Development of Instant Measuring Model for Oxygen Permeability

and Water Content of Hydrogel Contact Lens

Chih-Wei Hung

, Kuo-Cheng Huang

, Hsin-Yi Tsai

, Yu-Hsuan Lin

and Patrick Joi-Tsang Shum

Instrument Technology Research Center, National Applied Research Laboratories, 20,

R&D Rd. VI. Hsinchu Science Park, 30076, Hsinchu City, Taiwan

Department of Ophthalmology, Cathay General Hospital, No. 2, Ln. 59,

Jiancheng Rd., Xizhi Dist, 22174, New Taipei City, Taiwan

Keywords: Hydrogel Contact Lens, Oxygen Permeability, Water Content, Dehydration Rate.

Abstract: The diffusion coefficient D, gas solubility k of material and the thickness of lens t were used to evaluate the

oxygen permeability Dk/t of contact lenses (CLs). However, the nominal value Dk/t is usually not consistent

with the actual oxygen permeability of wearing CL. As the oxygen travel through the hydrogel, it need to be

carried by water molecules in the lens material; thus, the higher the water content (WC) of the material, the

higher the Dk/t value. In order to obtain the WC and Dk/t of wearing CL, we create a testing platform to

simulate the wearing status of CL. When the light traveled through the lens, we found that the attenuation in

green light is smoother than other wavelengths. Moreover, the WC is higher, its dewatering rate at room

temperature is lower, and the light attenuation is relatively smaller. Comparing with the other CL of similar

WC, the Dk/t of CL is higher if it has higher dehydration. In the study, we evaluated the WC and Dk/t of

hydrogel CL based on the light attenuation in eight minutes. The attenuation degree of light after traveling

through the CL can be used to estimate the Dk/t of hydrogel CL.

1 INTRODUCTION

The contact lens (CL) can be divided into soft CL and

hard CL based on their material hardness, wherein the

main material of soft CLs are hydrated polymer and

hydroxyethyl methacrylate (HEMA), and the

traditional hard CL material are polymethyl metha-

crylate (PMMA). However, the PMMA was replaced

by the hydrophobic gas permeable material in recent

year. Because the soft CL is relatively soft, it is easily

attached to cornea; therefore, the patient will feel

more comfortable while wearing. However, the eyes

is prone to irritation or dryness if extended-wear CL,

because the eye covered by the CL is not easy to

contact with air. In addition, the high water content of

CL is readily to cause the microbial and bacterial

attachment, and a substantial increase of infection

rate in eyes, or even result in the proliferation of

capillaries around the eyes. On the contrary, the hard

CL will cause a foreign body sensation (FBS) in his

eyes when the patient begins to wear it, but has a

better correction effect for patients with high myopia

or astigmatism due to the smaller coverage area of

eye. Moreover, the hard CL which has a lower water

content is less susceptible to microbial and bacterial

attachment, so the infection rates of eyes dropped

significantly.

In accordance with (ISO-11539, 1999) standards

for the classification of soft CL, The CL material can

be classified by a six-part code. The category

classification is based on material composition,

oxygen permeability, etc., wherein the composition

can be distinguished depending on the compound of

silicon (Si) and fluorine (F) and the water content and

ionic monomers are also included. Hard CL can be

made from hexafocon, enflufocon or polymethyl

methacrylate (PMMA). Soft CL materials are mostly

2-hydroxy-ethyl methacrylate (HEMA), methacrylic

acid (MAA), methyl methacrylate (MMA), vinyl

pyrrolidone (VP), etc. (Tranoudis and Efron, 2004),

or can be stamper manufactured in different

proportions of these materials.

An important indicator to evaluate the quality of

CL is so-called oxygen permeability. In general, the

oxygen permeability of CL is denoted by Dk, where

D is the diffusion coefficient which represents the

ability of the gas diffusion through the CL material;

that is, the moving speed of the gas molecules in CL.

k is the solubility coefficient which indicates the

degree of dissolved oxygen in CL, and Dk is the

Hung C., Huang K., Tsai H., Lin Y. and Shum P.

