Optical versus Ultrasonographic Axial Length Measurement before Cataract Surgery: A Comparison across Short, Normal and Long Eyeballs.

Inaccurate biometry results can cause the worst postoperative visual outcome. An error of 1mm in the axial length measurement causes a refractive error of 2.5 D in an average eye of 23.5 mm, 1.75 D in 30 mm and 3.75 D in a 20 mm eye. The difference is much more in very short eyes. Now the result of this study will guide our clinicians to get a better biometry result in the case of short, normal and long eyeballs. The study was conducted to compare the difference in axial length measurement done by A-scan ultrasonogram and IOLMaster 700 before cataract surgery among short, normal and long eyeballs. This was a cross-sectional type of observational study. The study was conducted purposively among the age-related cataract patients admitted into the department of Ophthalmology, Mymensingh Medical College and Hospital, Bangladesh from April 2019 to March 2022. Eyeballs were categorized according to axial length as short, normal and long. Among the subgroups, axial length in short eyeballs was <22mm, normal eyeballs were 22-24mm and long eyeballs were >24mm. A total of 254 eyes of 254 age-related cataract patients were included in this study. The mean age of the total study patients was 62.32±8.48 years. A maximum of 51.6% of patients belonged to age 60-69 years and a minimum of 80-89 years. Among the study population, 50.4% of the patients were female and 49.6% of the patients were male. Eyeballs were categorized according to AL as short in 33(13.0%), normal in 196(77.2%) and long in 25(9.8%) patients. For short eyes, the mean±SD of AL measured with A-scan and IOLMaster were 21.27±0.48 mm and 21.68±0.41 mm respectively with a mean difference of 0.42±0.26 mm. For normal eyes, mean±SD AL measured with A-scan and IOLMaster was 22.66±0.45 mm and 23.04±0.48 mm respectively with a mean difference of 0.38±0.22 mm. For long eyes, mean±SD AL measured with A-scan and IOLMaster was 24.20±0.28 mm and 24.43±0.37 mm respectively with a mean difference of 0.23±0.42 mm. Among 254 patients, the mean±SD AL with A scan and IOLMaster was 22.63±0.82 mm and 23.00±0.80 mm respectively with a mean difference of 0.37±0.26 mm. The AL measured by IOLMaster was significantly more accurate (p= <0.001) than that measured by A-scan among all the subgroups as well as total eyeballs. The analysis showed good agreement between IOLMaster and A-scan. Axial length measurement by IOLMaster was more than A scan with a statistically significant difference (p= <0.001). The difference was more in short eyeballs and less in long eyeballs than normal. A correction factor of 0.37 mm can be added to A-scan ultrasonogram to get near-accurate axial length like optical biometry.