Acta Ophthalmologica 2015
Effect of hyaluronic acid on tear film thickness as assessed with ultra-high resolution optical coherence tomography Semira Kaya,1,2,3 Doreen Schmidl,1,2 Leopold Schmetterer,1,2 Katarzyna J. Witkowska,1,2 Angelika Unterhuber,1 Valentin Aranha dos Santos,1 Carina Baar,2 Gerhard Garho¨fer2 and Rene´ M. Werkmeister1 1
Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria 3 Department of Ophthalmology, Paracelsus University Salzburg, Salzburg, Austria 2
ABSTRACT. Purpose: The aim of this study was to assess the effect of a single drop of hyaluronic acid on tear film thickness (TFT) in healthy subjects. Methods: Sixteen healthy subjects (eight male/eight female) aged between 20 and 36 years were included in this randomized, double-masked placebocontrolled study. One eye received a single dose of hyaluronic acid (Olixia pure; Croma Pharma, Korneuburg, Austria) eye drops, and the fellow eye received physiologic saline solution as placebo control. The study eye was chosen randomly. TFT as measured with a custom-built Fourier-domain optical coherence tomography (FD-OCT) system was the main outcome variable and measured before and every 10 min until 1 hr after topical administration. Results: Baseline TFT was 4.8 0.5 lm in the study eye and 5.0 0.4 lm in the control eyes. Hyaluronic acid significantly increased TFT (p = 0.008 versus placebo) with a maximum effect 10 min after instillation (13.9 11.9%). Post hoc analysis revealed that an increase in TFT was seen until 30 min after administration compared to placebo. Data in the placebo group show high reproducibility with an intraclass correlation coefficient of 0.93 and a coefficient of variation of 5.4 3.3%. Conclusion: The data of this study indicate that hyaluronic acid increases TFT for as long as 30 min in healthy subjects. In addition, our data provide evidence that our custom-built OCT system is capable of measuring residence time of lubricants on the ocular surface. Key words: dry eye – hyaluronic acid – optical coherence tomography – randomized placebocontrolled study – tear film thickness
Acta Ophthalmol. 2015: 93: 439–443 ª 2015 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd
doi: 10.1111/aos.12647
Introduction Dry eye syndrome (DES) is a common disease of the ocular surface that involves tear film instability, inflammation and hyperosmolarity (Lemp et al.
2007; Calonge et al. 2010; Sweeney et al. 2013). The therapy of DES particularly in the early stages is mainly based on lubricants. A wide variety of polymers has been used as the basis for lubricants: hydroxypropyl methylcellu-
lose, carboxy methylcellulose, polyvinyl alcohol, carbopol, polyvinylpyrrolidone, polyethylene glycol, dextran, hyaluronic acid (HA) or carbomer 940 (Murube et al. 1998; Doughty & Glavin 2009). HA has gained much interest and wide spread application in lubricants, because it is naturally occurring and shows excellent biocompatibility and unique viscoelastic properties (Rah 2011). A wide variety of studies has also shown that HA protects corneal epithelial cells against different types of damage and stimulates epithelial migration (Nishida et al. 1991; Gomes et al. 2004; Pauloin et al. 2009; Wu et al. 2011, 2013). Evaluating the treatment success of therapies in DES is a major challenge. This is related to the weak correlation between signs and symptoms in DES (Sullivan et al. 2014), but also to the high variability of signs such as break-up time (BUT) or Schirmer test (Lemp et al. 2007). Recently, with the improved resolution and sensitivity of optical coherence tomography (OCT), several groups have attempted to measure tear film thickness (TFT) using this technology (Wang et al. 2006; Chen et al. 2010; Yadav et al. 2011; Kottaiyan et al. 2012; Qiu et al. 2012). We have introduced a Fourier-domain optical coherence tomography (FDOCT) system using a broadband Ti: sapphire laser as light source providing a resolution of 1.2 lm in tissue
439
Acta Ophthalmologica 2015
(Schmoll et al. 2012; Werkmeister et al. 2013). In this study, we hypothesized that administration of HA may lead to an increase in TFT as measured with OCT. This was performed in an effort to characterize the residence time of HA on the ocular surface.
