Investigative Ophthalmlgy & Visual Science, Vl. 3, N. 9, September 99 Cpyright Assciatin fr Research in Visin and Ophthalmlgy Acuity Card Assessment f Visual Functin in the Crytherapy fr Retinpathy f Prematurity Trial Velma Dbsn,* Graham E. Quinn,f Albert W. Biglan,^: Berry Tung, Jhn T. FlynnJ and Earl A. PalmerU The primary utcme measure f the effectiveness f crytherapy in the riginal design f the Multicenter Trial f Crytherapy fr Retinpathy f Prematurity (CRYO-ROP) was the anatmic status f the retina, as dcumented by fundus phtgraphy 3 mnths and 2 mnths after infants had received treatment. The authrs describe the additin f a measurement f visual functin, the Acuity Card prcedure, t the CRYO-ROP study. After training, fur visual-acuity testers attempted t measure mncular grating acuity in all randmized infants and apprximately ne furth f the natural-histry infants in the study, tested at year pstcrytherapy r year pstterm. In 9% f infants n whm testing was attempted, mncular acuity values frm each eye were btained. Interbserver test-retest results n 2 eyes f 3 randmized infants agreed t within ne ctave r better in all but ne f the eyes. The high testability rate and gd interbserver agreement suggest that the Acuity Card prcedure has been a successful methd f assessing visual functin in the CRYO-ROP study. Invest Ophthalml Vis Sci 3:72-78, 99 In the riginal design f the Multicenter Trial f Crytherapy fr Retinpathy f Prematurity (CRYO-ROP), the primary measure f the effectiveness f crytherapy was the anatmic status f the retina, as dcumented by fundus phtgraphy, 3 mnths and year after treatment. A quantitative measure f visual functin was nt included because the quantitative measures available were labratrybased techniques that were still in the develpmental stage, were time cnsuming, and required technical expertise that precluded their incrpratin int this multicenter trial. Subsequent t the initiatin f the CRYO-ROP study, the Acuity Card prcedure 2 emerged as a rapid, easy-t-administer, behaviral methd fr assessment f grating (spatial reslutin) Frm the Departments f *Psychiatry and Psychlgy, and ^Ophthalmlgy, University f Pittsburgh Schl f Medicine, Pittsburgh, Pennsylvania; fdivisin f Pediatric Ophthalmlgy, Children's Hspital f Philadelphia, University f Pennsylvania, Philadelphia, Pennsylvania; Schl f Public Health, University f Texas Health Science Center at Hustn, Hustn, Texas; Department f Ophthalmlgy, University f Miami, Miami, Flrida; and UDepartment f Ophthalmlgy, Oregn Health Sciences University. On behalf f the Crytherapy fr Retinpathy f Prematurity Cperative Grup. A full listing f the Crytherapy fr Retinpathy f Prematurity Cperative Grup can be fund in the first reprt f the results f the Crytherapy fr Retinpathy f Prematurity study. Supprted by a cperative agreement ( U EY874) frm the Natinal Eye Institute. Reprint requests: Velma Dbsn, PhD, Department f Psychlgy, Langley Hall, University f Pittsburgh, Pittsburgh, PA 26. visual acuity in infants and nnverbal children. Because f the need t evaluate the effect f crytherapy n visin, the Executive Cmmittee f the CRYO- ROP study incrprated the measurement f mncular grating acuity at the -year fllw-up examinatin as a measure f functinal visual utcme after crytherapy. We describe the incrpratin f Acuity Card testing int the CRYO-ROP trial and evaluate the effectiveness and reliability f the Acuity Card Prcedure as a measure f visual acuity in that trial. Materials and Methds Patients were enrlled int the CRYO-ROP trial frm January 986 t Nvember 3, 987. All infants were < 2 g at birth, and they participated in either the "natural histry" r "randmized" segments f the clinical trial. Details f enrllment, randmizatin, and fllw-up are available elsewhere. As part f the -year examinatin, questins designed t assess develpmental status were asked cncerning the infant's ability t sit, t grasp an bject and resist having it remved frm his r her hand, and t shw a clear respnse t sund. Develpmental status was judged t be satisfactry if the infant culd perfrm tw f these three tasks. Incrpratin f Acuity Card testing int the CRYO-ROP trial invlved three phases: () the develpment f a prtcl, (2) training f testers, and (3) the testing f infants in the study. 72 Dwnladed Frm: http://ivs.arvjurnals.rg/pdfaccess.ashx?url=/data/jurnals/ivs/9338/ n /2/27
