Objective To assess a new method to measure the distance of the needle passage from the ciliary sulcus to the corneal limbus anterior border (CTC) in eyes with ectopia lentis directly in vivo via endoscopy and to further evaluate the correlations among the CTC, age, automated horizontal white-to-white distance (WTW), and ocular axial length (AL). Methods The WTW and AL were measured using an optical biometer. An intraocular endoscope was used during transscleral suture fixation of posterior chamber intraocular lenses to identify the true location of the ciliary sulcus. Linear regression analysis was used to assess the correlation between the CTC and other ocular biological parameters, including age, WTW, and AL. Results Thirty eyes of 30 children with ectopia lentis were evaluated. A statistically significant correlation was found between age and the CTC. The CTC could be predicted by the equation CTC = 0.1313 × Age + 0.9666. No statistically significant correlations were found between CTC and WTW, CTC and AL, WTW and AL, or WTW and age. Conclusion Endoscopy is useful for precisely suturing intraocular lens haptics in the real ciliary sulcus. Age can be used as an equivalent parameter for prediction of the true ciliary sulcus location.