Evaluating tear clearance rate with optical coherence tomography

Nanostructured Lipid Carriers Mediated Drug Delivery to Posterior Segment of Eye and their In-vivo Successes

BACKGROUND

The disease of the posterior segment of the eye is a major concern worldwide, and it affects more than 300 million people and leads to serious visual deterioration. The current treatment available is invasive and leads to serious eye complications. These shortcomings and patient discomfort lead to poor patient compliance. In the last decade, Nanostructured lipid carriers (NLC) have established a remarkable milestone in the delivery of drug substances to the posterior segment of the eye. Additionally, NLC can reduce the clearance due to adhesive properties which are imparted due to nano-metric size. This attribute might reduce the adverse effects associated with intravitreal therapy and thus enhance therapeutic efficacy, eventually raising patient adherence to therapy. The current review provides an inclusive account of NLC as a carrier to target diseases of the posterior segment of the eye.

OBJECTIVE

The review focuses on the various barrier encountered in the delivery of drugs to the posterior segment of the eye and the detail about the physicochemical property of drug substances that are considered to be suitable candidates for encapsulation to lipid carriers. Therefore, a plethora of literature has been included in this review. The review is an attempt to describe methods adopted for assessing the in-vivo behavior that strengthens the potential of NLC to treat the disease of the posterior segment of the eye.

CONCLUSION

These NLC-based systems have proven to be a promising alternative in place of invasive intravitreal injections with improved patient compliance.

Eliciting blinks by transcutaneous electric nerve stimulation improves tear fluid in healthy video display terminal users: A self-controlled study

We aimed to elicit strong blinks among healthy video display terminal (VDT) users by periorbital transcutaneous electric nerve stimulation (TENS) and evaluate its impact on the tear fluid and visual task. Appropriate TENS conditions were evaluated to evoke strong blinks under minimum discomfort. Seventeen healthy VDT users with noninvasive Keratograph first breakup time (NIKf-BUT) 5-15 s and Ocular Surface Disease Index (OSDI) scores < 15 were recruited in this study. Before the trial, noninvasive Keratograph average breakup time (NIKa-BUT), tear meniscus height (TMH) and OSDI scores were evaluated. Before each TENS session, the volunteers played Tetris while the corresponding blink rate and Tetris scores were recorded. Then, the participants underwent 30 minutes of TENS, which evoked blinking of their right eye 20 times per minute. Tetris scores were evaluated again during TENS. The Tetris scores and corresponding blink rate were assessed after each TENS session while NIKa-BUT, TMH and OSDI scores were recorded after the third and sixth TENS sessions. We found that OSDI scores declined significantly after the sixth TENS (P = .003). The NIKa-BUT of the right eye was promoted after the sixth TENS (P = .02), and the TMH was higher after the third and sixth TENS in both eyes (P = .03, P = .03 for right eyes respectively, P = .01, P = .01 for left eyes respectively). There was no significant difference between the adjusted Tetris scores before and during TENS (P = .12). The blink rate before and after TENS were unaffected after 6 sessions (P = .61). The results indicated that periorbital TENS effectively ameliorated ocular irritation and improved tear secretion and tear film stability by eliciting strong blinks in healthy VDT users without disturbing the visual task.

Influence of Sodium Hyaluronate Concentration in Tear Meniscus Height: 10-min Dynamic Profile After Single Instillation

PURPOSE

To assess the height, area, and density of tear meniscus throughout 10 min after instillation of sodium hyaluronate (SH) of equal molecular weight at two different concentrations.

METHODS

Thirty-four eyes from 17 patients were enrolled in this longitudinal, nonrandomized, interventional and contralateral eye study. Tear meniscus height (TMH), corneal meniscus junction (CMJ), lower-lid meniscus junction (LLMJ), and tear meniscus area (TMA) images were obtained with the anterior segment module of the deep range imaging ocular coherence tomography ([DRI-OCT] Triton Swept-Source). Tear meniscus density (TMD) was calculated using the image processing and analysis software by Java (ImageJ program). Sodium hyaluronate artificial tears at 0.1% and 0.2% concentrations were instilled into all right and left eyes, respectively.

RESULTS

Patients' mean age was 61.05±11.43 years. Tear meniscus height, CMJ, LLMJ, and TMA measured at 1-, 5-, 7- and 10-min postinstillation of 0.1% SH proved significant differences among them (P<0.05). Sodium hyaluronate 0.2% instillation obtained similar findings, although no significant differences were found between 1- and 3-min postinstillation measurements (P>0.05). Fewer differences were found in TMD 0.2% SH group due to a lower baseline densitometry compared to the 0.1% group.

