Abstract
Purpose:
Accurate axial length measurement is critical in gauging myopic progression. Partial coherence interferometry used in machines such as the Zeiss IOLMaster is the most commonly used method in clinical ophthalmology for measuring axial length. Due to irregularities of slope and shape in the posterior wall of staphylomatous eyes, aberrant reflections are possible and can result in inaccurate measurements. This present work compares IOLMaster-measured axial lengths and manually measured axial lengths on 3-D MRI volume renderings in highly myopic patients with staphyloma to determine if the difference between the two measurements is affected by the eye axial length.
Methods:
A prospective study was performed on 34 eyes of 17 patients which included 8 eyes of 4 emmetropic volunteers and 26 eyes of 13 high myopia patients clinically diagnosed with staphyloma. All eyes underwent measurement with both IOLMaster and 3-D MRI scan (Phillips, 3.0T, fat-suppressed T2-weighted cube, a modified 3-D fast-spin echo sequence). Volume renderings of the eyes were generated from high-resolution 3-D data and properly oriented so the eye could be rotated around its visual axis. MRI axial length (from the posterior cornea to the vitreo-retinal interface) was manually measured from 4 different views (each 90 degrees apart) and averaged. Axial length measurement with IOLMaster was compared to that found with the 3-D MRI rendering of the eye. Univariate regression analysis was used to correlate the absolute difference between the two measurement modalities and axial length as measured by each of the two devices.
Results:
Eyes examined ranged in axial length from 21.62 to 39.32 mm on IOLMaster and from 21.69 to 39.31 mm on MRI. The axial length measured by IOLMaster was longer than that measured by MRI in 25 out of 26 eyes (96%) among high myopia patients and 4 out of 8 emmetropic patients (50%). Linear regression did not show an association between the absolute difference between the two measurement modalities and axial length as measured by MRI (p = 0.511) or IOLMaser (p= 0.767).
Conclusions:
Assessment of axial length in staphylomatous eyes may be challenging, potentially influenced by staphyloma location and local slope. Initial studies suggest that differences in axial length measured by IOLMaster versus MRI is not influenced by the magnitude of axial length.