F I.

USAFSAMTR85-25

HARD-COATED POLYCAR6ONATE VERSUS CR-39 LENSES: a'

A Field Study *

0 '

J. W. MillerWayPe F. Provines, Lieutenant Colonel, USAF, BSCAlton J. Rahe, M.S.Roger H. Blevins, Staff Sergeant, USAFThomas J. Tredici, Colonel, USAF, MC

May 1985

Final Report for Period October 1981 - September 1982

fApproved for public release; distribution is uninl-ted.J

USAF SCHOOL OF AEROSPACE MEDICINE a.:..Aerospace Medical Division (AFSC)

.,",aaQ:.aa.Brooks Air Force Base, TX 78235-5J01

85 6 19 020 0___________.__ -_

NOTICES

This final repurt was submitted by personnel of the Ophthalmology Branch,Clinical Sciences Division, and the Data Sciences Division, USAF School of PAerospace Medicine, Aerospace Medical Division, AFSC, Brooks Air Force Base,Texas, under job order 7755-24-06.

Whan Government drawingst specificatio'is, or other data are used for anypurpose other than in connaction with a deflnAtely Goverinentrelated procure= -"

meet, the United States Government incurs no responsibility nor any obligation Awhatsoever, The fact that the Government may have formulated or in any waysupplied the said drawings, specifications, or other data, is not to be 7regarded by implication, or otherwise in any manner construed, as licensing theholder, or any other person or corporation; or as conveying any rights orpermission to manufacture, use, or sell any patented invention that may in anyway be related thereto. 5

The Office of Public Affairs has reviewed this report, and it is releasableto the National Technical Information Service, where it will be available to thegeneral public, including foreign nationals.

This report has been reviewed and is approved for publication. •J. W. MILLER 7.1OHAS J. TRED , Colonel, USAF, MCProject Scientist Supervisor

ROYCE MOSER, Jr.

Colonel, USAF, MCCommander

"- -"--0- '

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, i Y -.... 4...

"' Spca

4'-: ;

?ICIIASSIFIED -

siT~t'trv CLASSIFICATION OF THIS PAGE

REPORT DOCUMENTATION PAGEA.APO)RI SECURITY CLASSIFICATION III, 14CSTRICTIVE MARK~INGS

2.. SIECUMIYY CLASSIFICATION AUTHO0RITY 3, DIST 91 UT IONIAVAI LAS ILITY OF REPORT

~. OCLA8I~t~TO~gowNOA~iO ~Approved for public release; distribuLionis unliited.

A P1 RFORMING ORIGANIZATION REPOCRT NUMBHRIS1 5 MONITORING ORGANIZATION RLPOIIT NUM111981S

TJSAFSAM-TR-85-25A _ _ _ _ _ __ __6_ _ __ _ _ _ _ _ _

G& NAME OF PERFORMING ORGANIZATION 15. OFFICE SYMO 7a, NAME OF MONITORING ORGANIZATIONUSAF School of Aerospace I1P~oe

Medicine USAFSAH/NGOP _________

*C. ADDRESS (City. 8&.t 004d ZIP C*d*i 7b, A009RILS (City. Sile .',d VP CJI 7Acrospace Medical Division (AFSC)Brooks Air Force Base, Texas 78235-5301

Go. NAME OF FUNOINGISPONSOMING f OFFICE SYMBOL 9. PRO0CUREMENT INSTRUMENT IDEIITIFICAVION NUMBER

Scoo of Aerospace

&C, A0049SS itly.o~ldot and ZIP COd&s 10. SOURCE Of FUNDING NOSI.