Material and Methods Subjects
The study was performed in accordance with the Declaration of Helsinki and the Good Clinical Practice (GCP) guidelines of the European Union. Before start of the study, the protocol was approved by the Ethics Committee of the Medical University of Vienna. 16 healthy male and female subjects were included in this study after written informed consent was given. The sample size calculation was based on a paired t-test with a power of 80% and a two-sided alpha level of 0.05. The clinically relevant difference between treatments is considered 10%. The standard deviation of the main outcome variable (TFT) has been published previously (Werkmeister et al. 2013). During the 4 weeks before the first study day, all subjects had to complete a prestudy screening, which included medical history, vital signs, and determination of height and weight. In women, a urine pregnancy test was performed. Every subject also passed an ophthalmic examination including visual acuity using the ETDRS acuity chart, Schirmer I test, slit lamp biomicroscopy and indirect funduscopy, measurement of BUT and measurement of intra-ocular pressure (IOP) with Goldmann applanation tonometry. Inclusion criteria were an age of at least 18 years, normal findings in the medical history unless the investigator considered an abnormality to be clinically irrelevant, normal ophthalmic findings and an ametropia 10 mm and BUT >10 seconds were included. The participants were not allowed to use any concomitant medication during the 3 weeks before the first study day. Subjects with a difference of more than 5 mm in Schirmer I test or difference of >3 seconds in BUT between the two eyes were excluded from participation.
440
Study design
This study was performed in a randomized, double-masked, placebo-controlled study design. The eye drops were randomly assigned to the right or left eye on the study day (randomization 1:1), whereas the fellow eye received placebo. HA eye drops (0.15%) used in the present study also contained purified water, sodium chloride, disodium phosphate and leontopodium alpinum (Edelweiss) extract (Olixia pure eye drops; Croma Pharma GmbH, Austria). Physiological sodium chloride solution (0.9%) was used as placebo. In the study eye, one drop equalling approximately 35 ll of the medical product has been administered, while in the control eye (fellow eye), one drop of placebo has been instilled. The instillation was always performed in the right eye first immediately followed by the left eye. On the trial day, a 20-min resting period in a sitting position was scheduled to get adapted to the experimental setting. Thereafter, baseline measurements of TFT were performed using OCT. Then, the medical device and placebo were instilled in the two eyes, respectively. OCT measurements were performed every 10 min after instillation for 1 hr. All examinations were carried out in a dimly lit consulting room under the same conditions with a room temperature in the range of 20–23°C and humidity in the range of 40–60%. Methods Measurement of TFT using OCT
The custom-built OCT system that was used for TFT measurements has been described in detail previously (Werkmeister et al. 2013). The light source (Ti:sapphire laser; Integral OCT; Femto-lasers Produktions GmbH, Vienna, Austria) has a central wavelength of 800 nm and a full width at half maximum (FWHM) bandwidth of 170 nm, resulting in a theoretical axial resolution of 1.2 lm in corneal tissue. The transverse resolution of the employed OCT system is 21 lm at the front surface of the cornea. The power of the incident light focused onto the cornea was set to 600 lW, which is less than a tenth of the maximum permissible exposure as specified by ANSI (American National Standards Institute) and IEC 60825-1 (International Electrotechnical Commission). The
