Effect of hyperosmotic agents on vitreous osmolality

Preoperative intravenous mannitol administration and its rationale before cataract surgery

BACKGROUND

The purpose of this study is to assess the variations in anterior chamber depth (ACD), axial length (AXL), and intraocular pressure (IOP) in both phakic and pseudophakic eyes undergoing preoperative intravenous mannitol infusion. The study was conducted at the Ophthalmology Department of IRCSS Humanitas in Milan, Italy. This is a prospective and non-randomized study.

METHODS

40 patients with phakic eyes and 40 patients with pseudophakic eyes scheduled for cataract surgery in their fellow eye were included. Prior to the surgery, comprehensive ophthalmic examinations were conducted, including IOP measurement, and bilateral biometry performed with Anterion® (Heidelberg Engineering GmbH, 69,115, Heidelberg, Germany). All patients received intravenous infusion of mannitol before the surgery. One hour after cataract extraction, the patients underwent the same set of examinations. We analyzed the changes AXL, ACD and IOP in the eye opposite to the one that underwent surgery.

RESULTS

The comparison between preoperative and postoperative parameters showed no differences in AXL (p = 0.34 and p = 0.53) and in ACD (p = 0.38 and p = 0.31) in the phakic and in the pseudophakic group, respectively. Instead, a statistically significant difference was found between the mean preoperative and postoperative IOP (p = 0.02) for the phakic group and (p = 0.03) for the pseudophakic group.

CONCLUSIONS

The administration of mannitol does not lead to any changes in the ACD and AXL, regardless of whether the eyes are phakic or pseudophakic. However, there is a statistically significant reduction in IOP. Nonetheless, it is important to consider the various side effects associated with mannitol infusion.

The effect of orally administered glycerol on anterior chamber depth during cataract surgery in eyes with narrow anterior chambers

PURPOSE

Cataract surgery on eyes with shallow anterior chambers may be demanding. Glycerol intake prior to surgery has been a well-known method in an effort to increase anterior chamber depth. It is used since it is thought that glycerol as an osmotic agent causes the vitreous body to shrink, pulling back the iris and thereby deepening the anterior chamber - making the surgery easier. Our controlled clinical trial tests this hypothesis and investigates the effect of glycerol on anterior chamber depth (ACD), intraocular pressure (IOP), corneal thickness (CCT), pupil diameter change after viscodilation (PD), operating time and perioperative complications.

METHODS

We performed a controlled clinical trial. All patients underwent cataract surgery on both eyes with at least 7 days apart. Preoperatively the patient was given glycerol orally when the right eye was operated - when the left eye was operated, nothing was given. In this way, each patient was serving as its own control. Measurements of ACD, IOP and CCT were performed before and after glycerol intake, pupillary diameter was measured before and after viscoelastics during the operation, and operating time and surgical complications were noted.

RESULTS

The study included 22 patients with bilateral cataract and anterior chambers depth <2.5 mm. Glycerol caused the anterior chamber to increase by 0.022 mm (p < 0.05), and IOP was lowered by 5.1 mmHg compared to the control group (p < 0.05). However, exposure to glycerol showed no effect on CCT, pupillary dilation of viscoelastics, operating time or surgical complications.

CONCLUSION

Glycerol increases anterior chamber depth and lowers intraocular pressure significantly. These changes had no significant impact on operating time nor on the complication rate, suggesting that these changes are too subtle to have a clinical impact on the cataract procedure.

Effects of oral isosorbide and glycerol on intraocular pressure, serum osmolality, and blood glucose in normal dogs

OBJECTIVE

To evaluate and compare the effects of oral isosorbide and glycerol on intraocular pressure (IOP), serum osmolality (SOSM), and blood glucose (BG) in normal dogs.

METHODS

  Ten normal dogs were administered an oral dose of either isosorbide (1.5 g/kg), glycerol (1.5g/kg) or control (water, 2 mL/kg) in a double blind protocol. Prior to dosing, baseline IOP, SOSM, and BG were measured in all dogs. IOP was subsequently evaluated every 30 min for 6h post-dosing. BG and SOSM were reassessed at times 1, 2, 4, and 6h post-dosing. After 1-week washout periods, every dog was subject to each of the three treatments. The dogs were held NPO for 4h after dosing.

