The Tear Film and the optical Quality of the Eye

Ocular Surface Fluid: More than a Matrix

Although the eye can be subjected to therapeutic manipulation, some of its structures are highly inaccessible. Thus, conventional therapeutic administration pathways, such as topical or systemic routes, usually show significant limitations in the form of low ocular penetration or the appearance of side effects linked to physiology, among others. The critical feature of many xenobiotics is the drug gradient from the concentrated tear reservoir to the relatively barren corneal and conjunctival epithelia, which forces a passive route of absorption. The same is true in the opposite direction, towards the ocular surface (OS). With the premise that tears can be regarded as equivalent to or a substitute for plasma, researchers may determine drug concentrations in the OS fluid. Within this framework, a survey of scholarly sources on the topic was conducted. It provided an overview of current knowledge, allowing the identification of relevant theories, methods, and gaps in the existing research that can be employed in subsequent research. OS fluid (tears particularly) has enormous potential as a source of biological material for external drug screening and as a biomarker of various systemic diseases. Given the numerous alternate matrices, knowledge of their properties is very important in selecting the most appropriate specimens in toxicological analyses.

Influence of perfluorohexyloctane (Evotears®) on higher order aberrations

PURPOSE

To prospectively assess the effect of regular application of perfluorohexyloctane (F6H8; Evotears®) on the tear film lipid layer, higher order aberrations (HOA) and the repeatability of measurements in healthy eyes.

METHODS

This prospective clinical study included 104 eyes treated with F6H8 four times daily for four weeks (group A) and 101 eyes that served as controls (group B). Measurements were performed with the WASCA aberrometer (Carl Zeiss Meditec GmbH, Jena, Germany). Main outcome measurement in addition to subjective refraction were the root mean square values of HOA measured before and after the intervention.

RESULTS

Regular use of F6H8 over a period of four weeks significantly increases HOA in healthy eyes (p < 0.05). In addition, the repeatability of measurement increases after the application of F6H8.

CONCLUSION

F6H8 may be a suitable treatment option to improve the accuracy of refractive assessment, although it increases HOA. Further studies are needed to confirm the effect on HOA and the repeatability of measurement.

Aquaporin 5 in the eye: Expression, function, and roles in ocular diseases

As a water channel protein, aquaporin 5 (AQP5) is essential for the maintenance of the normal physiological functions of ocular tissues. This review provides an overview of the expression and function of AQP5 in the eye and discusses their role in related eye diseases. Although AQP5 plays a vital role in ocular functions, such as maintaining corneal and lens transparency, regulating water movement, and maintaining homeostasis, some of its functions in ocular tissues are still unclear. Based on the key role of AQP5 in eye function, this review suggests that in the future, eye diseases may be treated by regulating the expression of aquaporin.

Exploring the Cutting Edge of Vision Science: New Developments in Diagnostics and Treatment of Ocular Surface in Dry Eye Disease

The ocular surface refers to the outermost layer of the eye, which includes the cornea, conjunctiva and eyelids [...].

Hyperglycemia Induces Tear Reduction and Dry Eye in Diabetic Mice through the Norepinephrine-α1 Adrenergic Receptor-Mitochondrial Impairment Axis of Lacrimal Gland

Dry eye syndrome is a common complication in diabetic patients with a prevalence of up to 54.3%. However, the pathogenic mechanisms underlying hyperglycemia-induced tear reduction and dry eye remain less understood. The present study indicated that both norepinephrine (NE) and tyrosine hydroxylase levels were elevated in the lacrimal gland of diabetic mice, accompanied by increased Fos proto-oncogene (c-FOS)+ cells in the superior cervical ganglion. However, the elimination of NE accumulation by surgical and chemical sympathectomy significantly ameliorated the reduction in tear production, suppressed abnormal inflammation of the lacrimal gland, and improved the severity of dry eye symptoms in diabetic mice. Among various adrenergic receptors (ARs), the α1 subtype played a predominant role in the regulation of tear production, as treatments of α1AR antagonists improved tear secretion in diabetic mice compared with βAR antagonist propranolol. Moreover, the α1AR antagonist alfuzosin treatment also alleviated functional impairments of the meibomian gland and goblet cells in diabetic mice. Mechanically, the α1AR antagonist rescued the mitochondrial bioenergetic deficit, increased the mitochondrial DNA copy numbers, and elevated the glutathione levels of the diabetic lacrimal gland. Overall, these results deciphered a previously unrecognized involvement of the NE-α1AR-mitochondrial bioenergetics axis in the regulation of tear production in the lacrimal gland, which may provide a potential strategy to counteract diabetic dry eye by interfering with the α1AR activity.

Targeting purinergic receptors to attenuate inflammation of dry eye

Inflammation is one of the potential factors to cause the damage of ocular surface in dry eye disease (DED). Increasing evidence indicated that purinergic A₁, A_2A, A₃, P2X4, P2X7, P2Y₁, P2Y₂, and P2Y₄ receptors play an important role in the regulation of inflammation in DED: A₁ adenosine receptor (A_1R) is a systemic pro-inflammatory factor; A_2AR is involved in the activation of the MAPK/NF-kB pathway; A_3R combined with inhibition of adenylate cyclase and regulation of the mitogen-activated protein kinase (MAPK) pathway leads to regulation of transcription; P2X4 promotes receptor-associated activation of pro-inflammatory cytokines and inflammatory vesicles; P2X7 promotes inflammasome activation and release of pro-inflammatory cytokines IL-1β and IL-18; P2Y receptors affect the phospholipase C(PLC)/IP3/Ca²⁺ signaling pathway and mucin secretion. These suggested that purinergic receptors would be promising targets to control the inflammation of DED in the future.

The influence of a mineral oil cationic nanoemulsion or perfluorohexyloctane on the tear film lipid layer and higher order aberrations

PURPOSE

To prospectively assess the effect of a single and regular application of either a cationic nanoemulsion of mineral oil (CN) or perfluorohexyloctane (F6H8) on the lipid layer of the tear film and higher order aberrations (HOA) in patients with Dry Eye Disease (DED).

METHODS

Fifty-seven patients with a lipid layer thickness (LLT) ≤ 75 interferometric colour units (ICU) were included in the study. In group A (20 patients) the effect of a single drop of F6H8 or CN on HOA and LLT was assessed immediately after application and up to two hours later. For long term effects (Group B) 37 patients applied CN or F6H8 five times a day for 12 weeks. Measurement of LLT, HOA, non-invasive-tear-break-up-time (NIBUT) and meibography were assessed prior to as well as at 4 weeks and 12 weeks after initiation of treatment. Our study is registered in the "German Clinical Trials Register" under the trial number: DRKS00028696.