N. 9 ACUITY CARD TESTING IN THE CRYO-ROP TRIAL / Dbsn er l 73 Prtcl Develpment The initial phase created a prtcl that wuld prvide mncular acuity estimates in bth the treated and untreated eyes f all infants wh had been randmized t crytherapy. Fur aspects f measurement f visual acuity were cnsidered: () the best methd t use, (2) when t measure visual acuity, (3) hw t measure visual acuity in the widely scattered study ppulatin, and (4) incrpratin f measures t ensure quality cntrl. The Acuity Card prcedure was chsen as the methd fr measuring visual acuity because f the speed and ease with which it can be administered and because previus research had shwn that it culd be used effectively in infants. 3 The decisin cncerning when t test was straightfrward: fllw-up eye evaluatins f all infants in the CRYO-ROP study were being scheduled 3 and 2 mnths after treatment, s that acuity testing culd be added at either age with minimal incnvenience t the parents r study-center crdinatrs. Because visual acuity in nrmal, full-term infants is better at 2 than at 3 mnths f age and because mst study infants had already cmpleted the 3-mnth examinatin, it was decided t add acuity testing t the 2- mnth fllw-up examinatin. The issue f hw t test all treated (randmized) infants was cmplicated because the infants were lcated at 23 centers distributed acrss the United States. The mst efficient methd wuld have been t certify a persn as an acuity tester at each center. Hwever, because the Acuity Card prcedure was a newly develped technique, it was nt clear that adequate quality cntrl f the data culd be maintained with a part-time tester at each center. In additin, the Acuity Card prcedure requires frequent practice fr a tester t maintain skills at the level required t assess visually r neurlgically cmprmised infants reliably. Therefre, fur full-time testers were selected, each f whm was based at ne f the CRYO- ROP centers and assigned t assess all study infants (bth randmized and nnrandmized) at their base (hme) center and the randmized infants at five t six remte centers. In additin t limiting the number f acuity testers t fur, the fllwing quality-cntrl measures were incrprated int the prtcl:. Testers were masked t the medical/cular histry f the infants, particularly t which eye f each infant had been randmized t crytherapy. 2. Every 6 mnths, the testers were reassigned t different centers fr testing randmized infants. This minimized the pssibility f the testers' learning which eye f an infant had been treated. It als distributed acrss all study centers any individual differences amng testers. 3. Testers participated in a -day quality-cntrl sessin every 6 mnths. During this sessin, the testers watched each ther cnduct Acuity Card assessment f several infants and discussed testing-related issues with the experimental psychlgist (V.D.) and pediatric phthalmlgist (G.Q.) directing the acuity-assessment prtcl. 4. Between June 988 and June 989, each available, cperative randmized infant at the testers' hme centers was tested twice: first by a tester frm anther center and then by the hme tester. This part f the prtcl prvided data n interbserver testretest reliability.. In additin t assessing randmized infants at five t six remte centers, each tester als measured the acuity f all natural-histry (nt randmized) infants at her wn center. This assured that testers evaluated infants withut significant visual disrders, maintained skill in the technique, and prvided visual acuity data n a subset f the natural-histry ppulatin. Training f Testers Fur visual-acuity testers were trained. Each tester studied the Teller Acuity Card Handbk, 4 the manual f prcedures fr visual-acuity testing in the CRYO-ROP study, and a review f the Acuity Card prcedure by Teller et al. 3 The testers then attended a -day training sessin: they first watched tw experienced testers cnduct the Acuity Card prcedure, then the experienced testers watched the fur CRYO-ROP testers cnduct the prcedure with five t seven infants. T gain mre experience, each tester then tested -8 nnstudy infants with and withut cular abnrmalities at their hme center. Testers were certified when they cmpleted mncular acuity assessment f bth eyes f at least eight infants wh had n cular abnrmalities and whse scres fell within the nrmal range. All testers were certified within 6 weeks f the initial training sessin. As a final check n the testers' prficiency, ne f the trainers bserved the testers' technique during a -day sessin held 2 mnths after the initial training sessin. Testing f Infants Each tester carried a set f 7 Acuity Cards, including the "Lw Visin" card, with her t the centers. Each f the 23 study centers was prvided with an Acuity Card screen (Vistech). Figure illustrates the use f the cards and screen during testing. Dwnladed Frm: http://ivs.arvjurnals.rg/pdfaccess.ashx?url=/data/jurnals/ivs/9338/ n /2/27