Aerospace Medical Division (AFSC) ELEMENT PR OEC N. OK UNIBrooks Air Force Base, Texas 78235-530 622 LE ME 24 NO06.NO

11. TITLE 4

HARD-COATED POLYCAR50tNATE VZRSUS V*.-39 LENSES: A FIELD STUDY* 12. PER3OIA AUTHORtSI

lTYPE ')RT 13b. TIME COVERED 14. OATA OF RE9POMT (Vr.M.. Ay) Is, PAGE COUNTFnhSt1§i r eC 198 1985 May 13

* 14, SUP1.11MENTAHY W~ TATION

17 COSATI CODES It. SUBJECT TERMS Wanfhavei on tew,,o iteets and toat~fY by Mco elniim#r

17UL GROU SUB tycarbonnte 1Lens-.; Abrasiion-Resistant Coating; Plast ic

Lenses; Ophithalmic Lznss.9I. ABSTRACT i4onlnuc on ,cuwem lfewcwi a-nd edeqtify by Nock numborj

The surface abrasion characterintics of 109 pair of spectacle lenses were evaluated _

after 1 yr of wear at Ne'Ais AFB, Nevada. One lens of each pair was an abrasion-resistant c.,vated Lexan -.401e, the other was uncoated CR-39. Data showed that the'*hard-coated Lexan lenses are more abrasion-resistant than uncoated CR-3'9.lenses.

20. OISTRIBUTIONIAVAILA81LITY OF ABSTRACT 21. ABSTRACT SECURITY CLASSIFICATION

* UNCLASSIFIED/UNLIMITELO1 SAME AS RPT. 0 OTIC USERS 0 UNCLASSIFIED* 22s. NAME OF RESPONSIBLE INDIVIDUAL 22b. TELEPHONE NI -ABER I22c. OFFICE SYMBOL

(111clu de A tea CL de)*J. W. MILLER (512) 536-3851 USAFSANk/NGOP

DD FORM 1473, 83 APR EDITION OF I AN 73 IS OBSOLETE. UNCLASSIFIEDSECURITY CLASSIFICATION OF THIS PAGE *

HARD-COATED POLYCARBONATE VERSUS CR-39 LENSES: A FIELD STUDY

IHTRODUCrION

In recent wars the percentage of wartime ocular injuries, when comparnd toall other woundo, has increased greatly. From near the turn of the centurythrough the Korean War, ocular Injuries remained constant at about 2.5X of thetotal injurLes (1). Reports from the more recent Southeast Aoia and the HiddleEast conflicts indicate the number of eye injurls ha* risen to abo ut 6 (2).

A Currently, all prescription lenses issued to militnry parsonnel are either

heat-treated glass or CR-39 plastic. While these lenses are classified by theFederal Drug Administration as "impact resistant." it is well recognized thutthey are neither unbreakable nor shatterproof. Polycarbonate (Lexan) plasticdemonstrates a tremendous capability to withstand the Inpuct of high-speedobjects (3). Even though polycarbonate plastic has very ptot abracion resis-tance, it has bcen successfully used for industrial eye r cotction and in aIrcrevhelmet visors. The soft properties of, polyarbonate preclude ntandard grindingand polishing techniques in the fabricarion of prescription polycarbonate lCns6. .

Several companies have recently developed alternate meth%A;3 for producingprescription polycarbonate lenses. All pulycarbonate lenses %ted in this studywere purchased from the Gentex Corporation. A direct comparison field-use studyof CR-39 ,rescription lensna-vs-polycarbonate prescription lerten was rompletedin 1979 (4). While the optical properties of polycarbonate were found to becomparable to other lens waterials, these lenses--even with a bati coatng--didnot posess the abrasion rtistance to bc acceptable for routine use. !eyerthe%less, from these data, polycarbouate was recommende" for issue to combatpersonnel. Shortly after the test was published, a polycarbonate ophthaltkic lensmanufacturer reported to us an improvement in hard coating state-of-the-at.Their data indicated that coated polycarbonate lenses processed with a copolymercoating gave equal or better abrasion resistance fhan the uncoated CR-39. Whileskeptical of those reports) we nevertheless conducted preliminary laboratoryabrasion tests using steel wool as an abrader. The results were quite favorablefor the coated polycarbonate lenses. In the past, poor correlation betweenlaboratory and field tests has been found for coated lens performance (5).Even so, because of these preliminary laboratory tests, the manufacturer's dataand the need for a superior eye protection material, we believed a field-use testwas in order.

