British Joumnal of Ophthalmology 1995; 79: 1007-101 1

Sodium hyaluronate eyedrops in the treatment ofdry eyes

Shigeto Shimmura, Masafumi Ono, Kazumi Shinozaki, Ikuko Toda, Etsuko Takamura,Yukihiko Mashima, Kazuo Tsubota

AbstractBackground-Several studies in the pasthave attempted to demonstrate theefficacy of sodium hyaluronate in thetreatment of dry eyes. However, resultshave been conflicting and a definite con-clusion has not yet been reached. Thisstudy recruited a larger group of patientsand has incorporated for the first timeboth fluorescein and rose bengal stainingin the evaluation ofthe epithelium.Methods-Eighteen albino rabbit corneaswere used in a basic animal study todemonstrate the efficacy of sodiumhyaluronate by comparing the effects onthe rate of epithelial healing. The optimalconcentration to be used in the clinicaltrial was determined from the results ofthe basic study. In the clinical study 104patients with dry eye syndrome wereenrolled in a double masked controlledclinical trial. Patients received sodiumhyaluronate drops in one eye and controlmedication in the other eye for 4 weeks.Grading of subjective symptoms andclinical exmnations were performed at 2and 4 weeks.Results-In the animal study sodiumhyaluronate at concentrations of 0-1%and 0*5% significantly accelerated therecovery time of iodine vapour inducedcorneal erosions (p< 0-01). In the clinicalstudy no statistical significance wasobserved in the improvement ofsubjectivesymptoms or rose bengal staining, whilefluorescein scores significantly improvedin eyes receiving sodium hyaluronate(p=0.0001) at 4 weeks.Conclusion-Sodium hyaluronate dropsapplied in six daily doses could not bedemonstrated to offer advantages overconventional tear supplies in the improve-ment of subjective symptoms, but mayplay a role in maintaining a healthycorneal epithelium.(Br_J Ophthalmol 1995; 79: 1007-101 1)

Sodium hyaluronate is a glycosaminoglycanfound in significant amounts in synovial fluidand the vitreous humour. Owing to the largenumber of negative charges on the molecule,sodium hyaluronate is capable of holding largequantities of water, and thus lubricatingsurrounding structures. Previous studies haveevaluated the efficacy of sodium hyaluronate asa tear replacement in the treatment of dry eyeswith varying results.' Controlled doublemasked studies by Limberg4 and Nelson5

showed no significant advantage comparedwith chondroitin sulphate or polyvinyl alcohol,while Sand6 concluded that sodium hya-luronate was effective in another doublemasked trial. This discrepancy may be due tofactors such as differences in severity of dryeyes, variation of examination techniques, orfrequency of application. The relatively smallnumber of patients enrolled (20 to 30 cases ineach study) may have contributed to statisticalvariation. However, certain properties ofsodium hyaluronate such as long ocularsurface residence time7 and increased tearevaporation from the ocular surface followingapplication8 make sodium hyaluronate apromising agent that merits a more extensivestudy.

In order to provide additional evidence forthe effectiveness of sodium hyaluronate, wefirst conducted an in vivo study using rabbitsto demonstrate the effects of sodiumhyaluronate on experimentally induced cornealepithelial lesions, followed by a multicentred,controlled double masked clinical trial ofsodium hyaluronate in the treatment of kerato-conjunctival lesions in dry eyes. We adopted astudy design in which sodium hyaluronate andplacebo were applied concurrently in differenteyes of the same patient in order to minimisedifferences in study conditions. This minimisestemporal factors that come into play whencomparing eyedrops applied during differenttime periods.

This study focused primarily on fluoresceinstaining as well as rose bengal staining. Bothfluorescein and rose bengal are of the hydroxy-xanthene dye family, with rose bengal havingextra halide derivatives within the moleculeaccounting for its larger molecular weight andshift in spectroscopic absorption wavelength.Feenstra and Tseng9 reviewed how fluoresceinand rose bengal have slightly different stainingproperties. Although the consensus is that rosebengal stains non-viable cells and mucousstrands, it has been demonstrated to stainviable cells in vitro but, in vivo, is blocked bytear component proteins and polymers such ascarboxymethylcellulose. On the other hand,fluorescein lacks this ability to be blocked bytear constituents, and diffuses rapidly into thestroma where cell to cell junctions are dis-rupted. The clinical implications of each dye,as summarised by Feenstra and Tseng, are thatfluorescein staining is promoted by disruptionof cell-cell junctions, and rose bengal stainingis due to insufficient protection of the pre-ocular tear film, both in terms ofdecreased tearcomponents and abnormal surface epithelialcells. The different staining properties of each