74 INVESTIGATIVE OPHTHALMOLOGY & VIUAL SCIENCE / September 99 * fr Fig.. Measurement f grating acuity with the Teller Acuity Card Prcedure. Infant is seated n parent's lap with eyes 38 cm frm the center f the Acuity Card. The tester (behind the screen) presents a series f Acuity Cards {the.32 cycle/cm card is shwn here) and watches the infant's eye and head mvements thrugh a peephle in the center f the card. Based n the infant's preferential fixatin f the gratings n the Acuity Cards presented, the tester estimates acuity as the finest grating that the infant gave evidence f being able t reslve. Testing was cnducted either befre the phthalmlgist's examinatin at the i-year fllw-up visit r at anther visit, separated frm the rest f the eye examinatin. Infrmed cnsent was btained frm each infant's parent r guardian after the prcedure was explained and befre testing. During testing, the parent held the infant 38 cm in frnt f the pening in the screen where the Acuity Cards were presented. The cards were stacked face dwn behind the screen, frm the lwest t the highest spatial frequency (frm larger t smaller stripe widths). Placing the cards face dwn allwed the tester t present each card withut knwledge f whether the grating was lcated t the left r t the right f the peephle n each individual card. Initially, the tester presented the card cntaining the.3 cycles/cm* grating and decided, n the basis f the infant's eye and head mvements, whether the child culd reslve the grating.f If the tester judged that the child culd reslve the grating, cards cntaining finer and finer gratings were pre* A cycle cnsists f ne black and ne white stripe. The width f each stripe in the.3-cycles/cm grating is.4 cm, the width f each stripe in the.32-cycle/cm grating is.6 cm, and the width f each stripe in the "Lw Visin" card is 2.2 cm. At a test distance f 38 cm, the.3-cycles/cm grating prduces a visual target f.9 cycle/ degree. Mre detail abut the manner in which the tester uses the infant's behavir t judge whether r nt the infant can reslve the grating is reprted in Teller et al.3 Vl. sented, until the infant shwed n evidence f reslving the gratings. If the child's eye and/r head mvements prvided n evidence that he r she culd reslve the.3 cycles/cm grating, the tester presented the card cntaining the.32 cycle/cm* grating (very large stripes). If the child's eye and head mvement respnse t that card indicated t the tester that he r she child culd reslve that grating, then cards cntaining finer and finer gratings were presented until the tester judged that the child shwed n evidence that he r she culd reslve the grating. If the child prvided n evidence that they culd reslve the.32 cycle/cm grating, the tester used the "Lw Visin" (.23 cycle/cm*) card as a final attempt t dcument pattern visin. The acuity threshld was estimated by the finest grating that the tester judged that the child culd reslve. During the examinatin, the testers were required t present each card at least twice, nce with the grating n either side f the peephle, and they were permitted t present each card as many times as necessary t reach a decisin cncerning whether r nt the infant culd reslve the grating n the card. Testers were required t remain masked t the lcatin f the grating n each card until they had reached a decisin as t whether the infant reslved the grating. After they reached a decisin abut the visibility f the grating t the infant, testers were allwed t examine the frnt f the card t cnfirm their judgment abut the lcatin f the grating n the card. The test distance was changed under tw circumstances. First, if the infant began t play with the shield that blcked the parent's view f the screen, the infant was mved back t a measured distance f cm. Secnd, if the infant was unrespnsive t the lwest spatial frequency grating at 38 cm, the tester came ut frm behind the screen and presented the cards directly in frnt f the infant at 38 cm r, if necessary, at 9 cm r cm. Other mdificatins in prtcl included vertical presentatin f the cards fr children with nystagmus, and presentatin f the cards at varius field lcatins in lw-visin patients, in an attempt t find an area f frm visin. Scring f results: The tester recrded the test distance, the spatial frequency (cycles/cm) f the finest grating that the tester judged that the infant culd reslve, and a cnfidence rating. Nnstandard prcedures (eg, testing withut the screen and testing with the cards held vertically) and general cmments were als recrded. If a tester was unable t btain an acuity estimate frm ne r bth eyes, the reasn fr the incmplete test (eg, fussiness r sleepiness) was recrded. Dwnladed Frm: http://ivs.arvjurnals.rg/pdfaccess.ashx?url=/data/jurnals/ivs/9338/ n /2/27