RESULTS

CN led to an increase of the LLT from 46.8 ± 16.9 ICU to 76.3 ± 23.5 ICU (p = 0.021) and to an increase of HOA from 0.43 ± 0.06 μm to 0.48 ± 0.08 μm immediately after application (p = 0.027). There was no correlation between the increase of LLT and HOA (r = -0.04; p = 0.90). In group B an increase of LLT was observed in the F6H8 group from 45.8 ± 8.8 ICU at baseline to 66.7 ± 19.5 ICU at 12 weeks (p = 0.002). No changes of HOA were measured throughout the observation period in group B. After 12 weeks CN increased NIBUT from 9.9 ± 5.3 seconds to 15.5 ± 5.6 seconds (p = 0.04). F6H8 increased NIBUT from 12.4 ± 5.9 seconds to 16.9 ± 4.7 seconds (p = 0.02) after 12 weeks.

CONCLUSION

CN leads to a short-term increase in LLT and HOA, but only immediately after application. In contrast F6H8 does lead to an increase of LLT after regular long-term use but has no effect on HOA. The regular application of lipid-based products does not seem to decrease the quality of vision as measured in HOA. Instead, CN and F6H8, both are able to stabilize the tear film after regular application.

Assessment of the Effect of Wearing a Surgical Face Mask on Tear Film in Normal Eye Subjects

Purpose. To assess the effect of wearing a face mask for a short time on the tear film parameters in normal eye subjects. Methods. Fifty-four normal eye subjects (14 female and 40 male) aged 18–40 years (23.8 ± 4.4 years) were recruited. A standardized patient evaluation of eye dryness was completed first, followed by noninvasive tear break-up time, phenol red thread, and tear ferning tests. A 5-minute gap was allowed between the tests. The subjects were asked to wear a surgical mask for one hour. The measurements were taken both before wearing a face mask and immediately after its removal. Results. Significant (Wilcoxon test) differences were found between the standardized patient evaluation of eye dryness ( $p=0.002$ ) and the noninvasive tear break-up time scores ( $p<0.001$ ) before and after wearing face masks. No significant differences (Wilcoxon test, $p>0.05$ ) were found between the phenol red thread scores and tear ferning grades before and after wearing face masks. Strong correlations (Spearman’s rank correlation coefficient, r) were found among the standardized patient evaluation of eye dryness score (r = 0.590; $p<0.001$ ), noninvasive tear break-up time measurements (r = 0.631; $p<0.001$ ), and the tear ferning grades (r = 0.517; $p<0.001$ ) before and after wearing the mask. A medium correlation (r = 0.377; $p=0.005$ ) was found between the noninvasive tear break-up time scores and tear ferning grades before wearing the mask. Conclusions. Wearing a surgical face mask for a short duration of one hour has an effect on ocular tear film in normal eye subjects. Dry eye symptoms and tear break-up increased after wearing a face mask compared with those experienced before wearing one.

Predicting subjective refraction with dynamic retinal image quality analysis

The aim of this work is to evaluate the performance of a novel algorithm that combines dynamic wavefront aberrometry data and descriptors of the retinal image quality from objective autorefractor measurements to predict subjective refraction. We conducted a retrospective study of the prediction accuracy and precision of the novel algorithm compared to standard search-based retinal image quality optimization algorithms. Dynamic measurements from 34 adult patients were taken with a handheld wavefront autorefractor and static data was obtained with a high-end desktop wavefront aberrometer. The search-based algorithms did not significantly improve the results of the desktop system, while the dynamic approach was able to simultaneously reduce the standard deviation (up to a 15% for reduction of spherical equivalent power) and the mean bias error of the predictions (up to 80% reduction of spherical equivalent power) for the handheld aberrometer. These results suggest that dynamic retinal image analysis can substantially improve the accuracy and precision of the portable wavefront autorefractor relative to subjective refraction.

Human ocular mucins: The endowed guardians of sight

Mucins are an ancient group of glycoproteins that provide viscoelastic, lubricating and hydration properties to fluids bathing wet surfaced epithelia. They are involved in the protection of underlying tissues by forming a barrier with selective permeability properties. The expression, processing and spatial distribution of mucins are often determined by organ-specific requirements that in the eye involve protecting against environmental insult while allowing the passage of light. The human ocular surface epithelia have evolved to produce an extremely thin and watery tear film containing a distinct soluble mucin product secreted by goblet cells outside the visual axis. The adaptation to the ocular environment is notably evidenced by the significant contribution of transmembrane mucins to the tear film, where they can occupy up to one-quarter of its total thickness. This article reviews the tissue-specific properties of human ocular mucins, methods of isolation and detection, and current approaches to model mucin systems recapitulating the human ocular surface mucosa. This knowledge forms the fundamental basis to develop applications with a promising biological and clinical impact.

REPEATABILITY OF MACULAR MICROVASCULATURE MEASUREMENTS USING OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY ACCORDING TO TEAR BREAKUP TIME IN DRY EYE DISEASE

PURPOSE

It is hypothesized that an unstable tear film would affect the quality and repeatability of optical coherence tomography angiography (OCTA). Therefore, OCTA repeatability according to tear break-up time (TBUT) was compared.

METHODS

The 3 × 3 OCTA was performed twice and, the eyes were divided into 3 groups according to the TBUT (Group 1: TBUT ≤ 5 seconds, 43 eyes; Group 2: 5 seconds < TBUT ≤ 10 seconds, 35 eyes; Group 3: TBUT > 10 seconds, 34 eyes). The intraclass correlation coefficient, coefficient of variation, and test-retest SD were calculated and compared.

RESULTS

The signal strengths of OCTA were 9.1 ± 1.2, 9.5 ± 0.8, and 9.5 ± 0.8 in each group from Groups 1, 2, and 3, respectively, which showed significant difference (P = 0.049). The intraclass correlation coefficient of vessel density were 0.733, 0.840, and 0.974 in Groups 1 to 3, respectively, and the values increased in the order of Groups 1, 2, and 3. The coefficient of variation were 6.41 ± 6.09, 3.29 ± 2.22, and 1.30 ± 1.17, and the test-retest SD were 0.83 ± 0.70, 0.47 ± 0.31, and 0.19 ± 0.17 in Groups 1, 2, and 3, respectively. The coefficient of variation and test-retest SD values decreased in the order of Groups 1, 2, and 3, and showed a significant difference (all, P < 0.05).

CONCLUSION

The repeatability of OCTA tended to decrease with a shorter TBUT. When the TBUT is <5 seconds, care must be taken to interpret the OCTA results correctly.

Dynamics and mechanisms for tear breakup (TBU) on the ocular surface

The human tear film is rapidly established after each blink, and is essential for clear vision and eye health. This paper reviews mathematical models and theories for the human tear film on the ocular surface, with an emphasis on localized flows where the tear film may fail. The models attempt to identify the important physical processes, and their parameters, governing the tear film in health and disease.