optics and the spectrometer are optimized for the broad bandwidth to ensure utilization of the full spectrum. For the present experiments, the highspeed CCD camera (e2v EM4CL 2014; Aviva, Essex, UK) was operated at an acquisition rate of 45 kHz. The lightdelivery system of the sample arm is mounted on a modified slit lamp headrest to minimize head movements and to allow precise alignment of the probe beam onto the subject’s eye. Subjects were asked to look straightforward onto an internal fixation target and to blink normally during the alignment procedure that took about 10 seconds. Thereafter, subjects were advised to blink once and measurement started immediately after opening of the eyes. Three volumes with a size of 4 mm 9 4 mm 9 1 mm (horizontal 9 vertical 9 depth) were acquired within 3 seconds, each containing 512 9 128 9 1024 voxels. For calculation of central TFT, in each volume, the 15 horizontal frames above the central specular reflex of the probe beam at the apex of the cornea were postprocessed (Werkmeister et al. 2013). The mean of determined thickness values for the three recorded volumes gave the actual TFT for the specific measurement session. Break-up time
Tear break-up time was measured following the guidelines published in the Report of the International Dry Eye WorkShop (2007). Briefly, 35 ll of Minims fluorescein sodium 2.0% eye drops were applied in the conjunctival sac of the eye. The subject was instructed to blink naturally without squeezing several times to distribute the fluorescein. Within 10–30 seconds after fluorescein instillation, the subject was asked to stare straight ahead without blinking, until told otherwise. By means of a stopwatch, the time between last complete blink and first appearance of a dry spot was recorded. Once break-up of the tear film was observed, the subject was instructed to blink freely. Schirmer I test
Schirmer I test (without anaesthesia) was performed following the guidelines published in the Report of the International Dry Eye WorkShop (2007). Briefly, the test was performed as follows: Schirmer paper strips were inserted in the unanesthetized eye over
Acta Ophthalmologica 2015
the lower lid margin, mid-way between the middle and outer third. The subject was then asked to close the eye. After a time of 5 min, the wetting of the Schirmer paper was measured. Data analysis
An ANOVA model for repeated measurements was employed to assess significant differences between HA and placebo. To assess differences in timepoints, planned comparisons were used as post hoc tests within the ANOVA model. To quantify reliability of measurements, intraclass correlation coefficients (k) were calculated (Bartko & Carpenter 1976) using the data of the placebo day. The calculation of k is based on a repeated measure ANOVA model using the variance among subjects (vs), the variance among measurements (vM) and the residual error variance (ve) and is calculated as k¼
vs ve : vs þ ve þ 2vM
ð1Þ
A k of 1 means perfect reproducibility. The higher the intraclass correlation coefficient, the lesser is the variability of the method. In addition, the coefficients of variation (CV) were calculated from the data of the placebo eye. The standard deviation (SD) was calculated for each subject individually and divided by the individual mean of TFT to calculate the coefficient of variation. As a measure of reproducibility, the mean and SD of these individual CVs are presented. A two-tailed p-value of 0.05 was considered the level of significance. All statistical analysis was carried out using CSS Statistica (Version 6.0; Tulsa, OK, USA).
Baseline TFT values were comparable between the study and the control eyes (study eye: 4.8 0.5 lm, control eye: 5.0 0.4 lm, p = 0.47 between eyes). Topical administration of HA increased TFT as measured with OCT (p = 0.008 ANOVA versus placebo, Fig. 1). The maximum increase in TFT was seen 10 min after administration (13.9 11.9%, p = 0.013 post hoc analysis versus placebo). The increase in TFT was also significant at 20 min after administration (13.7 10.8%, p = 0.009 post hoc analysis versus placebo) and at 30 min after administration (13.0 11.9%, p = 0.034 post hoc analysis versus placebo). In some subjects, the effect was even seen for a longer period of time. Exemplary OCT images of a baseline measurement and a measurement 30 min after topical instillation of HA are shown in Fig. 2. As can be seen easily, the administration of HA led to an increase in central TFT as compared to the baseline value. Using the seven consecutive measurements from the eyes receiving placebo, an intraclass correlation coefficient of 0.93 was calculated. The high degree of reproducibility was also evident from the coefficient of variation, which amounted to 5.4 3.3%.
