Clinical utilization of microperimetry in ophthalmic surgery: A narrative review

Microperimetry is an emerging technology that provides concurrent analysis of retinal structure and function by combining retinal sensitivity and fixation analysis with fundus imaging. We summarize the substantial evidence validating the evolving role of microperimetry as an adjunctive assessment of visual function in the perioperative setting. We show that microperimetry provides useful complementary information to other established imaging and functional modalities in the perioperative setting for a wide range of vitreoretinal surgical procedures, as well as in cataract and refractive surgeries. This includes preoperative uses such as prognostication of visual and anatomical outcomes, timing of surgical intervention, and assessment of patient suitability for surgery-as well as postoperative uses including quantification of visual recovery, investigation of unexplained postoperative vision loss, and informing expected long term functional outcomes.

Intraocular pressure fluctuation during resistance exercise

Objective

To evaluate the effect of weightlifting (leg press) on intraocular pressure (IOP).

Design

Prospective cohort study.

Subjects

A total of 24 participants met the inclusion criteria and completed the study procedures. Participants had an average age of 22.7±2.7 years and included nine women. The mean baseline IOP was 13.9 mm Hg (SD=2.4) with an average body mass index of 24.5 (SD= 3.1).

Methods

The maximum load for a single lift was found for each participant. Participants then performed three leg press regimens: one repetition using 95% of maximal load (1RM), six repetitions using 75% of maximal load (6RM) and isometric push against a weight much heavier than maximal load (ISO).

Main outcome measure

IOP was measured pre-exercise, during and immediately following the exercise using an iCare TA01i rebound tonometer. Blood pressure and HR were being monitored continuously during the lift. Optical coherence tomography images were obtained pre and postexercise session.

Results

The average maximum weight lifted by our participants was 331.9 Kg (SD=97.3). Transient increased IOP was observed across the 1RM, 6RM and ISO exercises with an average increase in 26.4 mm Hg (23.7 mm Hg to 28.7 mm Hg) to reach an average max IOP of 40.7 mm Hg (27.8 mm Hg to 54.2 mm Hg), with an absolute maximum of 70 mm Hg in one participant.

Conclusions

There is a transient and dramatic fluctuation in IOP with resistance training. This coupled with regular exposure to resistance training is potentially a significant risk factor for glaucoma. It should be noted that this study has been carried out in a healthy young population, and, thus, the external validity of these results in glaucoma participants requires further investigation.

Acute retinal ganglion cell injury caused by intraocular pressure spikes is mediated by endogenous extracellular ATP

Elevated intraocular pressure may lead to retinal ganglion cell injury and consequent visual deficits. Chronic intraocular pressure increase is a major risk factor for glaucoma, a leading blinding disease, and permanent visual deficits can also occur following acute pressure increments due to trauma, acute glaucoma or refractive surgery. How pressure affects retinal neurons is not firmly established. Mechanical damage at the optic nerve head, reduced blood supply, inflammation and cytotoxic factors have all been called into play. Reasoning that the analysis of retinal neurons soon after pressure elevation would provide useful cues, we imaged individual ganglion cells in isolated rat retinas before and after short hydrostatic pressure increments. We found that slowly rising pressure to peaks observed in trauma, acute glaucoma or refractive surgery (50-90 mmHg) did not damage ganglion cells, whereas a rapid 1 min pulse to 50 mmHg injured 30% of these cells within 1 h. The severity of damage and the number of affected cells increased with stronger or repeated insults. Degrading extracellular ATP or blocking the P2X receptors for ATP prevented acute pressure-induced damage in ganglion cells. Similar effects were observed in vivo. A short intraocular pressure transient increased extracellular ATP levels in the eye fluids and damaged ganglion cells within 1 h. Reducing extracellular ATP in the eye prevented damage to ganglion cells and accelerated recovery of their response to light. These data show that rapid pressure transients induce acute ganglion cell injury and unveil the causal role of extracellular ATP elevation in such injury.