A C T A O P H T H A L M O L O G I C A V O L . 5 8 1 9 8 0

Department of Ophth.almolo~gyl (Head: N. Ehlers), Department ?f Nuclpnr M e d i k e , RndizimrentrPz (Head: H . Hvid Hansen)

Arhiu Kotnmiinrhopital, Universitji ?f Anrliw, and Synoptik3, Arhus Denmark

TEAR FLOW AND SOFT CONTACT LENSES

BY

T. S0RENSENl F. TAAGEHOJZ and ULRICH CHRISTENSEN3

Tear flow was determined in 14 persons before and after one month of adaptation to a soft contact lens, (SoflenP, Bausch & Lomb), by means of a radioactive tracer (technetium, Tc5'Qm, as pertechnetate), a gamma camera and a computer system. The elimination of the radioisotope from the conjunctiva1 sac was diphasic with a significant increase of the fractional turnover rate after the adaptation period in the initial phase with a rapid elimination, but no change in the basal phase with a slower elimination. The fractional turnover rate was also determined with the soft contact lens placed on the cornea after having been pre-soaked in the technetium solution resulting in a value of 0.02 1 i 0.003 min-' (mean k SEM, n = 12). The fractional turnover rate resulting from instillation of the radioisotope on the non-pre-soaked soft contact lens placed in the eye was found to 0.020 i 0.004 min-1 (mean k SEM, n = 6). In the studies with the soft contact lens in the eye the elimination curves was monophasic and not diphasic as in normal tear flow studies.

Key words: tear flow - technetium - gamma camera - soft contact lenses - human.

In fitting guides for soft contact lenses it is often reckoned that tear deficient eyes are a relative contraindication for contact lens wear. On the other hand several authors have reported the results of treatment of dry eyes with soft contact lenses.

A stimulation to the normal human eye will result in an increased tear flow for a few min. In the adaptation period to a contact lens the patients often experience watery eyes for some time. The gradual return to normal conditions could be explained by a 'fatigue block as described by Jones (1966). In patients fitted with hard contact lenses the decrease in corneal sensitivity could be responsible for the

Received October 30, 1979.

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Tear flow and soft contact lenses

normalization of lacrimation in the adaptation period, whereas this can not be the explanation with soft contact lenses causing almost no changes in corneal sensitivity (Millodot 1974, 1976).

The purpose of this paper was to study the possible effect of a well adapted soft contact lens on tear flow determined by means of a radioactive tracer and a dynamic gamma camera detection system with and without the soft contact lens placed on the human eye.

Material

The material comprised 18 human volunteers - 4 males and 14 females - in the age group 20 to 30 years. They were fitted with Soflens@ (Bausch & Lomb) according to the manufacturer's fitting schedule. All the volunteers were myopic (range -1.50 to -5.25 dioptres) except one with a low grade of hypermetropia. The patients were checked by slit lamp microscopy, ophthalmoscopy and keratometry. Vital staining with Rose Bengal and fluorescein was carried out to exclude persons with corneal abnormalities. Tear break up time was found normal (over 20 seconds). Most of the volunteers joined the group of persons comprising the material of normal persons in a tear flow study (Sorensen & Taagehoj Jensen 1979). Four of the patients only joined the fourth determination.

Counts / 10 sec. ( log scale 1

500 - 400 - 300 -

200 -

100 -

6 0 ' I I I I I I I , I , 1 I I , 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Min

Fzg. 1. Tear flow curve from a normal person without contact lenses with an initial phase from 2-6

min and a basal phase from 7.5-15 min after instillation.

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T. S@rnsen, F. Taageh#i Jensen and Ulrich Christensrn

Method

The method has been described in detail in another paper (SGrensen & Taagehej Jensen 1977, 1979). The parameter for tear flow, the fractional turnover rate, was calculated from the elimination curves of the radioisotope (technetium, Tc99m, as pertechnetate) from the conjunctival sac. The patients were placed in the supine position with the head fixed under the pinhole collimator in the gamma camera. A volume of 10 pl of a normal saline solution with the technetium was instilled on the center of the cornea (dose 100-200 pCi). The fractional turnover rate (Fig. 1) was calculated in the initial phase (approximately 2-5 min after instillation) and in the basel phase (7.5-15 min after instillation). Four determinations were carried out in the same eye: 2 before the fitting of the soft contact lens and one after an adaptation period of at least 3 weeks. This third determination was carried out without a soft lens on the eye immediately after removal of the lens, but with a soft lens on the fellow eye. In the fourth measurement the contact lens was placed in the eye during the recordings. In 12 of these determinations with the soft lens on the eye the lens was pre-soaked in a 10 fold diluted technetium solution for 20 min before the recordings, whereas 6 of the studies were carried out by instillation of the undiluted radioisotope solution on the soft contact lens placed on the cornea.

All tear flow determinations were corrected for background radiation as described in a previous paper (Sorensen & Taagehej Jensen 1979).

Results

The second determination before adaptation was compared to the determination after adaptation (in 2 cases the first determination was used because the second determination failed). As shown in Table I the mean fractional turnover rate in the initial phase was found to be higher after adaptation (t-test for paired data: 2P =

2.5-5%), whereas the basal fractional turnover rate was of the same magnitude after adaptation (t-test for paired data: 2P = 20-3076). The elimination curves before and after adaptation were all diphasic in a semilogarithmic plot.