Discussion The present study indicates that HA increases TFT by approximately 14% in healthy subjects, an effect that lasts for approximately 30 min. The present study also indicates that these effects
can be quantified using the custombuilt OCT system described previously (Werkmeister et al. 2013). This is related to the high resolution and reproducibility of the measurement system and thus indicates excellent sensitivity to detect changes after a standardized measurement protocol. The present study shows that an increase in precorneal TFT caused by the administration of HA can be detected in healthy subjects for as long as 30 min and indicates a residence time of approximately half an hour on the ocular surface. Little is known about the residence time of different lubricants at the ocular surface. Generally, it is considered that more viscous substances stay longer on the ocular surface, a reason for the fact that some clinicians prefer them in the treatment of DES to obtain longer patient comfort (Geerling et al. 2011). Our results are in good agreement with clinical data indicating that both 0.1% HA and 0.3% HA lead to longer-lasting relief of symptoms than saline (Johnson et al. 2006). The authors attributed this effect to a longer-lasting residence time of HA on the ocular surface, which is supported by the results of the present study. Indeed, Polack and McNiece have shown that 0.2% HA has significantly longer ocular surface residence times than 0.3% hydroxymethylcellulose or 1.4% polyvinyl alcohol (Polack & McNiece 1982). Results as obtained using quantitative gamma scintigraphy are in good accordance with our data, although it needs to be considered that in this study, dry eye patients were
Results Sixteen healthy volunteers aged between 20 and 36 years (eight male and eight female subjects, mean age 27 5 years) participated in this study. The baseline for BUT was 13.3 2.5 seconds and 13.6 2.7 seconds in the study and control eye, respectively (p = 0.76 between eyes). There was also no difference between Schirmer I (study eye: 18.8 8.3 mm, control eye: 18.7 8.7 mm, p = 0.85 between eyes) and IOP (study eye: 15.4 2.2 mm, control eye: 15.4 2.3 mm, p = 0.80 between eyes) between the study and control eye.
Fig. 1. Effects of hyaluronic acid (HA) or placebo on tear film thickness as assessed with OCT. Data are presented as % change over baseline (means SD; n = 16).
441
Acta Ophthalmologica 2015
(A)
(B) Fig. 2. Exemplary OCT images (A) before and (B) 30 min after instillation of HA. An increase in tear film thickness in the order of 1.5 lm can be seen in (B).
included (Snibson et al. 1990). The authors compared the effects of either 0.2% HA or 0.3% HA with polymerfree buffered saline. In patients with DES, a mean ocular surface residence time for 0.3% HA of 23.5 min was reported. For 0.2% HA, the mean ocular surface residence time was 11.1 min, whereas placebo stayed for
Effect of hyaluronic acid on tear film thickness as assessed with ultra-high resolution optical coherence tomography Semira Kaya,1,2,3 Doreen Schmidl,1,2 Leopold Schmetterer,1,2 Katarzyna J. Witkowska,1,2 Angelika Unterhuber,1 Valentin Aranha dos Santos,1 Carina Baar,2 Gerhard Garho¨fer2 and Rene´ M. Werkmeister1 1
Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria 3 Department of Ophthalmology, Paracelsus University Salzburg, Salzburg, Austria 2
ABSTRACT. Purpose: The aim of this study was to assess the effect of a single drop of hyaluronic acid on tear film thickness (TFT) in healthy subjects. Methods: Sixteen healthy subjects (eight male/eight female) aged between 20 and 36 years were included in this randomized, double-masked placebocontrolled study. One eye received a single dose of hyaluronic acid (Olixia pure; Croma Pharma, Korneuburg, Austria) eye drops, and the fellow eye received physiologic saline solution as placebo control. The study eye was chosen randomly. TFT as measured with a custom-built Fourier-domain optical coherence tomography (FD-OCT) system was the main outcome variable and measured before and every 10 min until 1 hr after topical administration. Results: Baseline TFT was 4.8 0.5 lm in the study eye and 5.0 0.4 lm in the control eyes. Hyaluronic acid significantly increased TFT (p = 0.008 versus placebo) with a maximum effect 10 min after instillation (13.9 11.9%). Post hoc analysis revealed that an increase in TFT was seen until 30 min after administration compared to placebo. Data in the placebo group show high reproducibility with an intraclass correlation coefficient of 0.93 and a coefficient of variation of 5.4 3.3%. Conclusion: The data of this study indicate that hyaluronic acid increases TFT for as long as 30 min in healthy subjects. In addition, our data provide evidence that our custom-built OCT system is capable of measuring residence time of lubricants on the ocular surface. Key words: dry eye – hyaluronic acid – optical coherence tomography – randomized placebocontrolled study – tear film thickness
Acta Ophthalmol. 2015: 93: 439–443 ª 2015 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd
doi: 10.1111/aos.12647
Introduction Dry eye syndrome (DES) is a common disease of the ocular surface that involves tear film instability, inflammation and hyperosmolarity (Lemp et al.