Development of Instant Measuring Model for Oxygen Permeability and Water Content of Hydrogel Contact Lens.

DOI: 10.5220/0006107301750182

In Proceedings of the 5th International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS 2017), pages 175-182

ISBN: 978-989-758-223-3

175

product of the diffusion coefficient and solubility

coefficient. The units of Dk value are 10-11 (cm3 O2

cm)/ (cm3 sec mmHg) or "barrier". The higher is the

value of Dk, the better is the oxygen permeability of

CL. In addition, the Oxygen transmissibility (Dk/t) of

the local region of CL is expressed as oxygen

permeability (Dk) of the material of CL is divided by

the thickness (t) of CL.

There are two commonly methods to measure the

Dk or Dk/t of CL, the polarographic and coulometric

technologies (Fatt and Chaston, 1982, Refojo, et al.,

1977, Refojo and Leong, 1979, Brennan, et al., 1986,

Compañ, et al., 1996, Paterson and Doran, 1986 and

González-Méijome, et al., 2008). The polarographic

technique has often been used to determinate the Dk

coefficient of hydrogel CL, which placed directly on

the Clark-type electrode, based on the oxygen flux

through the CL. Practically, this technique has its

limitations during measuring Dk, such as the so-

called boundary-layer effect and edge effect in the

polarographic method. The boundary-layer effect

leads to the underestimation the Dk/t of sample due

to the difference of oxygen partial pressure on the two

side of sample. In addition, the edge effect means that

the lateral diffusion of oxygen occurs if the test area

is not the same on both sides of sample and results in

the Dk value of sample under test is slightly higher

than the real value. Despite these shortcomings in the

measurement of polarographic method, but it can use

some experimental procedure to amend its measured

value to close the actual value. For example, the

measuring values could be corrected by measuring

the samples of different thickness for the boundary-

layer effect (Compañ, 2002), or be multiplied by a

proper correction factor for the edge effect. In the

coulometric method, a nitrogen carrier gas flows

around the lens and transports the permeated oxygen

to the oxygen detector which produces an electrical

current, wherein the magnitude of oxygen through the

film is proportional to the amount of oxygen. The

oxygen gas transmits from upper chamber through

CL film into lower chamber during the permeability

process. However, the sample has a dehydration

effect during test when it exposed to air; therefore, the

coulometric method is not applied to the Dk

measurement of hydrogel CL because the water

content can cause changes in oxygen permeability.

The above mentioned two methods are both well

defined in the ISO standards (ISO 9913-1, 1996 and

ISO 9913-2, 2000), which also referred to the

restrictions on the use of two methods. The

polarographic method can only measure the CLs of

less than 100 Barrier, and the coulometric method

cannot be applied to the hydrogel CLs. However, the

polarographic (Fatt) and coulometric method in ISO

can be adopted to determinate the oxygen permeation

through all types of contact lenses, except the high Dk

silicone based CLs. Therefore, these standards 9913-

1&2 have now been withdrawn and replaced by (ISO

18369-3, 2006). The ISO 18369-3 specifies the

methods of testing the physicochemical properties of

CLs, which are extraction, rigid lens flexure and

breakage, oxygen permeability, refractive index and

water content. Therein, the soft CLs can also be made

of non-hydrogel materials, such as the silicone

elastomers. Based on the high performance liquid

chromatography (HPLC-EC), (Oberndorf and

Wilhelm, 2003) uses the reductive electrochemical

detection to determine oxygen at nanomolar levels,

the method had not only lens dehydration, but can

minimize the edge and boundary layer effects, the Dk

values of rigid and soft CL can be determined in the

same manner with good reproducibility. The above

mentioned measuring methods for oxygen

permeability of CLs are based on the electrochemical

or vacuum infiltration model, so the measuring results

are often not consistent due to the different measuring

method or instruments.