Evaluation of objective visual quality in dry eye disease and corneal nerve changes

PURPOSE

To explore objective visual quality in dry eye diseases (DED) and the correlation between corneal nerves and objective visual quality.

METHODS

Ninety-eight eyes of 49 patients with DED were included. Each patient was evaluated with the ocular surface disease index (OSDI), eyelid margin signs and meibomian gland assessments; corneal staining; tear film breakup time (TBUT); tear meniscus height (TMH); in vivo confocal microscopic (IVCM); objective visual quality including the objective scatter index (OSI), mean objective scattering index (mOSI), modulation transfer function (MTF) cutoff value and Strehl ratio.

RESULTS

A significant correlation was found between the OSDI and mOSI (r = 0.422, p = 0.005), MTF cutoff value (r = - 0.355, p = 0.020), and Strehl ratio (r = - 0.446, p = 0.003). The OSI was significantly correlated with TBUTf (r = - 0.213, p = 0.042). The mOSI, MTF cutoff value, Strehl ratio were correlated with eyelid margin signs and meibomian assessments. Additionally, there was a statistically significant correlation between corneal nerve length and the mOSI (r = - 0.239, p = 0.037), OSI (r = - 0.294, p = 0.028), MTF cutoff value(r = 0.282, p = 0.012), and Strehl ratio (r = 0.299, p = 0.008).

CONCLUSIONS

Our study explored that objective visual quality was correlated with clinical symptoms and signs in DED patients. Furthermore, for the first time, our study explored the relationship between corneal nerves and objective visual quality and discovered that longer and wider corneal nerves were associated with better objective visual quality, which suggested that nerve changes may be a factor that related to poor visual quality in DED patients.

Boosted visual performance after eye blinks

We blink more often than required for maintaining the corneal tear film. Whether there are perceptual or cognitive consequences of blinks that may justify their high frequency is unclear. Previous findings showed that blinks may indicate switches between large-scale cortical networks, such as dorsal attention and default-mode networks. Thus, blinks may trigger a refresh of visual attention. Yet, this has so far not been confirmed behaviorally. Here, we tested the effect of blinks on visual performance in a series of rapid serial visual presentation tasks. In Experiment 1, participants had to identify a target digit embedded in a random stream of letter distractors, presented foveally for 60 ms each. Participants blinked once during the presentation stream. In a separate condition, blinks were simulated by shutter glasses. Detection performance was enhanced (up to 13% point increase in accuracy) for targets appearing up to 300 ms after eye blinks. Performance boosts were stronger for voluntary blinks than artificial blinks. This performance boost was also replicated with more naturalistic stimuli (Experiment 2). We conclude that eye blinks lead to attentional benefits for object recognition in the period after reopening of the eyelids and may be used strategically for temporarily boosting visual performance.

Structural and Molecular Tear Film Changes in Glaucoma

The Tear Film (TF) is a trilaminar and dynamic fluid covering the entire Ocular Surface (OS), consisting of a mucus, aqueous, and lipid layer deeply interacting between them. Because of its structure and functions, TF plays a pivotal role in the preservation of the OS integrity and the quality of vision. Medical therapy for glaucoma is recognized to profoundly disturb the OS homeostasis by altering all components of the ocular surface unit, including TF. The presence of preservatives, the number of daily eye drops instillations, and the duration of therapy are the main contributors to TF changes. From the physio-pathological side, TF alterations are induced by toxic and allergic mechanisms and result from goblet cell and Meibomian gland loss, dysfunction of accessory lacrimal glands, and epithelial disruption. In detail, TF changes are represented by mucus layer thinning, reduced mucin concentration, aqueous layer volume reduction, and lipid layer thinning with increased tear evaporation. Hyper- osmolarity and instability represent the main hallmarks of these changes and are an expression of a iatrogenic form of dry eye. TF undergoes also molecular modifications that primarily reflect a therapy- or disease-induced inflammatory status of the OS. Over the last years, this field of research aimed a progressively growing interest since molecular variations may be considered as potential candidate biomarkers of glaucoma. The aim of this review is to report the main TF changes occurring during glaucoma, exploring the relationship they may have with the glaucoma-related ocular surface disease and the patient quality of life, and their utility as potential biomarkers of disease.

Assessment of tear film optical quality in a young short tear break-up time dry eye: Case-control study

BACKGROUND

The aim of the study was to evaluate the dynamic changes of tear film optical quality in a short tear break-up time (TBUT) dry eye by using a double-pass system.

METHODS

Thirty-five short TBUT dry eye participants and 43 control subjects without dry eye were included in this study. One eye for each subject was analyzed. The Objective Scatter Index (OSI), modulation transfer function (MTF), and strehl ratio (SR) were recorded within a 20-second period with the participants asked to blink freely, and 10 successive seconds of nonblinking immediately after a blink was recorded to analyze the tear film OSI. The mean tear film OSI in 10 successive seconds, ΔOSI, and ΔOSI/time were evaluated. The correlation between tear film OSI and MTF, and the correlation between tear film OSI and MIT were also analysed.

RESULTS

Short TBUT dry eye participants showed significant deterioration of MTF and SR compared to control subjects. The mean tear film OSI in 10 successive seconds was significantly higher in dry eye participants than in control subjects. The mean OSI of the tear film (0-5 seconds) and the mean OSI of the tear film (6-10 seconds) were significantly higher in dry eye participants than in control participants. Moreover, the ΔOSI was significantly higher in dry eye participants than in control participants. The tear film OSI was significantly correlated with the MTF and the SR.

CONCLUSIONS

The tear film OSI of short TBUT dry eye participants is significantly increased in the early stage. Tear film instability in short TBUT dry eye participants has a significant effect on optical quality.

Impact of Dry Eye on Prolonged Reading

SIGNIFICANCE

Patients with dry eye frequently report difficulty with reading. However, the impact of dry eye on reading has not been studied in detail. This study shows the unfavorable effect of dry eye on reading speed and offers mechanisms that may be responsible.

PURPOSE

The purpose of this study was to evaluate the impact of dry eye signs as well as symptoms on both short-duration out-loud and prolonged silent reading.

METHODS

This study included 116 patients with clinically significant dry eye, 39 patients with dry eye symptoms only, and 31 controls, 50 years or older. After the Ocular Surface Disease Index (OSDI) questionnaire, objective testing of dry eye (tear film stability studies, Schirmer's test, and ocular surface staining) was performed. Total OSDI score and two subscores (vision related and discomfort related) were calculated. A short-duration out-loud reading test and a 30-minute sustained silent reading test were performed. Reading speed for each test was calculated as words per minute (wpm) and compared across the three groups.