2007; Calonge et al. 2010; Sweeney et al. 2013). The therapy of DES particularly in the early stages is mainly based on lubricants. A wide variety of polymers has been used as the basis for lubricants: hydroxypropyl methylcellu-
lose, carboxy methylcellulose, polyvinyl alcohol, carbopol, polyvinylpyrrolidone, polyethylene glycol, dextran, hyaluronic acid (HA) or carbomer 940 (Murube et al. 1998; Doughty & Glavin 2009). HA has gained much interest and wide spread application in lubricants, because it is naturally occurring and shows excellent biocompatibility and unique viscoelastic properties (Rah 2011). A wide variety of studies has also shown that HA protects corneal epithelial cells against different types of damage and stimulates epithelial migration (Nishida et al. 1991; Gomes et al. 2004; Pauloin et al. 2009; Wu et al. 2011, 2013). Evaluating the treatment success of therapies in DES is a major challenge. This is related to the weak correlation between signs and symptoms in DES (Sullivan et al. 2014), but also to the high variability of signs such as break-up time (BUT) or Schirmer test (Lemp et al. 2007). Recently, with the improved resolution and sensitivity of optical coherence tomography (OCT), several groups have attempted to measure tear film thickness (TFT) using this technology (Wang et al. 2006; Chen et al. 2010; Yadav et al. 2011; Kottaiyan et al. 2012; Qiu et al. 2012). We have introduced a Fourier-domain optical coherence tomography (FDOCT) system using a broadband Ti: sapphire laser as light source providing a resolution of 1.2 lm in tissue
439
Acta Ophthalmologica 2015
(Schmoll et al. 2012; Werkmeister et al. 2013). In this study, we hypothesized that administration of HA may lead to an increase in TFT as measured with OCT. This was performed in an effort to characterize the residence time of HA on the ocular surface.
Material and Methods Subjects
The study was performed in accordance with the Declaration of Helsinki and the Good Clinical Practice (GCP) guidelines of the European Union. Before start of the study, the protocol was approved by the Ethics Committee of the Medical University of Vienna. 16 healthy male and female subjects were included in this study after written informed consent was given. The sample size calculation was based on a paired t-test with a power of 80% and a two-sided alpha level of 0.05. The clinically relevant difference between treatments is considered 10%. The standard deviation of the main outcome variable (TFT) has been published previously (Werkmeister et al. 2013). During the 4 weeks before the first study day, all subjects had to complete a prestudy screening, which included medical history, vital signs, and determination of height and weight. In women, a urine pregnancy test was performed. Every subject also passed an ophthalmic examination including visual acuity using the ETDRS acuity chart, Schirmer I test, slit lamp biomicroscopy and indirect funduscopy, measurement of BUT and measurement of intra-ocular pressure (IOP) with Goldmann applanation tonometry. Inclusion criteria were an age of at least 18 years, normal findings in the medical history unless the investigator considered an abnormality to be clinically irrelevant, normal ophthalmic findings and an ametropia 10 mm and BUT >10 seconds were included. The participants were not allowed to use any concomitant medication during the 3 weeks before the first study day. Subjects with a difference of more than 5 mm in Schirmer I test or difference of >3 seconds in BUT between the two eyes were excluded from participation.