Department ofOphthalmology, KeioUniversity School ofMedicine, Tokyo,JapanS ShimmuraY Mashima

Department ofOphthalmology,Minami-TamaHospital, Tokyo, JapanM Ono

Department ofOphthalmology, TokyoWomen's MedicalCollege,Tokyo, JapanK ShinozakiE Takamura

Department ofOphthalmology, TokyoDental College, Chiba,JapanI TodaK Tsubota

Correspondence to:Shigeto Shimmura, MD,Department ofOphthalmology, KeioUniversity School ofMedicine, Shinanomachi 35,Shinjuku, Tokyo, Japan.Accepted for publication18 July 1995

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dye may prove effective in differentiating thepathological condition of the corneal epithe-lium. Micropipettes were used to apply fluo-rescein and rose bengal in order to standardisethe amount of applied dye as much as possible.

Material and methods

BASIC STUDYEighteen corneas of nine male albino rabbitsweighing 2 to 3 kg were used in the study. Testmedication consisted of 01% and 05%sodium hyaluronate, while the vehicle of thesolution (phosphate buffer, pH 7 35) servedas a control. Corneas were divided into fourgroups: two groups receiving sodiumhyaluronate in concentrations mentionedabove (n=4 and 5 respectively), one groupreceiving the vehicle (n=4) serving as control,and one untreated group (n= 5).

Corneal erosions were made according toParkinson and Schuchard10 using iodinevapour. In brief, rabbits were put undergeneral anaesthesia by pentobarbitone fol-lowed by topical administration of oxybupro-caine. A 7 mm glass tube with a glass wool plugcontaining iodine crystals was gently applied tothe central cornea for 3-5 minutes. Roundcorneal erosions appeared approximately 4hours after exposure to iodine vapour.

Corneas were stained with fluorescein, andthe area of epithelial erosions was quantita-tively calculated using a digitiser (Cosmozone1S, Nikon Inc, Tokyo, Japan). After initialevaluation at 4 hours, 50 ,ll of 0 1%, 0 5%sodium hyaluronate, and control were appliedfour times daily at 2 hour intervals for 2 days.Evaluation of the wounded cornea was done at22, 28, and 34 hours. Statistical analysis was

performed by the one way ANOVA andDuncan's tests.

CLINICAL STUDYThe clinical study was conducted at eight majormedical centres by 18 dry eye specialists duringa period of 9 months between September 1991to May 1992. A total of 104 patients with dryeye syndrome (including Sjogren's syndrome)were enrolled. Dry eye was diagnosed accord-ing to Toda et al." In brief, patients with (1)dry eye related symptoms, (2) positive stainingwith either fluorescein or rose bengal, and (3)tear break up time less than 5 seconds or aSchirmer test value of less than 5 mm were

diagnosed as having dry eyes. Sjogren's syn-drome was diagnosed according to the criteriaproposed by Fox et al, 12 where patients positivein three or more of the following four criteriawere diagnosed as having Sjogren's syndrome:(1) dry eye, ( 2) xerostomia, (3) lymphocyticinfiltrates on minor salivary gland biopsy, and

(4) serological evidence (positive rheumatoidfactor or positive antinuclear antibody or posi-tive SS-A or SS-B antibody). The criteria fordry eye in this case are somewhat different fromthe original criteria for keratoconjunctivitissicca (KCS) proposed by Fox et al on twopoints: (1) the presence of symptoms is not

questioned in the original paper, and (2)patients with Schirmer values in the normalrange, but with tear break up times of less than5 seconds were included.