CONCLUSION

0.2% sodium hyaluronate achieved better TMH and TMA in 1 and 3 min after instillation than 0.1% concentration. However, there were no statistically significant differences between 0.1% and 0.2% sodium hyaluronate throughout a ten-minute longitudinal profile measurement using DRI-OCT.

Cutting-edge advances in therapy for the posterior segment of the eye: Solid lipid nanoparticles and nanostructured lipid carriers

Posterior segment eye diseases affect more than 300 million patients worldwide resulting in severe visual impairment. The treatments available are invasive, costly, present irregular effectiveness, and cause serious adverse effects. These drawbacks significantly reduce patient compliance. In the last decade, solid lipid nanoparticle (SLN) and nanostructured lipid carrier (NLC) have shown potential as innovative carriers for lipophilic drug substances to overcome hurdles in treating the eye posterior segment. This review shows the advantages of these formulations, focusing on their compatibility with ocular tissues, which increases the internalization of the drug substances. Additionally, SLN and NLC can reduce the clearance by the eye's protective mechanisms due to adhesive properties related to nanometric size. Therefore, these preparations may allow the treating of several ophthalmic diseases by topical administration, increasing the interval between doses. This feature can decrease adverse effects and enhance efficacy, ultimately improving patient compliance. Thus, this critical review presents the performance of the in vitro, ex vivo, and in vivo assays that support the potential of SLN and NLC to treat diseases of the posterior segment of the eye. These nanoparticles have shown to be promising alternative towards a major shift in developing ophthalmic products.

Fourier-Domain OCT Imaging of the Ocular Surface and Tear Film Dynamics: A Review of the State of the Art and an Integrative Model of the Tear Behavior During the Inter-Blink Period and Visual Fixation

In the last few decades, the ocular surface and the tear film have been noninvasively investigated in vivo, in a three-dimensional, high resolution, and real-time mode, by optical coherence tomography (OCT). Recently, OCT technology has made great strides in improving the acquisition speed and image resolution, thus increasing its impact in daily clinical practice and in the research setting. All these results have been achieved because of a transition from traditional time-domain (TD) to Fourier-domain (FD) technology. FD-OCT devices include a spectrometer in the receiver that analyzes the spectrum of reflected light on the retina or ocular surface and transforms it into information about the depth of the structures according to the Fourier principle. In this review, we summarize and provide the state-of-the-art in FD-OCT imaging of the ocular surface system, addressing specific aspects such as tear film dynamics and epithelial changes under physiologic and pathologic conditions. A theory on the dynamic nature of the tear film has been developed to explain the variations within the individual compartments. Moreover, an integrative model of tear film behavior during the inter-blink period and visual fixation is proposed.

Evaluation of the tear clearance rate by dacryoscintigraphy in patients with obstructive meibomian gland dysfunction

PURPOSE

To measure tear clearance values in patients with meibomian gland dysfunction (MGD) with a dynamic nuclear medicine method, namely, dacryoscintigraphy (DSCI).

METHODS

Twenty-four MGD patients and 24 healthy volunteers were examined. During DSCI one drop of a solution with 100 MBq/mL^99mTc sodium pertechnetate was instilled with a micropipette into the lacrimal lake of both eyes. Measurements were performed according to a dynamic data acquisition protocol, which resulted in summed DSCI images. Data were also evaluated separately in special regions of interest (ROI), and consecutive time activity curves were created. Tear clearance (T½) values were calculated based on the activity curves. In addition, tear osmolarity measurements, tear breakup time (tBUT), and Schirmer I (ST_I) tests were performed prior to DSCI examination.

RESULTS

The T½ values were 29.91 ± 11.61 min in MGD patients and 6.26 ± 1.5 min in healthy controls. Tear osmolarity parameters were 308 ± 9.41 mOsm/L and 288.9 ± 6.4 mOsm/L, tBUT values were 5.54 ± 2.73 s and 11.4 ± 2.7 s, while the ST_I test values were 6.17 ± 2.78 mm and 13.58 ± 3.8 mm, respectively. The differences were significant (p < 0.01) in all cases.

CONCLUSIONS

Although the MGD patients' lacrimal drainage systems were patent their tear clearance values were significantly higher than those of healthy volunteers, which may be caused by decreased drainage of tears from the eyes towards the nasal cavity. The understanding of new features regarding the altered physico-chemical characteristics of MGD tears has been augmented by the results of this study.