440
Study design
This study was performed in a randomized, double-masked, placebo-controlled study design. The eye drops were randomly assigned to the right or left eye on the study day (randomization 1:1), whereas the fellow eye received placebo. HA eye drops (0.15%) used in the present study also contained purified water, sodium chloride, disodium phosphate and leontopodium alpinum (Edelweiss) extract (Olixia pure eye drops; Croma Pharma GmbH, Austria). Physiological sodium chloride solution (0.9%) was used as placebo. In the study eye, one drop equalling approximately 35 ll of the medical product has been administered, while in the control eye (fellow eye), one drop of placebo has been instilled. The instillation was always performed in the right eye first immediately followed by the left eye. On the trial day, a 20-min resting period in a sitting position was scheduled to get adapted to the experimental setting. Thereafter, baseline measurements of TFT were performed using OCT. Then, the medical device and placebo were instilled in the two eyes, respectively. OCT measurements were performed every 10 min after instillation for 1 hr. All examinations were carried out in a dimly lit consulting room under the same conditions with a room temperature in the range of 20–23°C and humidity in the range of 40–60%. Methods Measurement of TFT using OCT
The custom-built OCT system that was used for TFT measurements has been described in detail previously (Werkmeister et al. 2013). The light source (Ti:sapphire laser; Integral OCT; Femto-lasers Produktions GmbH, Vienna, Austria) has a central wavelength of 800 nm and a full width at half maximum (FWHM) bandwidth of 170 nm, resulting in a theoretical axial resolution of 1.2 lm in corneal tissue. The transverse resolution of the employed OCT system is 21 lm at the front surface of the cornea. The power of the incident light focused onto the cornea was set to 600 lW, which is less than a tenth of the maximum permissible exposure as specified by ANSI (American National Standards Institute) and IEC 60825-1 (International Electrotechnical Commission). The
optics and the spectrometer are optimized for the broad bandwidth to ensure utilization of the full spectrum. For the present experiments, the highspeed CCD camera (e2v EM4CL 2014; Aviva, Essex, UK) was operated at an acquisition rate of 45 kHz. The lightdelivery system of the sample arm is mounted on a modified slit lamp headrest to minimize head movements and to allow precise alignment of the probe beam onto the subject’s eye. Subjects were asked to look straightforward onto an internal fixation target and to blink normally during the alignment procedure that took about 10 seconds. Thereafter, subjects were advised to blink once and measurement started immediately after opening of the eyes. Three volumes with a size of 4 mm 9 4 mm 9 1 mm (horizontal 9 vertical 9 depth) were acquired within 3 seconds, each containing 512 9 128 9 1024 voxels. For calculation of central TFT, in each volume, the 15 horizontal frames above the central specular reflex of the probe beam at the apex of the cornea were postprocessed (Werkmeister et al. 2013). The mean of determined thickness values for the three recorded volumes gave the actual TFT for the specific measurement session. Break-up time
Tear break-up time was measured following the guidelines published in the Report of the International Dry Eye WorkShop (2007). Briefly, 35 ll of Minims fluorescein sodium 2.0% eye drops were applied in the conjunctival sac of the eye. The subject was instructed to blink naturally without squeezing several times to distribute the fluorescein. Within 10–30 seconds after fluorescein instillation, the subject was asked to stare straight ahead without blinking, until told otherwise. By means of a stopwatch, the time between last complete blink and first appearance of a dry spot was recorded. Once break-up of the tear film was observed, the subject was instructed to blink freely. Schirmer I test
Schirmer I test (without anaesthesia) was performed following the guidelines published in the Report of the International Dry Eye WorkShop (2007). Briefly, the test was performed as follows: Schirmer paper strips were inserted in the unanesthetized eye over
Acta Ophthalmologica 2015
the lower lid margin, mid-way between the middle and outer third. The subject was then asked to close the eye. After a time of 5 min, the wetting of the Schirmer paper was measured. Data analysis
An ANOVA model for repeated measurements was employed to assess significant differences between HA and placebo. To assess differences in timepoints, planned comparisons were used as post hoc tests within the ANOVA model. To quantify reliability of measurements, intraclass correlation coefficients (k) were calculated (Bartko & Carpenter 1976) using the data of the placebo day. The calculation of k is based on a repeated measure ANOVA model using the variance among subjects (vs), the variance among measurements (vM) and the residual error variance (ve) and is calculated as k¼
vs ve : vs þ ve þ 2vM
ð1Þ
A k of 1 means perfect reproducibility. The higher the intraclass correlation coefficient, the lesser is the variability of the method. In addition, the coefficients of variation (CV) were calculated from the data of the placebo eye. The standard deviation (SD) was calculated for each subject individually and divided by the individual mean of TFT to calculate the coefficient of variation. As a measure of reproducibility, the mean and SD of these individual CVs are presented. A two-tailed p-value of 0.05 was considered the level of significance. All statistical analysis was carried out using CSS Statistica (Version 6.0; Tulsa, OK, USA).
