP versus expected calculation, a simulation of results with a second calculation was performed using a technique described by Hill et al.14 To achieve this comparison, the actual IOL implanted using the TCRP data was mathematically “removed” and the IOL suggested by the AcrySof toric calculator using the VERION data was mathematically “implanted”. Figure 2B illustrates the vector effect of this “simulated replacement”. When that replacement was completed, a new residual refractive error and expected residual astigmatism from the AcrySof toric calculator using VERION data were derived and then used to calculate a new vector error of simulated actual achieved versus expected as shown in Figure 2C. The method of back-calculation of the toric IOL power was based on the method of Fam and Lim.15 The vector errors from the actual versus VERION-based calculations were compared with cylinder orientation as a categorical variable (WTR, oblique [OBL], ATR); a steep corneal meridian within 30 degrees of vertical was considered WTR, a steep corneal meridian within 30 degrees of horizontal was considered ATR, and the 30 degrees in between was considered OBL.


Refractive cylinder outcomes after calculating toric intraocular lens cylinder power using total corneal refractive power.

Davison JA, Potvin R - Clin Ophthalmol (2015)

Calculating vector errors.Notes: Calculating vector errors with the actual manifest refractive astigmatism (A), or simulated manifest refractive astigmatism (C), the latter based on the simulated astigmatism derived in (B). The numerals indicate the steps in the calculation.Abbreviation: IOL, intraocular lens.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4548767&req=5

f2-opth-9-1511: Calculating vector errors.Notes: Calculating vector errors with the actual manifest refractive astigmatism (A), or simulated manifest refractive astigmatism (C), the latter based on the simulated astigmatism derived in (B). The numerals indicate the steps in the calculation.Abbreviation: IOL, intraocular lens.
Mentions: Analysis included a summary of the postoperative refractive status of all eyes as determined by manifest refraction. The vector error in the actual (TCRP-based) toric IOL result was calculated by comparing actual achieved versus expected residual refractive cylinder provided by the toric IOL calculator. Figure 2A illustrates the vector components of such a calculation. In addition to the actual TCRP versus expected calculation, a simulation of results with a second calculation was performed using a technique described by Hill et al.14 To achieve this comparison, the actual IOL implanted using the TCRP data was mathematically “removed” and the IOL suggested by the AcrySof toric calculator using the VERION data was mathematically “implanted”. Figure 2B illustrates the vector effect of this “simulated replacement”. When that replacement was completed, a new residual refractive error and expected residual astigmatism from the AcrySof toric calculator using VERION data were derived and then used to calculate a new vector error of simulated actual achieved versus expected as shown in Figure 2C. The method of back-calculation of the toric IOL power was based on the method of Fam and Lim.15 The vector errors from the actual versus VERION-based calculations were compared with cylinder orientation as a categorical variable (WTR, oblique [OBL], ATR); a steep corneal meridian within 30 degrees of vertical was considered WTR, a steep corneal meridian within 30 degrees of horizontal was considered ATR, and the 30 degrees in between was considered OBL.

Bottom Line: Vector differences between expected and actual residual refractive cylinder were calculated and compared to simulated vector errors using the collected VERION keratometry data.The TCRP-based calculation resulted in a statistically significantly lower vector error (P<0.01) and significantly more eyes with a vector error ≤0.5 D relative to the VERION-based calculation (P=0.02).Using the TCRP keratometry measurement in the AcrySof toric calculator may improve overall postoperative refractive results.

View Article: PubMed Central - PubMed

Affiliation: Wolfe Eye Clinic, Marshalltown, IA, USA.

ABSTRACT

Purpose: To determine whether the total corneal refractive power (TCRP) value, which is based on measurement of both anterior and posterior corneal astigmatism, is effective for toric intraocular lens (IOL) calculation with AcrySof(®) Toric IOLs.

Patients and methods: A consecutive series of cataract surgery cases with AcrySof toric IOL implantation was studied retrospectively. The IOLMaster(®) was used for calculation of IOL sphere, the Pentacam(®) TCRP 3.0 mm apex/ring value was used as the keratometry input to the AcrySof Toric IOL Calculator and the VERION™ Digital Marker for surgical orientation. The keratometry readings from the VERION reference unit were recorded but not used in the actual calculation. Vector differences between expected and actual residual refractive cylinder were calculated and compared to simulated vector errors using the collected VERION keratometry data.

Results: In total, 83 eyes of 56 patients were analyzed. Residual refractive cylinder was 0.25 D or lower in 58% of eyes and 0.5 D or lower in 80% of eyes. The TCRP-based calculation resulted in a statistically significantly lower vector error (P<0.01) and significantly more eyes with a vector error ≤0.5 D relative to the VERION-based calculation (P=0.02). The TCRP and VERION keratometry readings suggested a different IOL toric power in 53/83 eyes. In these 53 eyes the TCRP vector error was lower in 28 cases, the VERION error was lower in five cases, and the error was equal in 20 cases. When the anterior cornea had with-the-rule astigmatism, the VERION was more likely to suggest a higher toric power and when the anterior cornea had against-the-rule astigmatism, the VERION was less likely to suggest a higher toric power.

Conclusion: Using the TCRP keratometry measurement in the AcrySof toric calculator may improve overall postoperative refractive results. Consideration of measured posterior corneal astigmatism, rather than a population-averaged value, appears advantageous.

No MeSH data available.


Related in: MedlinePlus