Therefore, this study presents a non-contact

method that can reduce the measurement error came

from the environment or instrument layout, and to

evaluate the WC and Dk/t of CL in different manner

from the absorption spectrum of CL. Therein, the full

wavelength of light was provided from the halogen

lamp, and the variation of light spectrum was

measured from the spectrometer that facing to the

light source. In addition, five types of CL with

different WC and Dk/t were employed to observe the

variation of intensity of transmission light in 8 minute

after wearing to the experimental setup.

2 FUNDEMENTAL THEORY AND

EXPERIMENT SYSTEM

2.1 Relationship between Water

Content and Oxygen Permeability

of Contact Lens

In general, the Dk/t of CLs is positive correlation to

the WC of CLs, (Hadassah and Sehgal, 2006)

presented a measurement that allowing the oxygen to

pass through the lens material and investigate the

oxygen permeability and transmissibility of contact

lenses of different thickness and curvature. Therein,

the expelled oxygen gas was collected by the

dissolution in ethanol and measured by the titration of

PHOTOPTICS 2017 - 5th International Conference on Photonics, Optics and Laser Technology

176

solvent, and this method could be employed in both

dry and wet conditions of lenses. The results showed

that the Dk value was directly proportional to the WC

of lens and inversely proportional to the thickness of

lens, shown as Fig. 1. Therefore, the WC of CLs while

wearing could be used to evaluate the oxygen

permeability of CLs.

Figure 1: Dk values of lens related to the water content.

(Hadassah and Sehgal, 2006).

2.2 The Spectrum of Oxygen and

Water Absorption

The substances have different light absorption,

reflectively and transmission while irradiated by the

light. (Hale and Querry, 1973) developed that the

relatively lower and stable absorption of light at

wavelength of 400-600 nm, shown as Fig. 2. In

addition, the oxygen also has lower absorbance and

evolution rate at wavelength of 500 – 650 nm,

shown as Fig. 3. Therefore, the intensity at

wavelength of 500 – 600 nm was analyzed to

investigate the variation of WC and Dk value while

wearing different CLs.

Figure 2: Absorption spectra of water. (Prahl, 2009).

Figure 3: Absorption and action spectrum of oxygen. (Taiz

and Zieger, 2015).

2.3 Development of Mathematical

Model

The attenuation (κ) of light intensity was determined

by intensity variation between without CLs (I

Ini

) and

wearing CLs (I

), and which was expressed as (1).

Ini

CLIni

II −

=(%)κ

(1)

The κ increase with the increase of WC due to the

CLs with high WC need more water to maintain its

properties. Therefore, the WC of wearing CLs could

be calculated when

ave

of each CLs in a period was

obtained, and the relationship could be expressed as

(2).

111

κκ(%) WC

aveave

×+×+=

γβα

(2)

where α

, β

, and γ

was the coefficient. In addition,

the variation (V

) between the maximum and

minimum κ in a period also could be evaluated by

WC, and written as (3),

222κ

WC δWCWC(%) V ×+×+×+=

γβα

(3)

where α

, β

, γ

and δ

was the coefficient. Moreover,

the oxygen permeability (Dk/t) of wearing CLs could

be evaluated simultaneously from the variation

attenuation of each CLs by Eqn. (4),

κ3κ33

/D VVtk ×+×+=

γβα

(4)

where α

, β

, and γ

was the coefficient.

2.4 Layout of Measuring System

In order to measure the actually Dk value while

wearing CL, the optical measuring module was build

in this study, and several different CLs were put on

the measuring module to investigate the variation of

light intensity in a period of time. Thus, the measuring

results and the properties such as WC and Dk/t while

wearing CLs were discussed.

Development of Instant Measuring Model for Oxygen Permeability and Water Content of Hydrogel Contact Lens

177

2.4.1 Setup of Experiment

In the experiment, the light source was the halogen

lamp with power of 150 watts, and the wavelength of

light ranged UV to NIR spectrum, especially 380 to

900 nm. A holder was fabricated by 3D printer to

place the CLs, and the SD1220-025-UVN spectro-

meter was placed at back of CLs and faced to the light

source to detect the transmission intensity of the light

beam. Therein, a 0.5D attenuator lens was used and

placed between the CLs and light source to decay the

light intensity that detected by spectrometer, shown

as Fig. 4.