RESULTS

Patients with clinically significant dry eye read slower than controls measured with sustained silent reading test (240 vs. 272 wpm, P = .04), but not with short-duration out-loud reading test (146 vs. 153 wpm, P = .47). Patients with dry eye symptoms only did not have slower reading speed measured using either reading test as compared with controls. However, vision-related OSDI subscore independently was associated with slower reading speed (P = .02). Multivariable regression models demonstrated that each 1-point (between 0 and 6) increase in corneal staining score led to a 10-wpm decrease in sustained silent reading speed (P = .01).

CONCLUSIONS

This study demonstrates a significant negative impact of dry eye (particularly presence of corneal staining) on prolonged reading. Prolonged reading task may serve as an objective clinically relevant test to measure the impact of dry eye on vision-related quality of life.

Effects of Blink Rate on Tear Film Optical Quality Dynamics with Different Soft Contact Lenses

Objective

The aim of this study was to investigate tear film optical quality dynamics for four types of silicone hydrogel contact lenses (SHCLs) for daily wear over a 15-day period and for different blink rate (BR) patterns.

Methods

A prospective randomized, double-blind, cross-over pilot study including four SHCLs (A: lotrafilcon B (Air Optix plus HydraGlyde, Alcon Laboratories); B: samfilcon A (Ultra, Bausch & Lomb); C: comfilcon A (Biofinity, CooperVision); and D: filcom V3 (Blu:gen, Mark'Ennovy)). Serial measurements of Objective Scatter Index (OSI) using the HD Analyzer (Visiometrics S.L., Terrassa, Spain) were taken at different blinking patterns: blinking every 2.5 seconds (high BRs) and every 9 seconds (low BRs). They were performed during the first visit before CL insertion (baseline), after 20 minutes of CL wear (Day 1), and during the last visit after 8 hours of CL wear on day 15 of use (Day 15).

Results

Normal young healthy subjects were recruited and fitted with the four lenses. For low BRs, the mean OSI value increased over time for all CLs and the slope of the curve also increased for all CLs, except for CL D. However, for high BRs, the mean OSI value increased only for CLs B and C and the slope of the curve did not change over time for any of them.

Conclusions

These results suggest that the tear film optical quality dynamics after wearing SCHLs for 15 days seems to undergo a slight deterioration only for lowest BR.

A comparative study of the quality of non-stimulated and stimulated tears in normal eye male subjects using the tear ferning test

PURPOSE

To evaluate and compare the tear ferning patterns of non-stimulated and stimulated tears in normal eye male subjects using the tear ferning test.

METHODS

Thirty-five male subjects aged 20-38 years with normal eyes were enrolled in the study. Subjects with dry eye or with a risk factor for eye dryness (eg, recent ocular surgery, contact-lens wearers, smokers, anemic, diabetes, and thyroid gland problems) were excluded from the study. Dry eye subjects were excluded based on the ocular surface diseases index scores, non-invasive tear break-up time, and tear meniscus height measurements from the right and left eyes. A tear sample was collected from both eyes in each subject to perform the tear ferning test for non-stimulated tears. After 10 mins, the tears were stimulated using a Schirmer strip, a tear sample was collected from both eyes in each participant, the tear ferning test was performed, and the ferns were graded based on the five-point tear ferning grading scale.

RESULTS

The average tear ferning grade [median (interquartile range)] for non-stimulated tears from the right and left eyes was 0.60 (1.25) and 0.50 (1.31), respectively. For stimulated tears, the average tear ferning grade from the right and left eyes was 0.50 (1.05) and 0.75 (1.25), respectively. There was no significant difference in the tear ferning grades obtained from non-stimulated and stimulated tears (Wilcoxon test, P>0.05).

CONCLUSION

This study found no significant difference in the tear ferning patterns obtained from non-stimulated and stimulated tears, or between the tear ferning patterns in the tears collected from the right and left eyes before and after stimulating tears. It seems that there were no changes in the chemical composition of tears before and after stimulation, possibly due to the steady concentration of electrolytes and lipids within the tear film for both non-stimulated and stimulated tears.

Corneal Sensory Experience via Transient Receptor Potential Vanilloid 1 Accelerates the Maturation of Neonatal Tearing

Tearing maturates rapidly after birth, and external environmental challenges play a key role in promoting lacrimal functional maturation. However, little is known about the facilitative factors underlying this developmental process or the potential of application of these factors to treat hypofunction of the lacrimal gland. In this study, eye opening and the subsequent ocular surface sensory experience, which is thought to be involved in postnatal maturation of lacrimal function, were investigated. Our results demonstrated that eye opening after birth is essential for the maturation of neonatal tearing. The maturation process of lacrimal function is dependent on the ocular surface sensory experience via transient receptor potential cation channel subfamily member 1 after birth. This study provides, for the first time, important evidence of the sensory experience of the ocular surface in relation to the maturation of functional tear secretion during the postnatal period.

Comparison of the impact of nesofilcon A hydrogel contact lens on the ocular surface and the comfort of presbyopic and non-presbyopic wearers

AIM

To assess and compare the impact of a daily disposable contact lens (CL) with high water content on the ocular surface and comfort of the presbyopic and non-presbyopic population after one day of use.

METHODS

Totally 20 presbyopes and 30 non-presbyopes non-contact wearers were fitted with nesofilcon A CLs. CL thickness was measured to assess material stability during daily wear, and ocular surface parameters were also assessed. Optical quality was analyzed for all cases. In addition, CL comfort was rated.

RESULTS

No significant differences were found in CL thickness, tear film osmolarity, average tear break-up time, bulbar redness, central corneal thickness, corneal volume, root-mean-square of higher-order aberrations (RMS of HOAs) and vertical and horizontal coma, either as a function of the group or time of use. A significant decrease in tear meniscus height and first break-up of the tear film was found in the presbyopic group (P=0.038; P=0.007 respectively). A decrease in spherical aberration coefficient was found after CL insertion (P=0.031 monofocal CL; P=0.023 low addition multifocal CL; P=0.016 high addition multifocal CL). Multifocal CL were thicker than monofocal CL (P=0.045). Comparison between groups showed more discomfort in presbyopes than non-presbyopes (P=0.003).

CONCLUSION

This study evidence that the behavior of the daily disposable CL with high water content seems to be stable during the day of use. Ocular parameters measured during wear show that CL behavior is the same for presbyopes and non-presbyopes, being more uncomfortable for presbyopes.

Unified approach to tear film surface analysis with high-speed videokeratoscopy

Placido disk videokeratoscopy, when used in a dynamic acquisition mode, can be utilized for noninvasive assessment of tear film quality. The different commercially available videokeratoscopes that incorporate an automatic option to evaluate tear film do not provide consistent measurements due to differences in their designs as well as differences in the algorithms used to analyze the images. Here, a standardized algorithm that can be applied to different instruments is developed. Results show that, by applying the proposed methodology in two different videokeratoscopes, the agreement among the estimated tear film parameters considerably improves. This represents a step forward in the normalization of tear film assessment.

