Ocular residence time of carboxymethylcellulose solutions

Physicochemical Properties of Hyaluronic Acid-Based Lubricant Eye Drops

PURPOSE

To assess the physicochemical properties of hyaluronic acid (HA)-based artificial tears.

METHODS

The average molecular weight (MW) and polydispersion index (PDI) of HA in 18 commercially available artificial tears were determined by light scattering/high-performance liquid chromatography. Osmolality, pH, viscosity, and sodium concentration were determined using an osmometer, pH meter, rheometer, and inductively coupled plasma mass spectrometer, respectively.

RESULTS

The MW of HA varied considerably between formulations. The PDI was >2.0 in two formulations (2.28 and 4.94), suggesting the presence of a copolymer and/or HA size variability. Three formulations exhibited viscosity exceeding the blur threshold at different shear rates. Viscosity at low shear rates was generally highest in formulations containing high-MW HA. Correlations were found between observed viscosity and a predictive/calculated value, except for four copolymer-containing formulations, and osmolality (range, 154-335 mOsm/kg) and sodium concentration (range, 22-183 mM), with two exceptions. Compared with organic osmolytes, adding sodium decreased viscosity, particularly at lower shear rates.

CONCLUSIONS

In the context of the literature, our findings suggest that for most patients with dry eye disease, the ideal HA-based artificial tear should include high-MW HA with a low PDI and exhibit enhanced viscosity at low shear rate (without exceeding the blur threshold). The inclusion of synergistic copolymers and a low sodium concentration may increase viscosity, but whether any of these physicochemical properties or correlations can predict clinical efficacy will require further investigation.

TRANSLATIONAL RELEVANCE

Understanding the properties of HA-based artificial tears will support the development of unique formulations that target specific ocular surface conditions.

Comparison of ketorolac 0.45% versus diclofenac 0.1% for macular thickness and volume after uncomplicated cataract surgery

PURPOSE

To compare the effects of ketorolac 0.45% and diclofenac 0.1% on macular thickness and volume after uncomplicated cataract surgery.

METHODS

A total of 76 eyes of 76 patients who underwent uncomplicated cataract surgery were included. Patients were treated with either diclofenac 0.1% (38 eyes) or ketorolac 0.45% (38 eyes) after surgery. The macular thickness and volume were obtained with optical coherence tomography (OCT). Central subfield thickness (CST, OCT 1 mm zone), total foveal thickness (TFT, OCT 3 mm zone), total macular thickness (TMT, OCT 6 mm zone), average macular thickness (AMT) and total macular volume (TMV) were compared between the two study groups.

RESULTS

No significant differences between groups were found in macular thickness or volume 1 month after cataract surgery. Two months after surgery, the ketorolac group had significantly lower CST, TFT, TMT and AMT than the diclofenac group (p < 0.05 for all). Additionally, 1 and 2 months after surgery, changes from preoperative values in CST (both p = 0.04), AMT (p = 0.02 and p < 0.01, respectively) and TMV (both p = 0.04) were significantly less in the ketorolac group than in the diclofenac group.

CONCLUSIONS

Following uncomplicated cataract surgery, topical ketorolac 0.45% was more effective than diclofenac 0.1% in preventing increases in macular thickness and volume.

Ocular penetration and anti-inflammatory activity of ketorolac 0.45% and bromfenac 0.09% against lipopolysaccharide-induced inflammation

PURPOSE

Anti-inflammatory activity of topical nonsteroidal anti-inflammatory drugs is mediated by suppression of cyclooxygenase (COX) isoenzymes. This study compared ocular penetration and inflammation suppression of topical ketorolac 0.45% and bromfenac 0.09% ophthalmic solutions in a rabbit model.

