Use of Axial Length to Estimate the Vitreous Chamber Volume in Pseudophakic

To develop an equation for estimating the vitreous chamber volume in pseudophakic patients based on the axial length of the eye. A consecutive series of patients who underwent vitrectomy surgery for a macular hole or an epiretinal membrane were enrolled. The inclusion criteria were as follows: having pseudophakia, being older than 50 years, and having eyes with axial length ranging from 21 to 26 mm. Before the surgery, the axial length was measured using optical biometry. Pars plan vitrectomy was performed, and, after the fluid-air exchange, the vitreous chamber was filled with Brilliant Blue G (0.005%). The infused volume of each eye was recorded. Then, epiretinal membrane peeling or internal limiting membrane peeling and a new fluid-air exchange were performed. Main outcomes and measures were the vitreous chamber volume and axial length. The sample consisted of 112 patients. The mean [standard deviation (SD), range] age was 71 years (7, 53–90). Sixty-five individuals (58%) were women. In 58 (51.8%) patients, surgery was performed on the right eye. The mean (SD; range) axial length was 23.78 mm (0.93; 21.55–25.26), and the mean (SD; range) vitreous chamber volume was 4.96 mL (0.69; 3.60—6.40). Pearson’s correlation coefficient (r = 0.950; p < 0.01) was positive, and the coefficient of determination (R2) was 0.902. The estimated regression equation was Y = 0.71X − 11.84, where Y was the vitreous chamber volume, X was the axial length of the eye, the linear coefficient for the straight line was − 11.83, and the angular coefficient was 0.71 (p < 0.01). These data suggest that the vitreous chamber volume is significantly correlated with the axial length and the former could probably be calculated using biometry. New studies with larger samples will be required to confirm these observations and will allow the development of an algorithm (perhaps non-linear) that includes extreme axial length values and that takes into account other factors such as the status of the lens and sex.