All patients gave their informed consentbefore enlisting in the study. In addition to thediagnosis of dry eye, patients eligible for thestudy were required to have a rose bengal scoreof greater than 3 (on a scale of 0 to 21). Thiswas to exclude very mild cases where statisticalcomparisons of staining scores would not bepossible. Patients with infectious extraoculardisease, corneal epithelial disorders associatedwith diabetes mellitus, and neurotrophic ker-atitis were excluded from the study. Patientswith overt asymmetrical staining patterns atthe time of initial examination were alsoexcluded.The test medication used was a preservative-

free 0 1% sodium hyaluronate solution (1 X 106Da) bottled in a single dose disposable con-tainer. The vehicle for the solution, consistingof the same agents as the test solution exclud-ing sodium hyaluronate (25 mM phosphatebuffered saline, pH 7 36), was used as control.Identical disposable containers were usedso that discrimination between solutions wasdifficult.The study was conducted in a double blind,

controlled fashion in which each patientreceived the sodium hyaluronate eyedrops inone eye, and the vehicle in the other. The eyeto receive sodium hyaluronate in each patientwas randomly selected by a designated studycontroller.

Before participating in the study, patientswere required to 'wash out' their eyes for 2weeks with a conventional preservative-freeartificial tear solution (Soft Santear, an iso-tonic NaCl, KCI solution with 1% boric acid,pH 7-0-8-0, Santen Pharmaceuticals, OsakaJapan), applied six times a day. After this 2week period, patients were examined andinterviewed to grade subjective symptomssuch as foreign body sensation, pain, burning,and itching on a scale of 0 to 5 (see Table 1 forlist of symptoms). Fluorescein and rose bengalstaining, as well as tear break up time wereobserved according to Toda and Tsubotal3 byinstilling 2 ,ul of a 1% fluorescein-1% rose ben-gal solution by micropipette (Fig 1).Micropipettes were used in order to obtain

Table 1 Improvement in symptoms (SD) in 91 patientsafter 4 weeks

0 1% Sodiumhyaluronate Control

Asthenopia -0 55 (0 90) -0-46 (0 89)Dry eye sensation -0-69 (1-04) -0-65 (1-16)Foreign body sensation -0-67 (1.10) -0-56 (1-07)Pain -0-40 (1-00) -0-41 (1 10)Blurred vision -0 43 (0 80)* -0 30 (0 84)Photophobia -0 34 (0 82) -0-31 (0 85)Redness -0 43 (0 99) -0-52 (1-02)Discharge--0-24 (0 81) -014 (080)Heavy lids -0-40 (1-06) -0 35 (0 98)General discomfort -0 59 (1-14) -0-46 (1-10)Difficulty in awakening -0-14 (0 85) -0-13 (0-79)Epiphora -0-10 (0 62) -0 07 (0 44)Itchy sensation -0-04 (0-82) +0 01 (0-81)Hot sensation -0-08 (0-97) -0 03 (0 90)

Minus sign indicates decrease (improvement) in grading score.*p=0-0627 (Wilcoxon's signed rank test), p>0 1 for all otherexaminations.

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Figure 1 Slit-lamp photograph folowing application of2 ,ul of %fluorescein-1% rosebengal solution by micropipette.

consistent volumes and concentrations of dyeso that staining scores were not influenced bythe staining habits of different physicians.Staining was graded on a scale of 0 to 3 foreach section of cornea and conjunctiva as inFigure 2, followed by a photograph and/ordetailed sketch. Comeal debris, meibomitis,conjunctivitis, and conjunctival injection were

graded on a scale of 0 to 4. Schirmer test andtear clearance were observed simultaneouslyaccording to Ono et al,4 5 minutes after instil-ling 10 [lI of a 0-5% fluorescein-0-1% oxy-

buprocaine solution by micropipette. Tearclearance was evaluated by the colour of theSchirmer strip stained by residual fluoresceinin the conjunctival sac. Schirmer strips stainedwith known concentrations of fluorescein were

compared with the Schirmer strip of thepatient to determine qualitatively the amountof fluorescein remaining after 5 minutes. TheSchirmer test with nasal stimulationl5 was per-formed on selected patients. Following prelim-inary examinations, patients were suppliedwith two sets of eyedrops in single use dispos-able containers with labels indicating the eye tobe treated. Neither the patient nor the physi-cian knew of the contents. Information con-

cerning which eye to receive sodiumhyaluronate and which eye to receive control in

Rose bengal staining Fluorescein stainingFigure 2 Anterior segment sectioningfor staining scores. Each compartment was graded ona scale of 0 (no staining) to 3 (intense staining). Rose bengal: (1) superior palpebralconjunctiva, (2) and (6) nasal and temporal bulbar conjunctiva, (3) superior cornea,(4) mid cornea, (5) infenor cornea, (7) inferor palpebral conjunctiva. Fluorescein:(1) superior cornea, (2) mid cornea, (3) inferior cornea.

each patient was sealed in an envelope, keptunder guard by the study controller, and leftunopened until the study was over. Patientswere asked to use the designated eyedrops ineach eye six times daily at 3 hour intervals for 4weeks. Patients were equipped with digitalwrist watches with preset alarms indicatingtime of eyedrop application. Compliance wasdetermined by counting the number of emptycontainers collected upon each visit. Gradingof subjective symptoms and objective findingswas repeated at 2 weeks and at the end of thestudy.