RESULTS

  The maximal decrease in IOP was 17% by 1h and 13.5% by 30min after glycerol and isosorbide administration, respectively. However, the overall changes in IOP were not significant when compared to the controls. SOSM increased above baseline after dosing with glycerol but decreased after isosorbide, which difference was significant at 1, 2, and 4 h post-administration. BG significantly increased after administration of glycerol relative to the control but was not significantly affected by isosorbide.

CONCLUSIONS

  Neither glycerol nor isosorbide significantly affected IOP when compared to the control. However, glycerol induced significant elevations in both BG relative to the control and SOSM relative to isosorbide.

The effects of peroral glycerol on plasma osmolarity in diabetic patients and healthy individuals

Glycerol is used as a peroral treatment of increased intraocular and intracranial pressure due to its osmotic effect despite the potential increase in blood pressure and blood glucose. We examined the effects of peroral glycerol in diabetic patients and healthy individuals on blood pressure, capillary glucose, and plasma osmolarity. On two separate days, 15 diabetic patients ingested glycerol in doses of 855 and 1710 mg/kg body weight in a randomised, unmasked sequence. Five healthy individuals ingested a dose of 1710 mg/kg body weight. Mean arterial blood pressure (MAP), capillary glucose (CG) and plasma osmolarity (pOSM) were monitored for 180 min. At baseline, the MAP was comparable between the groups of healthy individuals and diabetic patients (p = 0.55), CG was marginal different (p = 0.06), and pOSM values were significantly different (p = 0.007). Following glycerol ingestion, a transient, non-significant increase occurred in blood pressure. Maximal DeltaCG was approximately 1 mM irrespective of the dose and presence of diabetes (p > 0.1). The pOSM response was analysed with a kinetic model and found independent of the presence of diabetes (p = 0.6). The maximal fitted DeltapOSM was 12.7 and 25.3 mOsm/l in the group of diabetic patients after the low and high dose, respectively, reflecting a dose-response relationship. Nausea, fatigue and headache were common side effects. In conclusion, peroral glycerol had similar effects on blood glucose, MAP and pOSM in the diabetic patients and healthy individuals. Specific precautions should not be implemented when treating diabetic patients with a single dose up to 1.7 g/kg body weight. A peak increase of 8% in the pOSM within 1 hr can be expected from this dose.

Magnetic resonance imaging studies of the volume of the rabbit eye with intravenous mannitol

PURPOSE

Changes in the volume of rabbit eyes after intravenous mannitol injection were studied non-invasively using 3D-magnetic resonance imaging (MRI).

METHODS

Images of eight rabbit eyes were obtained using a 3D-gradient echo technique before and at 30, 60 and 90 minutes after mannitol injection at 4 g/kg. To evaluate the volume, the cross-sectional area of the eye in the central 5 slices was traced and totaled. The intraocular pressure (IOP) of five rabbits was measured before and after administration.

RESULTS

The total area of the eyeball decreased significantly at 60 minutes. The total area of the anterior chamber, iris plus ciliary body decreased rapidly and then recovered. The decrease in the vitreous and the IOP was consistently significant during the 90-minute observation period.

CONCLUSIONS

Consecutive MRIs enabled us to measure the changes in eye volume of the same rabbit before and after mannitol injection in a non-invasive manner.

Increased aqueous flare as a result of a therapeutic dose of mannitol in humans

To evaluate the effects of mannitol on aqueous flare (aqueous protein concentration), we administered an intravenous clinical therapeutic dose to normal young adults (average age 20.1 years), to normal older adults (average age 61.5 years), and also to patients with diabetes mellitus, systemic hypertension, or pseudoexfoliation syndrome who were about to undergo intraocular surgery (average age 66.4 years). Protein and cell levels in the aqueous were determined with a device that measures laser light scatter in the aqueous. Mannitol increased the intensity of aqueous flare. In all subjects, the intensity of aqueous flare was greatest around 1 h following drug administration; the magnitude and duration of the aqueous flare increase were significantly greater in normal older adults than in normal young adults; the magnitude was essentially the same in older adults with and without disease. The effect reversed within 6 h of drug administration in normal subjects. We consider the findings to represent changes in actual aqueous protein concentration and discuss the possible causes of this phenomenon.