PROCEDURE AND FINDINGS

Nellis Air Force Base, Nevada, was chosen as the tast ba'e. The dustyenvironment had, on previous occasions, provided a severe fipld environmenttest for lens durability performance (6). Optometry Clinic personnel supportwas obtained by request at the Nellis Hospital. Four months prior to initiatingthe test, the Nellis optometrist began a list of patients seen for roltinerefractions who would volunteer as participants. Dispersal of 152 pair ofprescription lenses mounted in metal flight frames (HGU-4/P) was made. One lensof each pair was an abrasion-resistant coated polycarbonate lenb while the otherwas uncoated CR-39. The polycarbonate lens was randomly placed in the right orleft side of the spectacle. The participants were told only that the lenseswere nonstandard, but they were to treat them as ordinary glasses.

Lens examination and sub: .1ctiLv durabilicy senrins wero made, by aregistered research opcaiann, at, 4- and 12-month intervals frum the initialdispcnsing. An 8-month evaluaw'on was planned; however, the optician'sev.luation was cancelled duu to hii illness. A durability score of 0 a noobserved scratching- I ' a few supcrficail scratches; 2 and 3 m successiveseverity oc number and penetration of P, ,!atches. Wh.le scorinS the lenses, th,optician had no record of polycarbonato lens placement (ritht side, left side).The optician'e 4-month lens score records were purposely not availabl, duringthe 12-month on-site evaluation. Additionally, the participants were asked ccomplete an evaluation form, shown in Figure I.

I. DIA you Veoir the l10es allthe tiltl YES NO I NO, d1d you

wear the Si8e64.: SOT Of 11[ TIlME _AU.DLY AT ALL

2, Wert the glases comforcble? YES _ M _ _ If We IMIcatt tht

ycobUA . ... .... .

3. Is lther of y leses scrayttrh-d or atrre? - -10 i it.

which one? RIGHT_ LZFT 0- O - It bathe which is vorset

RTCjT LiT - Did Any unumsal event costribute to the Ions dam-

age? YES NO If YES, . leaae calplali _,

A 4. To what excent dots the scratch or rar lnterfere with your vision?

- A CErAT DCAL S _ NOT AT ALL

5. Were there uny unusual exptrlnced noticed with spectacle wear?

YES - NO If YES, pleas, explain

6. Now do you usually clean your lenses?

hMANDIKERCHIET WET DRY

KLEEKX __ T DRY

PAPER TO EL WET DRY _-

OV ER (Pleaae Explain) .WET DRY

7. Do you think thet the lenses used In the test should be considered for

standard military spectcles? 'hIUT LENS: YES NO

LEFT LNS: YES NO

COMOENTS:________________________ ____

Figure 1. Questionnaire for u'ers' evaluation of lenses.

2

The participants were told that lenses would be replaced should lens dctce-

'; frioration become unacceptable for wear. If this occurred, treated glass lenses

were to be used and the participant would be discontintued from the study.

One week prior to lens-evaluation dates, postcards were mailed to theparticipants requesting them to bring their Classes to the Nelli, OptometryClinic. A notice of evaluation dates was plced in the Ne1lis Base ,silletin.The response rates were: 4 months, 77% (117/152), and 12 non.hs, 89Z (97/109).During the study a total of 43 participants asked for new lenses. Data fromtheir test spectacle lenses are included in the analysis. No effort was madeto assess the cause of additional subject loss. Previous field studiesindlcated loss due primarily to military transfer.