METHODS

At hour 0, 36 rabbits received ketorolac 0.45%, bromfenac 0.09%, or an artificial tear 3 times once every 20 min. Half of the rabbits in each group then received intravenous injections of lipopolysaccharide (LPS) and fluorescein isothiocyanate (FITC)-dextran at hour 1, and the other half at hour 10. Aqueous and iris-ciliary body (ICB) samples were collected in the former group at hour 2 (peak) and in the latter group at hour 11 (trough) An additional group of 6 animals received only FITC-dextran, and samples were collected 1 h later. Peak and trough nonsteroidal anti-inflammatory drug concentrations were compared with previously determined half-maximal inhibitory concentrations (IC(50)) for COX isoenzymes.

RESULTS

Peak and trough aqueous and ICB concentrations of ketorolac were at least 7-fold or greater than those of bromfenac. At peak levels, both ketorolac 0.45% and bromfenac 0.09% significantly inhibited LPS-induced aqueous prostaglandin E(2) and FITC-dextran elevation (P < 0.01). At trough, both study drugs significantly inhibited LPS-induced aqueous prostaglandin E(2) elevation (P < 0.05), but only ketorolac 0.45% significantly reduced LPS-induced aqueous FITC-dextran elevation (P < 0.01). Aqueous and ICB ketorolac concentrations exceeded its IC(50) for COX-1 and COX-2 at peak and trough. Aqueous and ICB bromfenac levels exceeded its IC(50) for COX-2 at peak and trough, but not for COX-1 at trough aqueous levels and peak and trough ICB levels.

CONCLUSIONS

Both ketorolac 0.45% and bromfenac 0.09% effectively suppressed inflammation at peak. At trough, only ketorolac 0.45% effectively suppressed inflammation as measured by FITC-dextran leakage. The difference in inflammation suppression may be due to differences in tissue concentrations and/or greater COX-1 suppression by ketorolac 0.45%.

Ocular pharmacokinetics of 0.45% ketorolac tromethamine

Purpose

A new carboxymethylcellulose (CMC)-containing ophthalmic formulation of 0.45% ketorolac, pH 6.8 (Acuvail^®) was recently developed for treatment of inflammation and pain after cataract surgery. This study compared pharmacokinetics of the new formulation with that of a prior formulation, 0.4% ketorolac, pH 7.4 (Acular LS^®).

Methods

Ketorolac formulations were administered bilaterally (35 μL) to female New Zealand White rabbits. Samples from aqueous humor and iris-ciliary body were collected at multiple time points, and ketorolac was quantified using liquid chromatography-tandem mass spectrometry.

Results

In aqueous humor, the peak concentration (C_max) and area under the concentration-time curve (AUC_0–τ) of ketorolac were, respectively, 389 ng/mL and 939 ng·h/mL following administration of the CMC-containing 0.45% ketorolac, pH 6.8, and 211 ng/mL and 465 ng·hr/mL following administration of the 0.4% ketorolac, pH 7.4. In iris-ciliary body, C_max and AUC_0–τ of ketorolac were, respectively 450 ng/g and 2040 ng·h/g after administration of the CMC-containing 0.45% ketorolac, pH 6.8, and 216 ng/g and 699 ng·h/g after administration of the 0.4% ketorolac, pH 7.4. PK simulations predicted an AUC_0–τ of 2910 ng·h/g for twice daily, CMC-containing 0.45% ketorolac, pH 6.8, compared to 725 ng·h/g for 4 times daily, 0.4% ketorolac, pH 7.4.

Conclusions

The CMC-containing formulation of 0.45% ketorolac, pH 6.8, increased ketorolac bioavailability by 2-fold in aqueous humor and by 3-fold in iris-ciliary body in comparison to the 0.4% ketorolac, pH 7.4, allowing a reduced dosing schedule from 4 times daily to twice daily.

Effect of viscosity on tear drainage and ocular residence time

PURPOSE

An increase in residence time of dry eye medications including artificial tears will likely enhance therapeutic benefits. The drainage rates and the residence time of eye drops depend on the viscosity of the instilled fluids. However, a quantitative understanding of the dependence of drainage rates and the residence time on viscosity is lacking. The current study aims to develop a mathematical model for the drainage of Newtonian fluids and also for power-law non-Newtonian fluids of different viscosities.