Wilcoxon's signed rank test was used toanalyse differences in efficacy between eachtest medication. Analysis was done in theentire group as a whole, and in subgroups ofpatients with the Sjogren's syndrome andpatients with non-Sjogren dry eye.'6

Results

BASIC STUDYEach group demonstrated a linear reduction inerosion size as shown in Figure 3. The timerequired for 50% recovery in erosion size wassignificantly shorter in groups receiving 01%and 0 5°/ sodium hyaluronate (18 hours) com-pared with the untreated group, or the groupreceiving vehicle alone (30 hours). The accel-erating effect of sodium hyaluronate wasobserved up to 22 hours after erosion of theepithelium. Between 22 hours and 34 hours,the healing rates in each group were similar,but wound area was significantly smaller inboth concentrations of sodium hyaluronatecompared with control and the untreatedgroup. No significant difference was observedbetween 0-1% and 0 5% sodium hyaluronatein both healing rate and wound area, andtherefore 01% was chosen as the final con-centration to be used in the clinical trial.

CLINICAL STUDYOf the 104 patients enrolled in the study, 91patients successfully completed the trial andwere eligible for statistical analysis. Among the13 dropout patients, two patients developedsigns of allergic conjunctivitis, one discon-tinued treatment because of exacerbation ofsymptoms, and the remainder were disquali-fied because of non-compliance of dose orperiod not related to symptoms or side effects.Non-compliance was mainly the result of alack of understanding of the protocol such asomitting to apply drops, or failure to visitclinics on the appointed dates. Compliance ofdose was confirmed by counting the number ofempty and untouched containers collected ateach visit.No statistically significant difference was

observed between any of the subjective symp-toms under study in terms of improvement ingrading scores (Table 1). There was a trendtowards improvement in blurring of vision ineyes receiving sodium hyaluronate (p=0.063).The absolute score value for foreign bodysensation at 4 weeks was less in sodium

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N 40

E 0*O5%HA=30L20

0

4 22 28 34Time following exposure to iodine vapour

(hours)Figure 3 Wound size (mean (SD)) folowing application ofsodium hyaluronate drops and controL Wound sizeimproved significantly earlier in groups receiving 0 1% and05% sodium hyaluronate. No signifcant difference wasobserved between each concentration ofsodiumhyaluronate. HA=sodium hyaluromate.

hyaluronate treated eyes in the Sjogren group(1-67 (SD 0.20) versus 1-97 (SD 0-21)) andthe entire group (1'20 (SD 0-12) versus 1X36(SD 0d13)) with statistical significance; how-ever, when comparing improvement (differ-ence in score before and after treatment) thedifference was not significant. Neither of thetest medications was overwhelmingly preferredover the other in a questionnaire completed byparticipants at the end of the study.

Fluorescein staining scores significantlydecreased in eyes receiving sodiumhyaluronate (average decrease 1 46 (SD 2 08))compared with eyes receiving control at 4weeks (average decrease 0 54 (SD 1-89))(p=0.0001). No statistically significant differ-ence was observed in rose bengal staining, tearbreak up time, Schirmer scores, or tear clear-ance. Similar results were obtained in both theSjogren group and the non-Sjogren dry eyegroup when analysed separately (Table 2).