Table 1 presents the sumary of the optician's abrasion scores for eachspectacle pair of lenses At the 12-month evaluution. For example, 10 pair ofspectacles shoved a CR-39 durability score of 1, and a polyearbonate score of0. The optician recorded the same score for both lenses on 50 pair of specta-cles (Diagonal Data: 14 + 8 + 14 + 14). On 32 of the remaining 47 pair, thescore was worse for thd CR-39 than the polycarbonate (p <.05). These datawere generally In agreement vith the 4-month data (Table 2)1 where the polycar-bonace lenses were also reported as less abraded thin the CR-39 (p <.01).

TABL 1. OPTICIAN'S SCORE FOR EACH CR-39 AND-,. POLYCARBONATE LMS PAIR ON 97 SUBJECTS

(-monch evaluation)

CR-39 lens score

0 1 2 3

0 14 10 4 2

*1 4 8 7 5:.-

2 4 6 14 49.p.%

3 1 0 0 14

NOTES:

.... 1. CR-39 mean score: 1.542. Polycarbonate mean score: 1.29

3

TABLE 2. OlTCIAN'S SCOIRE FOR FACH CR-39 MND.'OL¥YCARBONAT7 LENS PAlt ON 115 SUIJECTS*

(4-month evaluation)

C.

0 27 15 6 0(C

4 j1 9 23 7 5..

2 0 8

O -4 "m

Data incomplete on 2 subject$

. CR-39 mean score: 3.07-

I. Polycarbonate mean score: .83':3. Based on the asstumption that the Jifference between the scores representsequal increments of severity of scratchingl.

It

In order to measure the accuracy of the opti;ctan'xs coring one would need ,'independent repeated ecorings on the some Ions under identical conditions. Since .,

these data were not available, i.t wes decided tv check on the consistency of theoptician's scoring by comparing abrasioua scores between the 12-month and the,4-month evaluations. One would expect the lans to get worse over tite (greater 'scores) or at bent stay the same. Any "improvement" over tine (omall1 scores) can .be thought of as an error n scoring. The conparson of the abrasion scores

between the 4- and 12-sonth evaluations for polycarbonate and CR-39 separately.:is gien in Table 3. : dentical scores were reSoded for 33 polycarbonste lenses(Diagonal Data). Only 6 polycarbonate lens scores (4 + I + 1) out of 78 lensesshowed "Improvement" (lers scratching at 12 onths than at 4 months). Of the

C-39 len scores, 30 lenses were scored dentical whl 10 (6 + + 3) o 79dihowed "etprovemen" by 1 score only. These esuls indnicated that the optician'sscoring criteria were consistent, Remeber thad dn Table 3 no comparison was hemode tween CR-39 and polycarbonste lenses, only between 12- and 4-month data of

the aete lenses. Os4

TABLE 3. CONSISTENCY CIMK ON 0PTICIAN'S SCORES

...-.... 4-montli vs 12-montlh evaluation)

Polycarbonate CR-39

4-monch scores 4-month scores

03 2 3

m 0 is 4 1 1 0 11 6 0 0

0U 1 10 10 0 0 1 9 10 1 3

, 2 4 12 4 0 2 3 7 6 3

:3 2 4 7 1 3 3 7 10 1.-

Total: 78* Total: 79

* Data missing for one subject

The lenses with the worst abrasion, &s reported on question 3 of theparticipants' subjective questionnaire (Fig. 1), were compared to thepolycarbonate lenses, as shown in Table 4. Only 18 of 60 times was polycnrbonatechosen by subjects to be the worst lens (p <.01). This finding was consistentwith the results of the other 2 evaluations.

5

sI

-." m- 8i ; - i i n n m n i m r m i - - . . . . ' " - . . . . . -" " " " '' "

TABLE 4. QUESTION 3: LENS WITH WORSE SCIU\TCHINGCOMPARED TO POLYCARBONATE LENS ON 60 SUBJ1ECTS

(12-montl evaluation) -

Worst lens

.0ii. . Right Left.

