Investigation of intraocular pressure of the anterior chamber and vitreous cavity of porcine eyes via a novel method

Effect of twisting of intravitreal injections on ocular bio-mechanics: a novel insight to ocular surgery

Although intravitreal (IVT) injections provide several advantages in treating posterior segment eye diseases, several associated challenges remain. The current study uses the finite element method (FEM) to highlight the effect of IVT needle rotation along the insertion axis on the reaction forces and deformation inside the eye. A comparison of the reaction forces at the eye's key locations has been made with and without rotation. In addition, a sensitivity analysis of various parameters, such as the needle's angular speed, insertion location, angle, gauge, shape, and intraocular pressure (IOP), has been carried out to delineate the individual parameter's effect on reaction forces during rotation. Results demonstrate that twisting the needle significantly reduces the reaction forces at the penetration location and throughout the needle travel length, resulting in quicker penetration. Moreover, ocular biomechanics are influenced by needle insertion location, angle, shape, size, and IOP. The reaction forces incurred by the patient may be reduced by using a bevel needle of the higher gauge when inserted close to the normal of the local scleral surface toward the orra serrata within the Pars Plana region. Results obtained from the current study can deepen the understanding of the twisting needle's interaction with the ocular tissue.

Real-time in vivo monitoring of intraocular pressure distribution in the anterior chamber and vitreous chamber for diagnosis of glaucoma

Glaucoma causes irreversible vision loss due to optic nerve damage and retinal cell degeneration. Since high intraocular pressure (IOP) is a major risk factor for glaucoma development, accurate IOP measurement is crucial, especially intravitreal IOP affecting the optical nerve and cells. However, conventional methods have limits in selectively and directly detecting local retina pressure. Here, we present continuous measurements of local IOP values in the anterior chamber and vitreous chamber of living animals using minimally invasive probes with pressure-sensitive transistors. After inducing glaucoma in animal models, we compared the local IOP distribution between normal and glaucomatous eyes. We also compared IOP values detected in the cornea using tonometry measurements. Our findings revealed that glaucoma induced higher IOP in the vitreous chamber than in the anterior chamber, indicating that measuring IOP in the vitreous chamber is key to the glaucoma model. This progress offers future directions for diagnosis and treatment of glaucoma.

Measurement of vitreous humor pressure in vivo using an optic fiber pressure sensor

We conducted a study to assess the pressure difference between the aqueous and vitreous humors in rabbit eyes using a direct intraocular pressure (IOP) measurement method. A micro-optic-fiber pressure sensor was utilized for this purpose. Preliminary experiments with enucleated porcine eyes confirmed the sensor's accuracy in measuring both aqueous and vitreous humor pressure. The main study involved six healthy albino rabbits, where the sensor measured the pressure in the anterior chamber (aIOP) and posterior vitreous-cavity (pIOP). These measurements were compared to aIOP values obtained through rebound tonometry. Additionally, pre- and postoperative pressure comparisons were made after performing a vitrectomy. Results revealed a significant disparity between aqueous and vitreous humor pressures. Prior to vitrectomy, pIOP was 22.8 mmHg, over twice as high as aIOP (11.0 mmHg), but decreased to a similar level following the procedure. Comparison between the sensor measurements and rebound tonometry showed agreement in aIOP values. In conclusion, our study demonstrates that vitreous humor pressure is consistently higher than aqueous humor pressure, reaching the upper limit of normal IOP. Furthermore, vitrectomy effectively reduces pIOP, aligning it with aIOP. These findings contribute valuable insights into intraocular pressure dynamics and have implications for clinical interventions targeting ocular pressure regulation.

Evaluation of corneal hysteresis after pars plana vitrectomy combined phacoemulsification and intraocular lens implantation

We evaluated the early effects of pars plana vitrectomy (PPV) on corneal biomechanics by comparing corneal hysteresis (CH) after cataract surgery (phacoemulsification and aspiration with intraocular lens implantation; PEA + IOL) alone and PPV combined with cataract surgery. This study included 20 eyes (18 patients), who underwent cataract surgery alone (PEA + IOL group), and 28 eyes (27 patients) who underwent PPV combined with cataract surgery (PPV triple group). The CH was 11.1 ± 1.1, 10.4 ± 1.1, and 11.0 ± 1.0 mmHg in the PEA + IOL group and 11.0 ± 1.4, 9.8 ± 1.4, and 10.6 ± 1.6 mmHg in the PPV triple group, preoperatively, at 2 weeks, and 3 months after surgery, respectively. The CH was not significantly different after surgery in the PEA + IOL group, but decreased significantly in the PPV triple group 2 weeks following surgery (p < 0.01). Intraocular pressure (IOP) and central corneal thickness (CCT) did not change significantly after surgery in either group. Preoperatively, there was a positive correlation between CH and CCT in the PPV triple group, but the correlation disappeared postoperatively. In PPV combined with cataract surgery, CH temporarily decreased postoperatively, independent of IOP and CCT. Removal of the vitreous may reduce the elasticity and rigidity of the entire eye.