Consider Patient Age When Calculating IOL Power, Study Suggests

Norra MacReady

October 13, 2016

Refractive prediction error (PE) changes with a patient's age, according to results from a prospective, cohort study. The researchers suggest patient age should be taken into account when determining intraocular lens (IOL) power for cataract surgery.

In addition to age, the authors also found that preoperative axial length (AL), anterior chamber depth (ACD; effective lens position), and average keratometry readings (K values) were significant independent predictors of PE.

On the basis of these findings, lead author Ken Hayashi, MD, and coauthors recommend that "the A-constants for the SRK/T formula should be slightly modified according to a patient's age at the time of surgery," in an article published in the October issue of the American Journal of Ophthalmology.

PE is the most common complication of cataract extraction and IOL insertion, Dr Hayashi, from the Hayashi Eye Hospital, Fukuoka, Japan, and colleagues note. Because ocular biometry measurements, including AL, corneal curvature, and estimated postoperative ACD, all increase with age, they hypothesize that age may influence PE as well.

The authors analyze data and outcomes for consecutive patients stratified by age: 60 to 69 years, 70 to 79 years, and 80 to 89 years. There were 150 eyes in each group. The control group consisted of 75 eyes in patients aged 59 years of age or younger. Dr Hayashi performed all of the surgeries. Patients were examined immediately postoperatively and approximately 3 months later. IOL power was calculated using the standard SRK/T formula with optimized A-constants.

The 525 patients had a mean age of 71.6 years (standard deviation [SD], ±9.3 years) and included 347 women (66.1%). The mean preoperative manifest spherical equivalent value (MRSE) was significantly less myopic with age, at −1.19 ± 3.22 diopters (D) among patients 60 to 69 years of age, −0.27 ± 1.91 D among patients 70 to 79 years of age, and −0.00 ± 1.33 D among patients 80 to 89 years of age compared with −2.18 ± 2.86 D among patients aged 50 to 59 years of age (P < .0001 between all groups).

The preoperative target refraction was not significantly different between the groups, at −0.31 ± 0.15 D for patients in the 60- to 69- and 70- to 79-year age groups, −0.31 ± 0.18 D for patients aged 80 to 89 years, and −0.28 ± 0.15 D for patients 59 years of age or younger (P = .4763).

Three months postoperatively, the mean MRSE was −0.48 ± 0.36 D in the 60- to 69-year age group, −0.42 ± 0.38 D among patients 70 to 79 years of age, and −0.36 ± 0.39 D among patients 80 to 89 years of age compared with −0.52 ± 0.39 D in the control group. The differences were statistically significant between all age groups (P = .0102).

The mean PE 3 months postoperatively was −0.24 ± 0.36 D, −0.17 ± 0.35 D, −0.11 ± 0.36 D, and −0.05 ± 0.39 D, respectively, among patients ≤59 years, 60 to 69 years, 70 to 79 years, and 80 to 89 years of age.

"The mean arithmetic PE was less myopic by approximately 0.06 diopter per decade of increased age (P = .0010)," the authors write. This relationship persisted even when eyes with unusually short or long AL were excluded from the analysis. A correlation analysis also showed a significant association between the arithmetic PE and greater age (Pearson r = 0.177; P < .0001).

PE was not associated with preoperative AL, ACD, or K values. However, in multiple linear regression analysis, preoperative AL (regression coefficient, −0.106; standard error, 0.021), ACD (regression coefficient, 0.225; standard error, 0.046), and average K values (regression coefficient, −0.106; standard error, 0.013) all were significant independent predictors of PE (P < .0001 for all values).

Overall, the mean spherical and cylindrical refractive power values showed a significant increase with age (P < .0001). Age also was associated with significant AL shortening and increasing ACD shallowness, and showed a weak but significant association with a flatter corneal curvature.

Recent efforts to diminish PE include adjusting the standard formulas and use of developments such as the Holladay 2 or Haigis-L formulas in IOL power calculations, the authors write. "Although these efforts have improved refractive outcomes in modern cataract surgery, patient age should also be taken into consideration to determine the precise IOL power." Specifically, they recommend modifying the A-constants for the SRK/T formula to reflect the patient's age.

However, they warn, it is uncertain "whether the age-related difference in PE holds true in eyes for which the IOL power was calculated using other formulas."

One or more study authors reports receiving research grants from Alcon Japan Ltd, Santen Pharmaceutical Inc, Abbot Medical Optics, HOYA Corporation, and Wakamoto Pharmaceutical Ltd.

Am J Ophthalmol. 2016;170:232-237. Full text

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