[Tear film analysis and evaluation of optical quality: A review of the literature (French translation of the article)]

Dry eye is a complex multifactorial disease of the ocular surface and tears. It is associated with ocular surface symptoms and is one of the most common causes for ophthalmologic consultation. Despite their frequent use in clinical practice, the usual tests to evaluate dry eye and ocular surface disease-history of symptoms, tear break-up time (TBUT), Meibomian gland evaluation, corneal fluorescein staining, Schirmer test-have shown low reproducibility and reliability. In addition, subjective symptoms are often weakly or poorly correlated with objective signs. Since the tear film is the first system through which light must pass, the optical quality of the eye is highly dependent on the homogeneity of the tear film. Various investigative methods have been developed to evaluate both the structural and functional quality of the tear film, such as corneal topography, interferometry, tear meniscus measurement, evaporation rate, tear osmolarity and even aberrometry. Some are easily accessible to clinicians, while others remain in the field of clinical research. All of these tests provide a better understanding of the pathophysiology of the tear film. This review hopes to provide an overview of the existing tests and their role in evaluating the significance of the tear film in visual function.

Tear film analysis and evaluation of optical quality: A review of the literature

Dry eye is a complex multifactorial disease of the ocular surface and tears. It is associated with ocular surface symptoms and is one of the most common causes for ophthalmologic consultation. Despite their frequent use in clinical practice, the usual tests to evaluate dry eye and ocular surface disease-history of symptoms, tear break-up time (TBUT), Meibomian gland evaluation, corneal fluorescein staining, Schirmer test-have shown low reproducibility and reliability. In addition, subjective symptoms are often weakly or poorly correlated with objective signs. Since the tear film is the first system through which light must pass, the optical quality of the eye is highly dependent on the homogeneity of the tear film. Various investigative methods have been developed to evaluate both the structural and functional quality of the tear film, such as corneal topography, interferometry, tear meniscus measurement, evaporation rate, tear osmolarity and even aberrometry. Some are easily accessible to clinicians, while others remain in the field of clinical research. All of these tests provide a better understanding of the pathophysiology of the tear film. This review hopes to provide an overview of the existing tests and their role in evaluating the significance of the tear film in visual function.

Mechanobiology of the corneal epithelium

There has been a drive to develop new cell based therapies to treat corneal blindness, one of the most common causes of blindness worldwide. Mechanical and physical cues are known to regulate the behavior of many cell types, however studies examining these effects on corneal epithelial cells have been limited in number and their findings have not previously been amalgamated and contrasted. Here, we provide an overview of the different types of mechanical stimuli to which the corneal epithelium is exposed and the influence that these have on the cells. Shear stress from the tear film motion and blinking, extracellular matrix stiffness and external physical forces such as eye rubbing and contact lens wear are among some of the forms of mechanical stimuli that the epithelium experiences. In vivo and in vitro studies examining the mechanobiology on corneal epithelial cells under differing mechanical environments are explored. A greater understanding of the mechanobiology of the corneal epithelium has the potential to lead to improved tissue engineering and cell based therapies to repair and regenerate damaged cornea.

Immediate effect of a tear enhancer and meibomian gland expression on the corneal surface and whole eye higher order aberrations

PURPOSE

To investigate changes in higher order ocular aberrations (HOA) induced by the administration of 0.15% sodium hyaluronate tear enhancer (TE) and meibomian gland expression (ME) on the tear film of normal subjects.

METHODS

HOA values were obtained from the corneal surface (CS) and whole eye (WE), using a corneal topographer and Shack-Hartmann aberrometer, from both eyes of 50 subjects (25 females, mean age±sd 32.5±11.0 years, and 25 males, 33.88±11.2 years) for two pupil sizes (3 and 6mm) in a dark environment. One drop of Blink Contacts™ (Abbott Medical Optics) was instilled into the right eye and HOA measurements repeated after 30s. After 1h, the meibomian glands of the left lower eyelid were gently squeezed and HOA measurements repeated after 30s.

RESULTS

There was no significant difference for CS and WE root mean square (RMS) HOAs between right and left eyes before (both pupil sizes) and after TE use or ME (3mm pupil). For 6mm pupil, TE use significantly reduced the WE RMS HOA (p<0.05, mean±sd) for Z40 (0.297±0.136 to 0.053±0.069), and Z55 (0.221±0.372 to 0.098±0.121) while ME significantly increased CS RMS HOA (p<0.05, mean±sd) for Z3-3 (0.799±1.178 to 1.302±1.991) and Z44 (0.594±1.184 to 0.988±1.463). In general, the change in HOA was significantly correlated with the initial value before TE use or ME (p<0.05).

CONCLUSION

There were no detectable differences between right and left eyes. For the 6mm pupil, the tear enhancer tended to improve optical performance of the WE and meibomian gland expression tended to reduce the optical performance at the CS.

Useful In Vitro Techniques to Evaluate the Mucoadhesive Properties of Hyaluronic Acid-Based Ocular Delivery Systems

Polymer-based eye drops are the most used drug delivery system to treat dry eye disease (DED). Therefore, the mucoadhesion between the polymer and the ocular mucin is crucial to ensure the efficacy of the treatment. In this context, the present study aimed to evaluate the potential use of in vitro methods to study the mucoadhesion of eye drop solutions and, specifically to evaluate the efficacy of two hyaluronic acid-based formulations (HA), HA 0.15% and 0.30% (w/v) to treat DED. Rheology methods and zeta potential determination were used to study the mucoadhesive properties of both eye drop solutions. All results indicated that interactions occurred between the mucin and the HA, being stronger with HA 0.30%, due to the physical entanglements and hydrogen bounding. In vitro tests on ARPE-19 cell line were performed using a 2D and a 3D dry eye model and the results have shown that pre-treated cells with HA showed a morphology more similar to the hydrated cells in both products, with a high survival rate. The in vitro techniques used in this study have been shown to be suitable to evaluate and predict mucoadhesive properties and the efficacy of the eye drops on relief or treatment of DED. The results obtained from these methods may help in inferring possible in vivo effects.

