Purpose: We present a novel technique for measuring volume of space replaced by air during fluid-air exchange in vitrectomy (vitrectomized space) for intravitreal gas injection. To confirm the feasibility of this technique, we assessed postoperative intraocular pressure (IOP) and the duration of injected gas. Using this technique, we found remarkable differences in volume between high myopic eyes with retinal detachment caused by peripheral break (PB-RD group) and those with macular hole retinal detachment (MH-RD group). We studied the relationships between the volume and biometric values, axial length (AL) and corneal curvature radius (CCR) in both PB-RD and MH-RD group. Study design: Retrospective study. Methods: During fluid-air exchange, the aspirated fluid accumulates in the measuring cup between the infusion needle and vitrectomy instrument. Vitrectomized space volume is obtained by subtracting the volume of the tube between the infusion needle and the 3-way stopcock from the aspirated fluid volume. We performed phaco-vitrectomies by measuring the vitrectomized space volume and then injected pure SF6 at 15% of the volume into the vitreous cavity in 156 myopic eyes (AL > 26 mm) with RD consisting of 144 eyes in PB-RD group and 12 in MH-group. Results: The IOP (mean ± SD) was 13.5 ± 3.4 mmHg preoperatively, 23.4 ± 10.4 mmHg on day 1, 18.2 ± 7.4 mmHg on day 2, and 16.1 ± 4.5 on day 7. The gas disappeared in 16.1 ± 1.9 days. Axial length was longer in the MH-RD group but the volume of vitrectomized space was larger in the PB-RD group. AL and volume were significantly correlated in both groups (P < 0.01), but the fitting lines differed. The CCR and volume significantly correlated in the PB-RD group (P < 0.01) but not in the MH-RD group. Conclusion: Our novel technique for measuring the volume of vitrectomized space can achieve target gas concentration in the vitreous cavity. The difference in the shape of eyeballs may explain discrepancies in relationship between volume and the biometric factors.
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