METHODS

This study is an extension of our previous study on the mathematical model of tear drainage. The tear drainage model is modified to describe the drainage of Newtonian fluids with viscosities higher than the tear viscosity and power-law non-Newtonian fluids with rheological parameters obtained from fitting experimental data in literature. The drainage rate through canaliculi was derived from the modified drainage model and was incorporated into a tear mass balance to calculate the transients of total solute quantity in ocular fluids and the bioavailability of instilled drugs.

RESULTS

For Newtonian fluids, increasing the viscosity does not affect the drainage rate unless the viscosity exceeds a critical value of about 4.4 cp. The viscosity has a maximum impact on drainage rate around a value of about 100 cp. The trends are similar for shear thinning power law fluids. The transients of total solute quantity, and the residence time agrees at least qualitatively with experimental studies.

CONCLUSIONS

A mathematical model has been developed for the drainage of Newtonian fluids and power-law fluids through canaliculi. The model can quantitatively explain different experimental observations on the effect of viscosity on the residence of instilled fluids on the ocular surface. The current study is helpful for understanding the mechanism of fluid drainage from the ocular surface and for improving the design of dry eye treatments.

Effect of an oil-in-water emulsion on the tear physiology of patients with mild to moderate dry eye

PURPOSE

To determine the effect of an oil-in-water emulsion eye drop compared with a conventional dry eye supplement (hypromellose) on tear physiology in dry eye.

METHODS

A randomized parallel, longitudinal, and investigator-masked study of the efficacy of 1.25% castor oil emulsion and 0.32% hypromellose solution was carried out. A total of 53 patients with mild to moderate dry eye (27 in emulsion group and 26 in hypromellose group) were recruited for the study. Patients were enrolled if they reported at least 2 symptoms on a McMonnies Dry Eye Questionnaire together with 1 of the following screening tests: noninvasive tear breakup time (5-10 seconds) and Schirmer test without anesthesia (2-5 mm in 5 minutes). Patients were instructed to use the test solutions 3 times a day for 30 days. Tear production, evaporation, lipid layer structure, and osmolality were measured before and 30 days after use of the drops.

RESULTS

A statistically significant decrease was seen after 1 month in tear evaporation rates with both emulsion (7.25 +/- 5.43 g/m2/h) and hypromellose (2.02 +/- 4.75 g/m2/h). However, the decrease with emulsion was significantly greater than with hypromellose (P < 0.001). Lipid layer structure improved from day 1 to day 30 of the study with the emulsion but not with the hypermellose. No significant changes were seen in tear production and osmolality with either of the drops.

CONCLUSIONS

The oil-water emulsion was more effective in reducing tear evaporation than hypromellose after repeated application over a 1-month period. This finding signifies the potential of the emulsion in the management of evaporative dry eye.

Investigation of Corneal Effect of Different Types of Artificial Tears in a Simulated Dry Eye Condition Using a Novel Porcine Dry Eye Model (pDEM)

PURPOSE

To use a novel porcine dry eye model (pDEM) to study the effect of various artificial tears on corneal abrasion and epithelial cell death under severe "dry eye" conditions.

METHODS

A 60-second lacrimation-blink interval, which simulates a severe dry eye condition, was set up with our novel pDEM. The corneal protective effect of lubricating the eye for 4 hours with Dulbecco phosphate-buffered saline (DPBS, as control; n = 20) and with 3 types of commercially available artificial tears (n = 17 for each) that contained different lubricating agents was studied. Effect was determined in terms of the change in fluorescein staining grade (on a 0-4 point scale with 0.5 increments) of the cornea and the number of dead cells (by trypan blue staining) on the corneal surface.