DiscussionAlthough previous studies have demonstratedgreater subjective improvements in eyes receiv-ing sodium hyaluronate drops, our study failedto demonstrate any significant difference com-pared with the control except for a trend inimprovement in blurred vision and foreignbody sensation. The grading scores for symp-toms improved in both eyes in the majority ofcases. This may be due to the therapeuticeffects of the placebo vehicle itself, as well asthe difficulty patients may have experienced ingrading symptoms in each eye separately. Inother words, symptomatic relief or deteriora-tion in one eye invariably affected judgment ofsymptoms in the other eye. The use of a fivepoint scale for symptoms as well as the long list

Table 2 Improvement in staining score (SD) after 4 weeks

No ofpatients Stain 0-1% HA Control p Value

Total 91 Rosebengal -1-27(1-84) -1 19 (209) 0-8955Fluorescein -1-46 (2 08) -0 54 (1-89) 0-0001

Non-Sj6gren's Rose bengal -1-36 (1-77) -1-49 (2 08) 0-6926syndrome 55 Fluorescein -1-40 (2 29) -0-58 (2 08) 0 0049

Sj6gren's Rose bengal -1-14 (1-97) -0-72 (2 05) 0-5643syndrome 36 Fluorescein -1-56 (1-73) -0 47 (1-58) 0-0005

HA=sodium hyaluronate. Minus sign indicates decrease in staining score. Statistical analysis byWilcoxon's signed rank test.

of relatively non-specific symptoms understudy may have been an excess burden for thepatients, which may have affected their con-centration and keenness. The trends observedin the study suggest that a more extensivestudy focusing on fewer symptoms may beworthwhile.To our surprise, fluorescein staining scores

significantly improved in eyes receiving sodiumhyaluronate drops, while no significant differ-ence was observed in rose bengal scores. Basedon the observations made by Feenstra andTseng9 as reviewed in the introduction to thispaper, the lack of improvement in rose bengalscores suggests that sodium hyaluronate drdpsin quantities used in the study (six drops perday) may not be sufficient to stabilise the pre-ocular tear film. The half life of 0-2% sodiumhyaluronate applied to the ocular surface isreported to be approximately 321 seconds,7and thus a more frequent dose may be moreeffective. However, the improvement in fluo-rescein scores indicates that sodiumhyaluronate may improve cell to cell adhesionsbetween corneal epithelial cells, since fluores-cein staining is exaggerated by rapid diffusioninto the stroma through disruptions in cell tocell junctions.9

Pflugfelder et al 17 have suggested the possi-bility that squamous metaplasia of the con-junctiva in patients with Sjogren's syndromemay be a primary feature of the disease in addi-tion to tear deficiency. The fact that sodiumhyaluronate in six daily doses improved fluo-rescein scores in the Sjogren group may be apromising sign that sodium hyaluronate can beused to treat conditions caused by factors otherthan desiccation.

Results of the preliminary study on rabbitsalso confirmed that sodium hyaluronate dropshave an accelerating effect on epithelial woundhealing in vivo. The mechanism by whichsodium hyaluronate enhances epithelial woundhealing has not yet been clarified. Fibronectin isknown to promote epithelial wound healingby chemotactic and haptotactic effects onepithelial cells.1820 Inoue and Katakami2lreported that sodium hyaluronate promotes cellproliferation, which may contribute to thewound healing effects of sodium hyaluronate.Nishida et al 22have demonstrated that sodiumhyaluronate stimulates comeal epithelial migra-tion in rabbit organ cultures, which was notaffected by the addition of antisera againstfibronectin or epithelial growth factor. Theeffects ofsodium hyaluronate on the epitheliummay be caused by different factors from thoseof fibronectin and epithelial growth factor. Thepossible existence of sodium hyaluronate bind-ing sites in the epithelium has been suggested.22

Previous reports have demonstratedimprovements in rose bengal staining with theuse of sodium hyaluronate drops.2 5 6 This dis-crepancy with our results may be due to differ-ences in scoring methods, the manner in whichdyes were applied, or the number of patientsinvolved. Certain limitations in our studydesign can also be pointed out. Differentclimatic conditions among the eight centresmay have contributed to variability. Although

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outpatient clinics were all run during themorning, variation in the interval betweenclinical evaluation and the last drop appliedmay have affected results. However, the rela-tively large number of patients (n= 104)enrolled in this double blind study, excellentpatient compliance, and the use ofmicropipettes to apply precise amounts of dyehave assured maximal standardisation in sucha clinical situation.Sodium hyaluronate drops presented with

very few complications. Two patients devel-oped signs of allergic conjunctivitis, and onlyone patient had to discontinue the trial owingto exacerbation of symptoms. This patientwas treated with her original prescription offrequently applied tear supplies to alleviatesymptoms.Sodium hyaluronate drops alone in six daily

doses may not adequately improve subjectivesymptoms associated with dry eye, but mayplay a role in maintaining a healthy cornealepithelium. Drops applied more frequently, orin conjunction with conventional tear replace-ments, may offer effective treatment ofpatients with dry eyes.

