IOL Calculations Based on Partial Biometry in Humanitarian Missions Joseph Schmitz, MD Kimberly Davis, MD, FACS Scott McClatchey, MD The authors have no financial interest in the subject matter of this poster The views expressed in this presentation are those of the authors and do not reflect the official policy or position of the Department of the Navy, Department of Defense, or the United States Government

Introduction Complete biometry, including both axial length (AL) and corneal power (K), is not always available for intraocular lens (IOL) calculations on humanitarian (HA) missions Complete biometry, including both axial length (AL) and corneal power (K), is not always available for intraocular lens (IOL) calculations on humanitarian (HA) missions Due to time and resource limitations of HA missions or lens density, a surgeon may be required to proceed with IOL selection with incomplete data Due to time and resource limitations of HA missions or lens density, a surgeon may be required to proceed with IOL selection with incomplete data

Introduction (continued) Without AL or K, proposed methods for IOL selection include: Without AL or K, proposed methods for IOL selection include: 1) Use of the mean population emmetropic IOL power 2) Substitution of the mean population K or AL for the unknown measurement 3) Use of a documented correlation between AL and K to calculate the unknown measurement

Purpose To determine the correlation between axial length (AL), corneal power (K), and population data in the developing nations served by humanitarian missions between 2007 and 2008 To determine the correlation between axial length (AL), corneal power (K), and population data in the developing nations served by humanitarian missions between 2007 and 2008 To determine the most accurate IOL power calculation method in settings of partial biometry To determine the most accurate IOL power calculation method in settings of partial biometry

Methods Retrospective chart review of all 295 adult patients with biometry measurements obtained during United States Navy HA missions in Southeast Asia between in 2007 and 2008 Retrospective chart review of all 295 adult patients with biometry measurements obtained during United States Navy HA missions in Southeast Asia between in 2007 and 2008 Correlation between AL and mean K by linear regression was calculated Correlation between AL and mean K by linear regression was calculated Formula for estimating K based on AL was derived with Deming Regression Analysis Formula for estimating K based on AL was derived with Deming Regression Analysis IOL power for emmetropia for each eye was calculated from the measured AL and measured mean K IOL power for emmetropia for each eye was calculated from the measured AL and measured mean K

Methods (continued) Theoretic refractive error based on five scenarios was calculated Theoretic refractive error based on five scenarios was calculated Estimated K and measured AL Estimated K and measured AL Measured K and estimated AL Measured K and estimated AL Measured K and mean population AL Measured K and mean population AL Mean population K and measured AL Mean population K and measured AL Mean population emmetropic IOL power Mean population emmetropic IOL power All IOL calculations used: All IOL calculations used: Holliday I formula Holliday I formula A-constant set at (the value for SA60 and MA60 acrylic lenses) A-constant set at (the value for SA60 and MA60 acrylic lenses)

Results Mean population Mean population AL mm AL mm K D K D IOL power for emmetropia D IOL power for emmetropia D AL showed a significant negative correlation with K (Correlation coefficient r = -0.58, R2 = 0.34, p <0.01) AL showed a significant negative correlation with K (Correlation coefficient r = -0.58, R2 = 0.34, p <0.01) Deming Regression Analysis (K =74.56 – x AL) Deming Regression Analysis (K =74.56 – x AL) The clinical measurements for AL and K were evaluated in a scatter plot (Figure 1-next slide) The clinical measurements for AL and K were evaluated in a scatter plot (Figure 1-next slide)

Figure 1- Clinical Measurements of Axial Length and Corneal Power

Results (continued) Mean absolute refractive error based on different methods of IOL calculation Mean absolute refractive error based on different methods of IOL calculation 1.91 D when using the measured K and estimated AL 1.91 D when using the measured K and estimated AL 0.90 D when using the estimated K and measured AL 0.90 D when using the estimated K and measured AL 1.11 D when using mean population K and measured AL 1.11 D when using mean population K and measured AL 1.55 D when using measured K and mean population AL 1.55 D when using measured K and mean population AL 1.22 D when using a mean population IOL power of 20.0 D 1.22 D when using a mean population IOL power of 20.0 D Table 1 (next slide) shows results by percentage of population within indicated diopters from emmetropia for the different methods of IOL calculation Table 1 (next slide) shows results by percentage of population within indicated diopters from emmetropia for the different methods of IOL calculation

Table 1 Total Percentage of Population Within Indicated Diopters From Emmetropia Absolute Diopter From Emmetropia AL estimated from measured K K estimated from measured AL Mean population (20 D) IOL Mean population K Mean population AL < < < < < < < <899.7 < <10100 Total percentage of population based on different scenarios for IOL calculation

Conclusion AL and K have a significant negative correlation If measured K values are unavailable, estimating K from AL results in significantly less refractive error than using either standard IOL power or substituting mean population K value If measured AL values are unavailable, than using standard IOL power results in significantly less refractive error than estimating K from AL or substituting mean population AL value Figure 2 (next slide) reveals an IOL flow diagram we recommend for best refractive results

Figure 2- Optimal IOL selection Review of AL and K measurement availability AL and K Use Standard IOL formula AL only Use correlation between population AL and K to estimate K K only Use mean population IOL