On tear film breakup (TBU): dynamics and imaging

We report the results of some recent experiments to visualize tear film dynamics. We then study a mathematical model for tear film thinning and tear film breakup (TBU), a term from the ocular surface literature. The thinning is driven by an imposed tear film thinning rate which is input from in vivo measurements. Solutes representing osmolarity and fluorescein are included in the model. Osmolarity causes osmosis from the model ocular surface, and the fluorescein is used to compute the intensity corresponding closely to in vivo observations. The imposed thinning can be either one-dimensional or axisymmetric, leading to streaks or spots of TBU, respectively. For a spatially-uniform (flat) film, osmosis would cease thinning and balance mass lost due to evaporation; for these space-dependent evaporation profiles TBU does occur because osmolarity diffuses out of the TBU into the surrounding tear film, in agreement with previous results. The intensity pattern predicted based on the fluorescein concentration is compared with the computed thickness profiles; this comparison is important for interpreting in vivo observations. The non-dimensionalization introduced leads to insight about the relative importance of the competing processes; it leads to a classification of large vs small TBU regions in which different physical effects are dominant. Many regions of TBU may be considered small, revealing that the flow inside the film has an appreciable influence on fluorescence imaging of the tear film.

Corneal backward scattering and higher-order aberrations in children with vernal keratoconjunctivitis and normal topography

PURPOSE

To investigate the corneal backward scattering and higher-order aberrations (HOAs) in children with vernal keratoconjunctivitis (VKC) and normal topography.

METHODS

Thirty-six eyes of 22 patients with VKC and 54 eyes of 34 normal subjects were included. All participants had clear cornea, absence of dry eyes and a normal corneal tomography. Scheimpflug imaging was used to measure corneal backward scattering in zones centred on the corneal apex (central 2-mm zone and paracentral 2- to 6-mm zone), and HOAs were compared between VKC and normal control.

RESULTS

The mean age of participants was 12.0 ± 4.1 years in VKC group and 11.2 ± 4.1 years in control group (p = 0.339). There was no significant intergroup difference in mean keratometry, astigmatism and apex pachymetry (p ≥ 0.076). Total corneal backscatter was higher in the VKC group compared to the control group (p ≤ 0.012). Anterior and posterior cornea displayed a higher level of backward scattering in the VKC group (p < 0.001 for anterior; p ≤ 0.048 for posterior). Patients with VKC exhibited higher total HOAs and coma (p ≤ 0.036). There were significant correlations between total anterior HOAs and backward scattering measured at the central (r = 0.500; p = 0.032) and paracentral zones (r = 0.470; p = 0.024) for VKC.

CONCLUSION

The current study showed optical quality changes in patients with clear corneas and quiescent VKC. An increase in corneal backward scattering and HOAs was noted in patients with VKC as compared to normal patients.

Comparison of optical quality after implantable collamer lens implantation and wavefront-guided laser in situ keratomileusis

AIM

To compare the optical quality after implantation of implantable collamer lens (ICL) and wavefront-guided laser in situ keratomileusis (WG-LASIK).

METHODS

The study included 40 eyes of 22 patients with myopia who accepted ICL implantation and 40 eyes of 20 patients with myopia who received WG-LASIK. Before surgery and three months after surgery, the objective scattering index (OSI), the values of modulation transfer function (MTF) cutoff frequency, Strehl ratio, and the Optical Quality Analysis System (OQAS) values (OVs) were accessed. The higher order aberrations (HOAs) data including coma, trefoil, spherical, 2^nd astigmatism and tetrafoil were also obtained. For patients with pupil size <6 mm, HOAs data were analyzed for 4 mm-pupil diameter. For patients with pupil size ≥6 mm, HOAs data were calculated for 6 mm-pupil diameter. Visual acuity, refraction, pupil size and intraocular pressures were also recorded.

RESULTS

In both ICL and WG-LASIK group, significant improvements in visual acuities were found postoperatively, with a significant reduction in spherical equivalent (P< 0.001). After the ICL implantation, the OSI decreased slightly from 2.34±1.92 to 2.24±1.18 with no statistical significance (P=0.62). While in WG-LASIK group, the OSI significantly increased from 0.68±0.43 preoperatively to 0.91±0.53 postoperatively (Wilcoxon signed ranks test, P=0.000). None of the mean MTF cutoff frequency, Strehl ratio, OVs showed statistically significant changes in both ICL and WG-LASIK groups. In the ICL group, there were no statistical differences in the total HOAs for either 4 mm-pupil or 6 mm-pupil. In the WG-LASIK group, the HOA parameters increased significantly at 4 mm-pupil. The total ocular HOAs, coma, spherical and 2^nd astigmatism were 0.12±0.06, 0.06±0.03, 0.00±0.03, 0.02±0.01, respectively. After the operation, these values were increased into 0.16±0.07, 0.08±0.05, -0.04±0.04, 0.03±0.01 respectively (Wilcoxon signed ranks test, all P<0.05). At 6 mm-pupil, the induction of total HOAs was not statistically significant in the WG-LASIK group.

CONCLUSION

ICL implantation has a less disturbance to optical quality than WG-LASIK. The OQAS is a valuable complementary measurement to the wavefront aberrometers in evaluating the optical quality.

Computed flow and fluorescence over the ocular surface

Fluorescein is perhaps the most commonly used substance to visualize tear film thickness and dynamics; better understanding of this process aids understanding of dry eye syndrome which afflicts millions of people. We study a mathematical model for tear film flow, evaporation, solutal transport and fluorescence over the exposed ocular surface during the interblink. Transport of the fluorescein ion by fluid flow in the tear film affects the intensity of fluorescence via changes in concentration and tear film thickness. Evaporation causes increased osmolarity and potential irritation over the ocular surface; it also alters fluorescein concentration and thus fluorescence. Using thinning rates from in vivo measurements together with thin film equations for flow and transport of multiple solutes, we compute dynamic results for tear film quantities of interest. We compare our computed fluorescent intensity distributions with in vivo observations. A number of experimental features are recovered by the model.

Comparison of objective optical quality measured by double-pass aberrometry in patients with moderate dry eye: Normal saline vs. artificial tears: A pilot study

Dry eye is defined by a tear film instability resulting in variable but systematic fluctuations in quality of vision. Variability in optical quality can be demonstrated using a double pass aberrometer such as the Optical Quality Analyzing System, Visiometrics (OQAS). The goal of this work is to compare fluctuations in objective quality of vision measured by OQAS between treatment with normal saline eye drops and treatment with carmellose 0.5% and hyaluronic acid 0.1% (Optive Fusion [OF], Allergan) in patients with moderate dry eye syndrome. Optical quality was measured by evaluating the variations in the Optical Scattering Index (OSI) over 20seconds using the OQAS. Inclusion criteria were dry eye syndrome with an ocular surface disease index (OSDI) score >23 treated only with artificial tears. The patients were their own controls: OF in one eye and normal saline in the fellow eye. The choice of the subject eye and control eye was determined in a randomized fashion. OSI variations were measured in each eye before instillation, 5minutes and 2hours after instillation. The primary endpoint was OSI fluctuation over 20seconds of measurement. Secondary endpoints were the number of blinks and patient preference (preferred eye). Preliminary results were obtained on 19 patients. Average OSDI score was 36.8. Visual acuity was 10/10 with no significant difference between the two eyes. Prior to instillation, there was no significant difference between "normal saline" and "OF" eyes in terms of OSI, OSI variability or number of blinks. In the normal saline eye, there were no significant variations in mean OSI, OSI variability, OSI slope, or number of blinks. However, in the "OF" eye, there was a significant variation between initial and 2-hour OSI variability (0.363 versus 0.204, P<0.05), the average slope of OSI (0.04 versus 0.01, P<0.05) and the number of blinks (4.2 versus 2.8, P<0.05). Among the patients, 65% preferred the OF eye, 24% did not have a preference, and 11% preferred the normal saline eye. Objective quality of vision measured by OQAS is an interesting parameter for evaluating the effectiveness of a lacrimal substitute. The purpose of artificial tears is, among other things, to provide comfort and a reduction of dry eye symptoms such as poor quality of vision. This study demonstrates that 0.5% carmellose and 0.1% hyaluronic acid allowed better stabilization of the tear film and thus a significant improvement in the quality of vision compared to normal saline.