1 Polack FM, McNiece MT. The treatment of dry eyes withNa hyaluronate (Healon). Cornea 1982; 1: 133-6.

2 DeLuise VP, Peterson WS. The use of topical Healon tearsin the management of refractory dry eye syndrome.Ann Ophthalmol 1984; 16: 823-4.

3 Mengher LS, Pandher KS, Bron AJ, Davey CC. Effect ofsodium hyaluronate (0-1%) on break-up time (NIBUT)in patients with dry eyes. Br J Ophthalmol 1986; 70:442-7.

4 Limberg MB, McCaa C, Kissling GE, Kaufman HE.Topical application of hyaluronic acid and chondroitin

sulfate in the treatment of dry eyes. Am J Ophthalmol1987; 103: 194-7.

5 Nelson JD, Farris RL. Sodium hyaluronate and polyvinylalcohol artificial tear preparations. Arch Ophthalmol 1988;106: 484-7.

6 Sand BB, Marner K, Norn MS. Sodium hyaluronate in thetreatment of keratoconjunctivitis sicca. Acta Ophthalmol1989; 67: 181-3.

7 Snibson GR, Greaves JL, Soper NDW, Tiffany JM, WilsonCG, Bron AJ. Ocular surface residence times of artificialtear solutions. Cornea 1992; 4: 288-93.

8 Tsubota K, Yamada M. Tear evaporation from the ocularsurface. Invest Ophthalmol Vis SCi 1992; 33: 2942-50.

9 Feenstra RPG, Tseng SCG. Comparison of fluorescein androse bengal staining. Ophthalmology 1992; 99: 605-17.

10 Parkinson G, Schuchard R. A standard large wound of thecorneal epithelium in the rabbit. Invest Ophthalmol Vis Sci1979; 18: 103-6.

11 Toda I, Fujishima H, Tsubota K. Ocular fatigue is themajor symptom of dry eye. Acta Ophthalmol 1993; 71:347-52.

12 Fox R, Robinson C, Curd J, Kozin F, Howell F. Sjogren'ssyndrome: proposed criteria for classification. ArthritisRheum 1986; 29: 577-83.

13 Toda I, Tsubota K. Practical double vital staining for ocularsurface evaluation. Cornea 1993; 12: 366-8.

14 Ono M, Tsubota K, Yoshino K, Yamada M. Tear fluidclearance test. _pn J Clin Ophthalmol 1991; 45: 1143-7.

15 Tsubota K. The importance of the Schirmer test with nasalstimulation. AmJ Ophthalmol 1991; 111: 106-108.

16 Tsubota K, Toda I, Yagi Y, Ogawa Y, Ono M, Yoshino K.Three different types of dry eye. Cornea 1994; 13: 202-9.

17 Pflugfelder SC, Huang AJW, Feuer W, Chuchovski PT,Pereira IC, Tseng SCG. Conjunctival cytologic featuresof primary Sjogren's syndrome. Ophthalmology 1990; 97:985-91.

18 Nishida T, Nakagawa S, Awata T, Ohashi Y, Watanabe K,Manabe R. Fibronectin promotes epithelial migration ofcultured rabbit cornea in situ. J Cell Biol 1983; 97:1653-7.

19 Nishida T, Nakagawa S, Nishibayashi C, Tanaka H,Manabe R. Fibronectin enhancement of corneal epithelialwound healing of rabbits in vivo. Arch Ophthalmol 1984;102: 455-6.

20 Watanabe K, Nakagawa S, Nishida T. Chemotactic andhaptotactic activities of fibronectin for cultured rabbitcorneal epithelial cells. Invest Ophthalmol Vis Sci 1988; 29:572-7.

21 Inoue M, Katakami C. The effect of hyaluronic acid oncorneal epithelial cell proliferation. Invest Ophthalmol VisSci 1993; 34: 2313-5.

22 Nishida T, Nakamura M, Mishima H, Otori T. Hyaluronanstimulates corneal epithelial migration. Exp Eye Res 1991;53: 753-8.

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