Changes in intraocular pressure and ocular pulse amplitude of rhesus macaques after blue light scleral cross-linking

BACKGROUND

Scleral cross-linking can enhance the biomechanical strength of the sclera and is expected to be a new operative method for the prevention of myopia. However, studies investigating the changes in intraocular pressure (IOP) and ocular pulse amplitude (OPA) after blue light-riboflavin induced scleral collagen cross-linking (SXL) in rhesus monkeys are limited. This study aimed to investigate the changes in IOP and OPA in three-year-old rhesus macaques 1 week, 1 month, and 3 months after blue light-riboflavin SXL.

METHODS

Seven three-year-old rhesus macaques (14 eyes) were randomly divided into two groups, with 4 monkeys in group A (8 eyes) and 3 monkeys in group B (6 eyes). The right eye of each rhesus macaque was used as the experimental eye, whereas the left eye was used as the control. In group A, one quadrant of each right eye was irradiated. In group B, two quadrants of each right eye and one quadrant of each left eye were irradiated. The IOP and OPA of both eyes were measured in all seven rhesus macaques before SXL and 1 week, 1 month, and 3 months postoperatively, and differences in the IOP and OPA between the experimental and control eyes were evaluated via the paired t test.

RESULTS

In groups A and B, there were no significant differences between the experimental and control eyes in the IOP or OPA before SXL or 1 week, 1 month, or 3 months postoperatively (P > 0.05).

CONCLUSIONS

The IOP and OPA are not significantly affected in 1 vs 0 or in 1 vs 2 quadrants of blue light SXL.

[Intraocular pressure measurement inside the anterior chamber: a new technical solution and results]

AIM

To develop a new manometric device for intravital measurement of intraocular pressure (IOP) in the anterior chamber and to assess tonometric data reliability, including post-radial keratotomy (RK) measurements.

MATERIAL AND METHODS

The experiment was conducted in 2 isolated cadaver eyes, while the clinical study enrolled 20 patients (21 eyes) scheduled for cataract phacoemulsification surgery. Of them, 10 patients (10 eyes) with immature cataract and mild to moderate myopia constituted the control group. The study group consisted of the other 10 patients (11 eyes) with immature cataract, who had undergone RK more than 15 years earlier. The following tonometry methods were used: dynamic bi-directional corneal applanation (ORA, Reichert, USA), dynamic contour tonometry (Pascal tonometer, Zeimer, Switzerland), and rebound tonometry (ICare Pro, Tiolat, Finland). An original device was developed for intravital manometric measurements.

RESULTS

Manometric data obtained during the experiment matched the preset pressure in the anterior eye chamber. The median manometry results in the control and study groups were similar and equaled 21.5 and 21.0 mmHg, respectively. Preoperative tonometry readings ranged from 14.9 to 16.5 mmHg in the control group and from 19.7 to 23.3 mmHg - in the study group (with the exception of midperipheral rebound tonometry that showed 15.8 mmHg).

CONCLUSION

The developed device can well be used in experimental research. Midperipheral rebound tonometry was found to be the most informative method for post-RK IOP assessment. Manometry results in the study group mismatched tonometry readings in the controls, which might be due to the specifics of equipment calibration and requires further investigation.

System for Rapid, Precise Modulation of Intraocular Pressure, toward Minimally-Invasive In Vivo Measurement of Intracranial Pressure

Pathologic changes in intracranial pressure (ICP) are commonly observed in a variety of medical conditions, including traumatic brain injury, stroke, brain tumors, and glaucoma. However, current ICP measurement techniques are invasive, requiring a lumbar puncture or surgical insertion of a cannula into the cerebrospinal fluid (CSF)-filled ventricles of the brain. A potential alternative approach to ICP measurement leverages the unique anatomy of the central retinal vein, which is exposed to both intraocular pressure (IOP) and ICP as it travels inside the eye and through the optic nerve; manipulating IOP while observing changes in the natural pulsations of the central retinal vein could potentially provide an accurate, indirect measure of ICP. As a step toward implementing this technique, we describe the design, fabrication, and characterization of a system that is capable of manipulating IOP in vivo with <0.1 mmHg resolution and settling times less than 2 seconds. In vitro tests were carried out to characterize system performance. Then, as a proof of concept, we used the system to manipulate IOP in tree shrews (Tupaia belangeri) while video of the retinal vessels was recorded and the caliber of a selected vein was quantified. Modulating IOP using our system elicited a rapid change in the appearance of the retinal vein of interest: IOP was lowered from 10 to 3 mmHg, and retinal vein caliber sharply increased as IOP decreased from 7 to 5 mmHg. Another important feature of this technology is its capability to measure ocular compliance and outflow facility in vivo, as demonstrated in tree shrews. Collectively, these proof-of-concept demonstrations support the utility of this system to manipulate IOP for a variety of useful applications in ocular biomechanics, and provide a framework for further study of the mechanisms of retinal venous pulsation.