RESULTS

Median increase in fluorescein grading (median) in corneas treated for 4 hours with artificial tears containing sodium hyaluronate or hydroxypropyl methylcellulose was significantly (P < 0.002) smaller than with artificial tears containing balanced saline with an unknown demulcent or the DPBS control. The numbers of dead epithelial cells in the central corneas lubricated with artificial tears containing sodium hyaluronate or hydroxypropyl methylcellulose (229 +/- 71 and 221 +/- 65 [SD], respectively) were also significantly (P < 0.005) smaller than those in the corneas of eyes lubricated with artificial tears containing balanced saline with an unknown demulcent or DPBS alone (328 +/- 106 and 341 +/- 113, respectively).

CONCLUSION

Results show that artificial tears containing sodium hyaluronate or hydroxypropyl methylcellulose as lubricating agents give enhanced corneal protection against desiccation and show the use of this novel pDEM model in evaluating corneal protection from desiccation.

Management of filamentary keratitis associated with aqueous-deficient dry eye

PURPOSE

To review the incidence, underlying pathophysiology, and clinical features of filamentary keratitis and to identify evidence-based best-practice strategies for managing filamentary keratitis.

METHODS

A comprehensive review of published literature was undertaken. Recommendations for best-practice management strategies were based on the available evidence. Three cases are presented to illustrate the clinical findings and management of patients with chronic filamentary keratitis.

RESULTS

Although the evidence base is limited by the absence of well-designed studies, current evidence indicates the following: (1) Aqueous-deficient dry eye (keratoconjunctivitis sicca) is the most common ocular condition associated with filamentary keratitis. (2) Current best-practice management of filamentary keratitis involves treating the underlying dry eye and specific treatments for the corneal filaments. Proposed treatments include nonpreserved lubricants, topical steroidal and nonsteroidal anti-inflammatory agents, and punctal plugs for aqueous-deficient dry eye as well as mechanical removal of filaments, hypertonic saline, mucolytic agents, and bandage contact lenses for the filaments. (3) Filamentary keratitis can be induced or exacerbated by contact lens wear and ocular surgical procedures such as cataract surgery and corneal graft surgery. Pre- and postoperative ocular surface management strategies should be considered in the surgical planning of patients with, or who are susceptible to, filamentary keratitis. Filamentary keratitis can also be induced and/or exacerbated by chronic use of ocular and/or systemic medications, and alternate medications or additional measures to manage the tear film and ocular surface may be required in these cases.

CONCLUSIONS

Filamentary keratitis can be a chronic, recurrent, and debilitating condition. With a systemic approach to diagnosis and management, the condition can be effectively controlled and the incidence and severity of recurrences minimized.

Coefficient of Friction of Ocular Surface Lubricants for Laser in situ Keratomileusis

PURPOSE

The coefficient of friction was empirically derived for a series of commercially available ophthalmic lubricants having potential use during laser in situ keratomileusis (LASIK).

METHODS

Measurements were obtained using a modified tensile testing machine. Solutions tested included the artificial tear supplements Polytears-free, Bion Tears, Genteal, Refresh, Cellufresh, Celluvisc, Theratears, and Viscotears gel; and balanced salt solution (BSS).

RESULTS

Viscotears carbomer gel had a significantly lower mean coefficient of friction compared to other ophthalmic lubricants tested (P=.002) and the dry plate (P=.005). Addition of 0.1 ml of BSS to 0.025 ml of Celluvisc significantly reduced the coefficent of friction of Celluvisc (P=.01). Polytears, Bion Tears, Genteal, Refresh, Celluvisc, Theratears, and BSS had coefficients of friction significantly higher than that of the dry plate.

CONCLUSION

A range of values were obtained for the coefficient of the ophthalmic lubricants tested. Viscotears gel (0.1 ml), and Celluvisc (0.025 ml) + BSS (0.1 ml) had coefficients of friction significantly lower than that of the dry plate.