Figure 4: Layout of the instant measuring setup for wearing

contact lens.

2.4.2 Process of Experiment

The experimental process was divided into four main

parts, shown as Fig. 5.

(1) Turned on the light source and fixed the light

intensity output from the light source by

controlling the current. In addition, connect the

spectrometer to the computer, and initialized the

spectrometer.

(2) Measure the transmission intensity directly from

the light source and 0.5D attenuator lens, and

determine the value as the reference; especially

without CLs on the holder.

(3) Put the tested CLs on the holder, and start to

count the time that exposed on the air.

(4) Measure the transmission intensity that through

the CLs, and save the date every 1 minute to

observe the variation of light intensity.

Measure transmission

intensity without CLs

Wearing CLs on

measuring setup

Measure transmission

intensity with CLs

(interval of 1 min)

Turn on light

source/spectrometer

Figure 5: Experimental process for measuring the Dk/t of

wearing CLs.

2.4.3 Preparation of Samples

In this study, five different types of CL from four

brands including NOIST, HYDRON, TICON and

BAUSCH+LOMB, and each of them has different

WC and Dk/t values, which were summarized in

Table 1. Therein, the samples of No. 1, 2, and 5 were

used to investigate the relationship of WC and decay

rate of spectrum, and the samples of No. 1, 3, and 4

with similar WC value were used to investigate the

relationship of the Dk/t and difference between

maximum and minimum of spectrum value in the

period of 8 minutes.

Table 1: Summarized of tested samples.

No. Brand/Model WC (%) Dk/t

MOIST/ACUVUE

1-day

58 33.3

HYDRON/Eye Secret

1-Day

38 26*

HYDRON/ UV Blocking

1-Day

55 30*

TICON/Hyaluronic Acid

1-Day

58 29

BAUSCH+LOMB/Bio true

1-Day

78 42

*: The maximum value in the interval.

3 EXPERIMENT RESULTS AND

DISCUSSIONS

The purpose of our research was to develop an

alternative to the conventional electrochemical or

vacuum infiltration method for measuring Dk/t values

of CL. To achieve our objective, we proposed an

optical technology, which offers the benefit of non-

contact skills and avoids measurement error with

different instrument that can lead the way to higher

reproducibility of measuring results. Four steps had

been taken in the experiment, so that we can evaluate

the WC and Dk/t by using the absorption spectrum of

CL.

3.1 Spectrum Intensity after Wearing

Contact Lenses

The first step of our research, three CLs with different

WC were measured using the non-contact optical

method as described in the formerly mentioned

section. The No. 1 CL had a WC of 38%, the No. 2

CL had a WC of 58% and the No.3 CL had a WC of

78%. Take the 38% WC of CL for example, the light

intensity of un-wearing CL and wearing CL can be

PHOTOPTICS 2017 - 5th International Conference on Photonics, Optics and Laser Technology

178

shown in Fig. 6. The difference between the two

curves can also illustrated in Fig. 6. Because the

original data can’t offer enough information, the

attenuation of light was used to analyse in this study.

3.2 Light Attenuation after Wearing

Contact Lenses

The light attenuation of CL No. 2 can be shown in

Fig. 7. During the experiment, we found that the

curve of light absorption rate in UV light provide a

highly unstable status. This phenomenon may be

caused by the measuring precision of spectrometer in

300-400 wavelength range and the basic ability of

anti-ultraviolet of CL. The IR wave range in 890 to

900 nm had been chosen as standard originally,

because the study by Prahl (Prahl, n.d.) indicates that

there is a high absorption rate of water in IR light. The

relationship between light attenuation and water

content can be built up by this wave band of light.

Figure 6: The light intensity with and without wearing

contact lens.

Figure 7: The light attenuation after wearing contact lens

one minute and eight minutes. (the upper right corner is the

enlarged view of 500-600 nm).