Baseline TFT values were comparable between the study and the control eyes (study eye: 4.8 0.5 lm, control eye: 5.0 0.4 lm, p = 0.47 between eyes). Topical administration of HA increased TFT as measured with OCT (p = 0.008 ANOVA versus placebo, Fig. 1). The maximum increase in TFT was seen 10 min after administration (13.9 11.9%, p = 0.013 post hoc analysis versus placebo). The increase in TFT was also significant at 20 min after administration (13.7 10.8%, p = 0.009 post hoc analysis versus placebo) and at 30 min after administration (13.0 11.9%, p = 0.034 post hoc analysis versus placebo). In some subjects, the effect was even seen for a longer period of time. Exemplary OCT images of a baseline measurement and a measurement 30 min after topical instillation of HA are shown in Fig. 2. As can be seen easily, the administration of HA led to an increase in central TFT as compared to the baseline value. Using the seven consecutive measurements from the eyes receiving placebo, an intraclass correlation coefficient of 0.93 was calculated. The high degree of reproducibility was also evident from the coefficient of variation, which amounted to 5.4 3.3%.
Discussion The present study indicates that HA increases TFT by approximately 14% in healthy subjects, an effect that lasts for approximately 30 min. The present study also indicates that these effects
can be quantified using the custombuilt OCT system described previously (Werkmeister et al. 2013). This is related to the high resolution and reproducibility of the measurement system and thus indicates excellent sensitivity to detect changes after a standardized measurement protocol. The present study shows that an increase in precorneal TFT caused by the administration of HA can be detected in healthy subjects for as long as 30 min and indicates a residence time of approximately half an hour on the ocular surface. Little is known about the residence time of different lubricants at the ocular surface. Generally, it is considered that more viscous substances stay longer on the ocular surface, a reason for the fact that some clinicians prefer them in the treatment of DES to obtain longer patient comfort (Geerling et al. 2011). Our results are in good agreement with clinical data indicating that both 0.1% HA and 0.3% HA lead to longer-lasting relief of symptoms than saline (Johnson et al. 2006). The authors attributed this effect to a longer-lasting residence time of HA on the ocular surface, which is supported by the results of the present study. Indeed, Polack and McNiece have shown that 0.2% HA has significantly longer ocular surface residence times than 0.3% hydroxymethylcellulose or 1.4% polyvinyl alcohol (Polack & McNiece 1982). Results as obtained using quantitative gamma scintigraphy are in good accordance with our data, although it needs to be considered that in this study, dry eye patients were
Results Sixteen healthy volunteers aged between 20 and 36 years (eight male and eight female subjects, mean age 27 5 years) participated in this study. The baseline for BUT was 13.3 2.5 seconds and 13.6 2.7 seconds in the study and control eye, respectively (p = 0.76 between eyes). There was also no difference between Schirmer I (study eye: 18.8 8.3 mm, control eye: 18.7 8.7 mm, p = 0.85 between eyes) and IOP (study eye: 15.4 2.2 mm, control eye: 15.4 2.3 mm, p = 0.80 between eyes) between the study and control eye.
Fig. 1. Effects of hyaluronic acid (HA) or placebo on tear film thickness as assessed with OCT. Data are presented as % change over baseline (means SD; n = 16).
441
Acta Ophthalmologica 2015
(A)
(B) Fig. 2. Exemplary OCT images (A) before and (B) 30 min after instillation of HA. An increase in tear film thickness in the order of 1.5 lm can be seen in (B).
included (Snibson et al. 1990). The authors compared the effects of either 0.2% HA or 0.3% HA with polymerfree buffered saline. In patients with DES, a mean ocular surface residence time for 0.3% HA of 23.5 min was reported. For 0.2% HA, the mean ocular surface residence time was 11.1 min, whereas placebo stayed for