When a pre-soaked soft contact lens was placed on the eye, the radioactivity could be seen accumulated corresponding to the position of the soft lens on the cornea (Fig. 2) with some radioactivity entering the lacrimal pathway. A similar distribution was seen when a non-pre-soaked lens was placed on the cornea followed by an instillation of 10 pl technetium solution directly on the soft contact lens. Relatively small amounts of radioactivity was seen in the conjunctival sac outside the soft lens in both cases.

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Tear f low and soft contact lenses

Table I . Fractional turnover rate before and after adaptation to a soft contact lens and fractional turnover rates representing the elimination of

technetium from soft lenses. (mean _+ SEM).

I Initial I Basal

Before adaptation 0.173 + 0.015 0.076 k 0.006 (second determination (min-1) (min-1) (n = 14)

After adaptation 0.204 2 0.014 0.069 * 0.006 (third determination (min-1) (min-1) (n = 14)

Soft contact lens pre-soaked in diluted technetium solution (min-1) (n = 12)

Soft contact lens placed on thecornea during instillation of technetium (min-1) (n = 06)

0.021 2 0.003

0.020 k 0.004

With the soft lens placed on the cornea, whether pre-soaked or not pre-soaked, the elimination curves turned out to monophasic in the similogarithmic plot (Fig. 3). T h e fractional turnover rate was 3-4 times smaller than in the basal phases in tear flow studies without a contact lens in the eye. The difference between the pre-soaked and non-pre-soaked group was not statistically significant.

Discussion

A persistent irritation to the conjunctiva has been said to provoke a ’fatigue block’, which is thought to be a block in the efferent nerves to conjunctival sensory impulses (‘Jones 1966). Whether a ‘fatigue block’ can be caused by a contact lens seems not to be known though the assumption is obvious.

This study showed that the tear flow was not decreased by the adaptation to a soft contact lens. Thus a reduced tear secretion cannot be regarded as a cofactor in the development of deposits on soft contact lenses in normal persons. On the contrary a tendency to a small increase in the initial tear flow was found.

T h e elimination curves with the soft contact lens placed on the cornea were monophasic with an elimination of approximately 2 %/min. This slow monophasic

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T. Sdwnren, F. Tuugeh#l JenAen and Ulrzch Chnstensen

Fig. 2. T h e distribution of technetium in an eye fitted with a soft contact lens. The radioactivity is accumulated in the lens. Radioactivity is also seen in the lacrimal pathways. Three scintigrams

with different degree of exposure are shown. Some radioactivity has entered the nose.

COUNTS/10 SEC.

k = 0.019 f .. . .-.*... .....*...... -.. -:.. ..* ..... * ..

... ... 3000 -.- .. -.....:. - .. .'-. .._. 2000 j

1 MIN. , I , , I I 2 4 6 8 10 12 14 16

I

Fig. ?. Elimination of technetium from a soft contact lens on a human eye. Radioactivity from the conjunctival sac area including the soft lens plotted versus time in a semilogarithmic system.

Each dot represents a recording in a ten second interval.

186

Teur flozu and soft contact lense,

elimination was not a result of a fatigue block, because the elimination curves in persons wearing hard lenses have a diphasic shape like the curves in normal persons without contact lenses (personal observation to be published later). The explanation can be that the negatively loaded pertechnetate was accumulated in the soft contact lens and that the elimination curves represented the elimination of the radioisotope from the contact lens material. The monophasic shape suggested that the elimination curve was dominated by the elimination from the lens making the elimination from the conjunctival sac invisible.

In the pre-soaked and non-pre-soaked lenses were found fractional turnover rates of the same magnitude. This means that the technetium after uptake by the lens has been bound in the lens material in a way resulting in an elimination, of 2 %/min when the lens was placed on a human eye.

These results add to the interest of the soft contact lens-drug relationship. It seems obvious that some drugs will be retained in the lens material in the similar way as technetium with prolonged corneal contact times. However, the elimination of most drugs from soft materials during in vivo conditions is unknown and probably depends on the chemical binding between the drug and the lens material.

Acknowledgment

The study was supported by the Bausch & Lomb Company.

References

Jones L. T. (1966) The lacrimal secretory system and its treatment. Ampr. J . Ophthal. 62, 47-60.

Millodot M. (1974) Effect of soft lenses on corneal sensitivity. Acta ophthal. (Kbh.) 52, 603-608.

Millodot M. (1976) Effect of the lenght of wear of contact lenses on corneal sensitivity. Acta

SGrensen T. & Jensen F. T. (1977) Methodological aspects of tear flow determination by

SGrensen T. & Jensen F. T. (1979) Tear flow in normal human eyes. Determination by means

ophthal. (Kbh.) 54,72 1-730.

means of a radioactive tracer. Acta ophthal. (Kbh.) 55, 726-738.

of radioisotope and gamma camera. Acta ophthal. (Kbh.) 57, 564-581.

Author’s addrrss: Torben SGrensen, Department of Ophthalmology, Arhus Kommunehospital, DK-8000 i\rhus C, Denmark

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