Blink: Characteristics, Controls, and Relation to Dry Eyes

Blink is a complex phenomenon that is profoundly affected by diverse endogenous and exogenous stimuli. It has been studied in the context of cognition, emotional, and psychological states, as an indicator of fatigue and sleepiness, particularly in the automobile and transportation industry, in visual tasking, and finally, as it relates to tear film stability and ocular surface health. The fact that it is highly variable and has input from so many sources makes it very difficult to study. In the present review, the behavior of blink in many of these systems is discussed, ultimately returning in each instance to a discussion of how these factors affect blink in the context of dry eyes. Blink is important to ocular surface health and to an individual's optimal functioning and quality of life. Disturbances in blink, as cause or effect, result in a breakdown of tear film stability, optical clarity, and visual function.

Use of the Controlled Adverse Environment (CAE) in Clinical Research: A Review

The many internal and external factors that contribute to the pathophysiology of dry eye disease (DED) create a difficult milieu for its study and complicate its clinical diagnosis and treatment. The controlled adverse environment (CAE^®) model has been developed to minimize the variability that arises from exogenous factors and to exacerbate the signs and symptoms of DED by stressing the ocular surface in a safe, standardized, controlled, and reproducible manner. By integrating sensitive, specific, and clinically relevant endpoints, the CAE has proven to be a unique and adaptable model for both identifying study-specific patient populations with modifiable signs and symptoms, and for tailoring the evaluation of interventions in clinical research studies.

Mechanisms, imaging and structure of tear film breakup

Tear film breakup (BU) is an important aspect of dry eye disease, as a cause of ocular aberrations, irritation and ocular surface inflammation and disorder. Additionally, measurement of breakup time (BUT) is a common clinical test for dry eye. The current definition of BUT is subjective; here, a more objective concept of "touchdown" - the moment when the lipid layer touches down on the corneal surface - is proposed as an aid to understanding processes in early and late stages of BU development. Models of BU have generally been based on the assumption that a single mechanism is involved. In this review, it is emphasized that BU does not have a single explanation but it is the end result of multiple processes. A three-way classification of BU is proposed - "immediate," "lid-associated," and "evaporative." Five different types of imaging systems are described, which have been used to help elucidate the processes involved in BU and BUT; a new method, "high resolution chromaticity images," is presented. Three directions of tear flow - evaporation, osmotic flow out of the ocular surface, and "tangential flow" along the ocular surface - determine tear film thinning between blinks, leading to BU. Ten factors involved in BU and BUT, both before and after touchdown, are discussed. Future directions of research on BU are proposed.

Effect of diquafosol three per cent ophthalmic solution on tear film and corneal aberrations after cataract surgery

BACKGROUND

The aim was to evaluate the effect of diquafosol on tear film parameters and corneal aberrations after cataract surgery.

METHODS

This retrospective, comparative, observational case series included patients who underwent cataract surgery with or without peri-operative use of diquafosol three per cent ophthalmic solution. Patients in group I (31 eyes) were treated with diquafosol three per cent ophthalmic solution six times a day from one week before surgery to three months after surgery. Patients in group II (33 eyes) underwent cataract surgery without being administered diquafosol. Tear film break-up time (BUT), the ocular surface disease index (OSDI), the Oxford Scheme score, Schirmer's test I and corneal aberrations were determined before and at one and three months post-surgery.

RESULTS

In group I, the BUT, OSDI and Oxford Scheme score showed significant improvement at one and three months post-surgery (p = 0.002 for BUT at one month and three months, p = 0.023 and p = 0.049 for OSDI at one month and three months and p = 0.001 and p = 0.026 for Oxford Scheme at one month and three months), compared to baseline. In group II, the BUT, OSDI and Oxford Scheme score did not show any significant improvement during the follow-up period. In both groups, Schirmer's test I significantly decreased at three months post-surgery (p = 0.011 for group I and p = 0.034 for group II), compared to baseline. There were significant differences in the BUT and OSDI between the groups at three months post-surgery (p = 0.037 for BUT and p = 0.011 for OSDI). Regarding the corneal aberration, there were no significant differences between the groups at three months post-surgery.

CONCLUSION

Peri-operative application of diquafosol three per cent ophthalmic solution may prevent dry eye-related ocular surface changes accompanied by improvement of ocular symptom. No definite changes in corneal aberrations were noted.

Changes of Corneal Wavefront Aberrations in Dry Eye Patients after Treatment with Artificial Lubricant Drops

Purpose. To evaluate the corneal aberration changes in dry eye patients after treatment with artificial eye drops. Methods. Thirty mild to moderate dry eye patients treated with artificial eye drops and twenty comparable dry eye patients were recruited as controls. Anterior corneal aberrations over 3 mm and 5 mm analytical zones including total, 3rd to 5th high order aberrations (HOAs), spherical aberration (SA), and vertical (V-coma) and horizontal coma (H-coma) obtained from corneal topography data at baseline and 2 weeks after treatment were evaluated. Results. For 3 mm zone, trefoils, V-coma, H-coma terms, and 3rd and 5th HOAs were significantly decreased (p < 0.05) in the treatment group. For 5 mm zone, instillation of eye drops reduced H-coma, SA terms, 3rd to 5th orders, and total HOAs all showed a significant decrease (p < 0.05). The root mean square analysis of the Zernike terms also showed similar statistical results. For control group, all individual terms and total HOAs did not have significant changes over 3 mm and 5 mm zones (p > 0.05). Conclusions. Treatment with artificial eye drops can effectively improve the corneal optical quality of dry eye patients by ameliorating the HOAs of anterior corneal surface.