Unfortunately, Fig. 6 shows that there is a trend to

descent in IR wavelength, so that we can’t use the

results as basic. On the other hand, in fig. 7, we also

found that the attenuation of light in green

wavelength (500-600 nm) was smoother than others.

This results are entirely consistent with Hale’s results

(Hale and Querry, 1973). So that we chose the light

ranged from 500-600 nm as the reference, the partial

enlarged view is illustrated in Fig. 7.

3.3 Calculation of Water Content

When the contact lens is wearing on the human eyes,

it needs to keep humid from tears by blinking eyes;

otherwise, the contact lens will dry off in a period of

time. In second step of our research, we found that

contact lens was tendency to dry out after 8 minutes

in our simulation model; then it provided error

information caused by the surface cracks. Therefore,

we averaged spectral attenuation from 1 to 8 minutes,

the formula of attenuation was determined in Eqn.

(1). Our results in Fig. 8 indicate that with increasing

water content of contact lens, there is an increase in

light attenuation. The average attenuation of CL with

78% WC was about 17.1% in 8 minutes; the average

attenuation of CL with 58% WC was about 8.3%, and

the average attenuation of CL with 38% WC was

about 5.2%. From this results, we concluded that the

higher water content, the more water in contact lens.

Water is like a blocked layer which can resists the

light to get through the CL. Therefore, we can use

light attenuation to estimate the WC of an unknown

contact lens by Eqn. (2) which is derived from Fig.1.

The correlation coefficient α

, and γ

can be

calculated using Eqn. (2). Where

= -12.5025, β

11.64322 and γ

= -0.37138.

Figure 8: The fitting curve of the average attenuation and

water content.

Development of Instant Measuring Model for Oxygen Permeability and Water Content of Hydrogel Contact Lens

179

3.4 Calculation of Variation of Light

Attenuation

According to the knowledge in previous section, the

higher the WC of CL, the higher the Dk/t. However,

this linear relationship needs to be under ideal

conditions. When contact lens is worn on human eyes,

it will dry out along with the wearing time. Although

we blink several times to keep our eyes moist, it will

still discomfort when the CL becomes dry and the

WC isn’t maintaining the maximum value. From the

above reasons, we concluded that simple WC values

would not allow us to obtain the Dk/t values. In third

step of our research, we thus shift our attention to the

difference between maximum and minimum

attenuation of light in 8 minutes, the variation of light

attenuation can also be demonstrated in Fig. 8. In Fig.

9, the images show that the brand with 38% WC has

the highest difference value between max and min

attenuation rate. For each of the CLs, we found that

the WC increased with decreasing difference

attenuation. The difference was about 7 at 38% WC

of CL; the difference was about 4.5 at 58% of WC;

The difference was 3.8 at 78% of WC. The results

concept is intuitively and clear that the more water in

the CLs, the slower the moisture out of the CLs. The

equation of the difference of max and min attenuation

is express as Eqn. (3). Therefore, we can apply the

average of the attenuation in Eqn. (2), use the obtain

attenuation to calculate the water content. Then,

substituting WC in Eqn. (3) with Eqn. (2) yields the

relationship between WC and the difference of

maximum and minimum light attenuation. The value

of the difference attenuation was defined as a

correction factor in this research, which we can use

this factor to calculate Dk/t value in next section. The

correlation coefficient α

, β

, γ

and δ

can be

calculated using Eqn. (3). Where α

= 23.1557, β

= -

0.70445 and γ

= 0.00887 and δ

=-3.75×10

-5

Figure 9: The fitting curve between the variation of light

attenuation and water content.