Right 5 21

0 Left 21 13

Explanation for incomplete data:

29 reported no 3cratching

5 reported both lenses scratched, but never reported which lens was worne

I reported scratching, but did not Bive any location

2 missing data

37 + 60 above - total of 97 evaluated at 12 oonths

The responses to question 7 were analyzed in the same manner as theoptician's scores. The results are displayed in Table 5, The diagonal data(59 and 4) do not aid in deciding the preference for CR-39 or polycarbonate.The off-diagonal data (15 vs 3) suggest that generally the polycarbonatelenses are preferred to CR-39 (p <.01). These data are in good agreementwith the reoults for the 2 previous evaluations.

6

TABLE 5. RESPONSE TO QUESTION 7 FOR EACH CR-39 ANDPOLYCARIOATE PAIR ON 81 SUIJECTS

(12-month evaluation) _-------,-

NOTE: NoCR-39 len T

".:Yes No Total

" No 3 4 7

0 Total 62 19 81~(76.5%)

NOTE:

Eleven subjects did not respond to questLon 7; 5 subjects responded only topart of the questions.

11 + 5 + above 81 - total of 97 eval]uatd at 12 months

Summary of responses to questions 1 and 2 at the 12-month evaluation isgiven in Table 6. Genernly, the results showi that at least 90% of the par-ticipants wore these spectacles most of the time and that they were comfortable.The responses to questions 4, 5 and 6 were not reported since the data were notavailable by lens type.

7I

TABLE 6. SUwxARY OF R SPO1SES TO qUESTIONS I AND 2

---., ( 12-month evalu.ation) -.....

No. question Response.D you wear the glset ni tile time?i-

YeS 58/95 (61.12)

Host of the time 30/95 (3l.6Z)

Hardly at all 7/95 (7.4g,)

2 Were the &asses comfortable? 90/95 (94.7%)

* The percentages are based on the total number of subjects who responded to

the question, not the total number of subjecto evaluated (97).

CONCLUSIONS

The data from this field-use study showed that hacd-coated polycarbonatelenses were more abrasion-resistant than uncoated CR-39 lenses after about1 year of field use. Data were consistent from both the optician's and partic-ipants' responses on both the 4- and 12-montb evaluations.

RECOHMENDATIONS

A coated polycarbonate prescription lens with acceptable field life is nowavailable to provide superior eye protection. To recomend this lens as asubstitute for glass or CR-39 materials is premature. Field tests using liveweapons for real-world ballistic performance are needed. hterial thicknesseffects should be investigated. The cost of lens fabrication, includinglaboratory tooling costs, must also be consiecred.

We do recommend that bard-coated polycarbonate lenses be issued to combatpersonnel potentially exposed to antipersonnel weapons. Rescue crows, low-levelflight crews, armored infantry, and tank crews would certainly benefit from thisprotection.

8

RUFRE CES

I. Tredici, Thomas J. Managenent of ophthalmic casualties in Southeast Asia.ilit Med 133(5):355-362 (1968).

2. Belkin Michael. Ocular trauma during Yom Kippur War, Combat ocularproblems, pp. 15-20. In Conference Proceedings, Lottceran ArmyInstitute of Research, Presidio of San Fernando, California,Oct 20-21i 1980.

3. Report No. 8-26, Lexan sheet. General Electric Pittsfield,Massachusetts, undated.

4. Miller, J. W., Kislin, ttnj*ait Tredici, Thoiss J., and Rahe, Alton J.Polycarbonate versus CR-39 lenses: A field study. SAM-TR-79-42,Dec 1979.

5. Provines, Wayne F., Targove, Bertram D., and Kislin, Nenjamin. Ghosutimagery intensity and durability of selected anti-reflectant coati,14.Am J Opton Arch A m Acad Optox 50(1):34-39 (1973).

6. Targove, Bertram D., Miller, J. W., Tredici, Thomas 3., Kislin, Benjamin,Rahe, A. J., and Provines, Wayne F. Glass versus plastic lenses--AnAir Force replacement and durAhility study. Am . Optom 49(4):320-329(1975).

_. !i--