Corneal topography in keratoconus: state of the art

The morphological characterization of the cornea using corneal topographers is a widespread clinical practice that is essential for the diagnosis of keratoconus. The current state of this non-invasive exploratory technique has evolved with the possibility of achieving a great number of measuring points of both anterior and posterior corneal surfaces, which is possible due to the development of new and advanced measurement devices. All these data are later used to extract a series of topographic valuation indices that permit to offer the most exact and reliable clinical diagnosis. This paper describes the technologies in which current corneal topographers are based on, being possible to define the main morphological characteristics that the keratoconus pathology produces on corneal surface. Finally, the main valuation indices, which are provided by the corneal topographers and used for the diagnosis of keratoconus, are also defined.

Effectiveness and Optical Quality of Topical 3.0% Diquafosol versus 0.05% Cyclosporine A in Dry Eye Patients following Cataract Surgery

Purpose. To evaluate the effectiveness and optical quality of 3.0% topical diquafosol versus 0.05% cyclosporine A in dry eye patients following cataract surgery. Methods. In total, 40 eyes of 40 patients newly diagnosed with dry eye syndrome 1 week after cataract surgery were randomized to receive either 3.0% diquafosol ophthalmic solution six times daily or 0.05% cyclosporine A twice daily for 3 months. Outcome measures were tear film break-up time (TBUT), results on Schirmer 1 test, ocular surface staining score, the ocular surface disease index (OSDI) score, and higher-order aberrations (HOAs). Measurements were taken at baseline and at 1, 2, and 3 months. Results. In the diquafosol group, TBUT showed higher outcomes than the cyclosporine A group at 1 and 3 months. Both groups showed increased scores on Schirmer 1 test. The ocular surface staining score decreased in all periods in both groups. Vertical coma and total HOAs decreased more in the cyclosporine A group than in the diquafosol group at 3 months. Conclusion. Both 3.0% diquafosol and 0.05% cyclosporine A were effective in treating dry eye after cataract surgery. Diquafosol was more effective in increasing the tear secretion, but cyclosporine A was more effective in improving optical aberrations.

Evaluation of the impact of persistent subepithelial corneal infiltrations on the visual performance and corneal optical quality after epidemic keratoconjunctivitis

PURPOSE

Aim was to measure the effect of persistent subepithelial corneal infiltrates (SEIs) after epidemic keratoconjunctivitis (EKC) on visual performance and corneal optical quality.

METHODS

We examined 53 patients divided into two groups. Patients with previous EKC constituted the study group (Group 1, n: 27). Healthy age matched subjects constituted the control group (Group 2, n: 26). Study group was subdivided into eyes with SEI (Group 1A, 40 eyes) and healthy fellow eyes (Group 1B, 14 eyes). Patients were submitted to a complete examination including high- and low-contrast visual acuities (HCVA, LCVA), corneal topography and aberrometry.

RESULTS

The mean interval between epidemic conjunctivitis and examination was 7.25 ± 5.63 months. Mean number of corneal infiltrates was 17.30 ± 14.38. The mean HCVA and LCVA were significantly lower in the eyes with SEI than fellow eyes and control group (p = 0.001). LCVA value was also worse in the fellow eyes when compared to control (p = 0.048). Corneal topography values were significantly higher in the eyes with SEI from both fellow eyes and control group. During corneal aberrometry, the mean root mean square value of spheric aberration, irregular astigmatism and total aberration were significantly higher in SEI group when compared to fellow eyes and control group (p < 0.05). Total aberrations were higher than control subjects in the fellow eyes. Trefoil aberration was higher in SEI group only when compared to control subjects, while there was no significant difference in coma aberration values between the groups (p > 0.05).

CONCLUSION

Results of this study suggested that visual performance is compromised in patients with EKC by aberrations and changes in topographic variables.

Tear metabolite changes in keratoconus

While efforts have been made over the years, the exact cause of keratoconus (KC) remains unknown. The aim of this study was to identify alterations in endogenous metabolites in the tears of KC patients compared with age-matched healthy subjects. Three groups were tested: 1) Age-matched controls with no eye disease (N = 15), 2) KC - patients wearing Rigid Gas permeable lenses (N = 16), and 3) KC - No Correction (N = 14). All samples were processed for metabolomics analysis using LC-MS/MS. We identified a total of 296 different metabolites of which >40 were significantly regulated between groups. Glycolysis and gluconeogenesis had significant changes, such as 3-phosphoglycerate and 1,3 diphosphateglycerate. As a result the citric acid cycle (TCA) was also affected with notable changes in Isocitrate, aconitate, malate, and acetylphosphate, up regulated in Group 2 and/or 3. Urea cycle was also affected, especially in Group 3 where ornithine and aspartate were up-regulated by at least 3 fold. The oxidation state was also severely affected. Groups 2 and 3 were under severe oxidative stress causing multiple metabolites to be regulated when compared to Group 1. Group 2 and 3, both showed significant down regulation in GSH-to-GSSG ratio when compared to Group 1. Another indicator of oxidative stress, the ratio of lactate - pyruvate was also affected with Groups 2 and 3 showing at least a 2-fold up regulation. Overall, our data indicate that levels of metabolites related to urea cycle, TCA cycle and oxidative stress are highly altered in KC patients.

Evaluation of corneal optical properties in subjects wearing hydrogel etafilcon A contact lenses and the effect of administering mannitol-enriched sodium hyaluronate ophthalmic solution

BACKGROUND

The purpose of this study was to evaluate the effect of daily administration of mannitol-enriched sodium hyaluronate ophthalmic solution on the corneal optical properties of subjects wearing low Dk hydrogel (etafilcon A) contact lenses (CLs).

METHODS

Forty-five subjects wearing etafilcon A CLs daily for more than 6 months were recruited into this pilot study. Fifteen of the subjects administered a 10% mannitol-enriched 0.05% sodium hyaluronate solution (study group) once daily and 30 subjects did not administer any ophthalmic solution (control group). The subjects were examined at baseline and one month after recruitment. Changes in central corneal thickness (CCT) and corneal light backscatter were evaluated by Scheimpflug imaging (Pentacam HR). Changes in corneal total high-order aberration, corneal spherical aberration, coma, and trefoil were evaluated using the OPD scan II.

RESULTS

At one month, corneal light backscatter decreased significantly in the study group (≤18.30 arbitrary units; P<0.05) and this was highly correlated with a decrease in CCT (R=0.81; P=0.04). The decrease in corneal total high-order aberration, spherical aberration, and coma was significantly higher in the study group than in the control group (P<0.05). No changes in corneal light backscatter or CCT were found in the control group during follow-up.

CONCLUSION

Once-daily administration of a mannitol-enriched lubricant ophthalmic solution was effective for improving the corneal optical quality and reducing corneal swelling in subjects wearing low Dk hydrogel (etafilcon A) CLs during one month follow-up.