3.5 Calculation of Oxygen Permeability

of Contact Lens

On the basic of the abstract discussed, when the

oxygen attempts to go through the material of

hydrogel, it needs to follow with water molecules in

the contact lenses; therefore, the higher the WC, the

higher the Dk/t. However, this research took two

kinds of popular CLs with both 58% WC to make a

comparison. It was found that, although the two kinds

of CLs shared the same WC, the Dk/t value of them

were totally different. So that, this research took a

correction factor that was derived by Eqn. (3) in

section 3.3 to solve the problem. During the

experiment, three brands of CLs with similar WC

were used to comparison in the fourth step of this

study. Sample No. 1, 3 and 4 in Table. 1 were used to

make comparison. Since the water content of the three

samples are not identical, the sample No. 3 with 55%

WC needs to be fixed. When Dk/t of CL is under 40,

there is a linear relationship between water content

and oxygen permeability that has been well described

by Hadassah (Hadassah and Sehgal, 2006). Due to the

relationship, Dk/t of sample No.3 can be corrected to

31.6, the revised values is illustrated in Table 2. Then,

the correction factor of section 3.3 were used as the

standard to establish the curve with Dk/t value.

Fig. 10 shows that the larger variation of light

attenuation, the larger the Dk/t value. The value of

light attenuation represents its hydrophobic ability.

When the hydrophobic ability is better, the oxygen

permeability is also higher. Use the results from

section 3.4, we can easily compute the Dk/t value by

the Eqn. (4).

In summary, from the above experiment results,

the model to collocate WC and Dk/t value has been

constructed. Eqn. (2) - (4) were used to calculated

WC and Dk/t by using light attenuation. The

correlation coefficient α

, β

, and γ

can be calculated

using Eqn. (4). Where α

= 3.9875, β

= 7.97879 and

= -0.53788. Since the new contact lens is soaking in

the water and is not at wearing status, the results

Table 2: Similar to the water content of tested samples.

No. Brand/Model WC (%) Dk/t

MOIST/ACUVUE

1-day

58 33.3

HYDRON/ UV Blocking

1-Day

55 30

HYDRON/ UV Blocking

1-Day (adjusted)

58* 31.6*

TICON/Hyaluronic Acid

1-Day

58 29

*: The value has been corrected.

PHOTOPTICS 2017 - 5th International Conference on Photonics, Optics and Laser Technology

180

obtained from the equation are slightly different from

the data on contact lens box. The accuracy of WC and

Dk/t values that calculated by this research are up to

95% to the value that contact lenses are practically

worn on human eyes, as long as the contact lens WC

is ranged from 38% to 78% and make from hydrogel.

Figure 10: The fitting curve of light attenuation and oxygen

transmissibility.

4 CONCLUSIONS

The CLs has gradually become more popular among

patients due to the benefits of beauty and comfort.

However, the human cornea does not have blood

vessels and it obtains oxygen directly through the air,

so it causes corneal angiogenesis when the cornea

was in a hypoxic state for a long period of time, and

even would lead to aging and permanent damage of

the cornea if seriously hypoxia. Therefore, the CLs

manufacturers continue to develop the gas permeable

hydrogel CLs for patents without corneal irritation

effects after a periods of wearing. Nowadays, the

presented measuring methods for the Dk/t and WC of

CLs are almost based on the electrochemical reaction

or permeabilization within two chamber methods, and

the measuring results cannot state any instant datum

for user; therefore, this study presents an optical

method that can evaluate instantly the WC and Dk/t

of CL depended on the absorption spectrum of CL.

In the instant method, when the light travelled

through the lens, we measure the light attenuation of

500- 600nm wavelength within eight minutes to

comparison of five kinds of well-known product in

market. The hydrogel CL is placed in a specific

holder, and the both sides will be dehydrated at the

same time, so that the light attenuation through CL in

eight minutes is gradually stability. In the experiment,

we found that the WC is an important factor of light

attenuation; the average light attenuation is higher,

the WC of CL is higher and the variation of light

attenuation is also the larger in eight minutes. In

addition, the variation of light attenuation is larger,

the oxygen permeability is also greater while

compared with the CL of similar WC. Furthermore,

computed from the light attenuation and its variation

through CL, we can build a real-time measurement

model for CL’s performance. In future, we can add

thickness t as a correction factor to calculate the real

Dk/t of contact lens with different dioptres and the

instant WC and Dk/t of CL can be estimated from the

light reflection when the eyes wearing the CL.

ACKNOWLEDGEMENTS

This work has been supported in part by the Ministry

of Science and Technology, Taiwan, under Grants

MOST 105-2221-E-492-016-

REFERENCES

ISO 11539: 1999. Ophthalmic Optics- Contact Lenses-

Classification of Contact Lenses and Contact Lens

Material.

Tranoudis, I., Efron, N., 2004. “Water properties of soft

contact lens materials”, Contact Lens Anterior Eye, 27,

193-208.

Fatt, I., Chaston, J., 1982. “Measurement of Oxygen

Transmissibility and Permeability of Hydrogel Lenses

and Materials”, Int. Contact Lens Clin, 9, 76-88.

Refojo, M. F., Holly, F. J., Leong, F. L., 1977.

“Permeability of Dissolved Oxygen through Contact

Lenses I. Cellulose Acetate Butyrate”, Contact

Intraocular Lens Medical J., 3, 27-33.

Refojo, M. F., Leong, F. L., 1979. “Water-Dissolved-

Oxygen Permeability Coefficients of Hydrogel

Contact-Lenses and Boundary-Layer Effects”, J.

Membr. Sci., 4, 415-426.

Brennan, N., Efron, N., Holden, B. A., 1986. “Oxygen

Permeability of Hard Gas Permeable Contact Lens

Materials”, Clin. Exp. Optom., 69, 82-89.

Compañ, V., Villar, M. A., Vallés, E. M., Riande, E., 1996.

“Permeability and Diffusional Studies on Silicone

Polymer Networks with Controlled Dangling Chains”.

Polymer, 37, 101-107.

Paterson, R., Doran, P. A., 1986. “Spray Technique for the

Determination of Membrane Diffusion and Distribution

Coefficients by the Time-Lag Method: Evaluated for

Electrolyte Transport through Charged and Uncharged

Membranes”, J. Membr. Sci., 26, 289-301.

González-Méijome, J. M., Compañ-Moreno,V., Riande, E.,

2008. “Determination of oxygen permeability in soft

contact lenses using a polarographic method:

estimation of relevant physiological parameters”,

Development of Instant Measuring Model for Oxygen Permeability and Water Content of Hydrogel Contact Lens

181

Industrial & Engineering Chemistry Research, 47, 10,

3619-3629.

Compañ, V., Andrio, A., López-Alemany, A., Riande, E.,

Refojo, M. F., 2002. “Oxygen Permeability of

Hydrogel Contact Lenses with Organosilicon Moieties”,

Biomaterials, 23, 2767-2772.

ISO International Standard 9913-1: 1996. Optics and

optical instruments, Determination of Oxygen

Permeability and Transmissibility by the Fatt Method.

Geneva, Switzerland: International Organization for

Standardization.

ISO International Standard 9913-2: 2000. Optics and

optical instruments, Determination of Oxygen

Permeability and Transmissibility by the Coulometric

Method. Geneva, Switzerland: International

Organization for Standardization.

ISO International Standard 18369-3: 2006. Ophthalmic

optics-Contact lenses. Part 3: Measurement methods.

Geneva: International Organization for Standardization.

Oberndorf, D., Wilhelm, M., 2003. “Determination of

oxygen permeability/transmissibility and storage of

contact lenses using HPLC with reductive

electrochemical detection in combination with

speciﬁcally designed sampling unit”, Anal. Chem. 75,

1374–1381.

Hadassah, J., Sehgal, P. K., 2006. “A novel method to

measure oxygen permeability and transmissibility of

contact lenses”, Clin. Exp. Optom., 89, 6, 374-380.

Hale, G. M., Querry, M. R., 1973, “Optical constants of

water in the 200nm to 200µm wavelength region”, Appl.

Opt., 12, 555-563.

Prahl, S., 2009, “Optical Absorption of Water”, Optical

Spectra, http://omlc.org/index.html.

Taiz, L., Zieger, E., 2015. Plant Physiology and

Development, Sinauer Associates, Inc.6th edition.

PHOTOPTICS 2017 - 5th International Conference on Photonics, Optics and Laser Technology

182