N. 9 ACUITY CARD TESTING IN THE CRYO-ROP TRIAL / Dbsn er l 7 The testers did nt discuss acuity results with the parents. A graph shwing the child's results relative t age nrms was given t the examining phthalmlgist after he r she cmpleted the phthalmlgic examinatin. Acuity results were prvided t the parent by the phthalmlgist, in the cntext f the cmplete eye examinatin. One cpy f each infant's data sheet was sent t the CRYO-ROP Crdinating Center, ne cpy was given t the Study Center Crdinatr fr placement in the child's medical recrd, and ne cpy was retained by the tester. Acuity scres were cnverted t cycles/degree by the Crdinating Center, based n the raw scre in cycles/cm and the distance at which the test was cnducted. Retests: Retests were required if ne r mre f the fllwing ccurred:. The tester was unable t btain an acuity estimate frm each eye f the infant. 2. The eye examinatin cnducted at the 2- mnth fllw-up revealed a substantial refractive errr, denned as uncrrected mypia greater than -4.7 dipters (D), uncrrected hyperpia greater than +6. D, uncrrected astigmatism greater than 3. D in ne r bth eyes, r anismetrpia greater than 2. D spherical equivalent r cylinder if amblypia was suspected by the examining phthalmlgist. In this case, retest with crrectin was required, after the infant had wrn the prescribed crrectin fr at least mnth. 3. The eye examinatin cnducted at the 2- mnth fllw-up revealed the presence f amblypia, in the absence f retrlental membrane, retinal detachment invlving the macula, r a macular fld. Amblypia was diagnsed by an cular preference in the fixatin behavir. If amblypia was judged t be present, a retest was required after mnth f amblypia therapy, as prescribed and mnitred by the treating physician. Testability Rates Results Table presents the testability rates fr Acuity Card testing f the 9 infants in the randmized grup and the 624 infants in the natural-histry grup wh were tested between Octber 987, when the first tester was certified, and June 989. Within each grup, the develpmental status f infants was brken dwn int three categries: satisfactry, abnrmal, and unknwn. A successful Acuity Card test was defined as any f the fllwing: measurable grating acuity, reslutin f nly the.2 cycle/cm grating n the "Lw Visin" card, light perceptin nly, r n light perceptin. Success rates fr cmpleting tw mncular tests were similar in the randmized and natural-histry grups, irrespective f develpmental status. Fr the grup f infants n whm a mncular acuity test was cmpleted fr each eye, Table 2 shws the number f tests each infant cmpleted. In mst infants, in bth the randmized and the natural-histry grups, it was necessary fr the tester t cnduct nly tw acuity tests (ne per eye). Fr 33 infants Table. Success rates fr acuity card testing (2 mnths) Tests cmpleted Grup and develpmental status Number tested Tw mncular Only ne mncular Only bincular N tests cmpleted Randmized Satisfactry Abnrmal Unknwn Ttal randmized Natural Histry Satisfactry Abnrmal Unknwn Ttal natural histry 74 9 6 9 624 64 (94.2%) (.%) (.%) 8 (94.8%) 74 (9.7%) 8 (94.7%) 4 (8.%) 96 (9.%) (2.9%) (2.6%) 4 (2.3%) (2.%) (2.4%) (2.9%) (2.6%) 2 (2.%) (.3%) 3 (2.%) Dwnladed Frm: http://ivs.arvjurnals.rg/pdfaccess.ashx?url=/data/jurnals/ivs/9338/ n /2/27
76 INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE / September 99 Vl. 3 Table 2. Number f tests required t btain tw mncular acuity estimates (2 mnths) Grup Randmized Natural histry Number tested 2 Tests 3-4 Tests >4 Tests 8 96 47 (8.7%) 68 (9.3%) 2 (3.9%) 24 (4.%) (4.4%) 4 (.7%) (8%) in the randmized grup and 28 infants (%) in the natural-histry grup, hwever, mre than ne test per eye was needed because the eye was tested initially withut adequate ptical crrectin, because the eye was tested befre amblypia therapy, r because the infant did nt cperate during the initial test. Interbserver Agreement Figure 2 shws interbserver test-retest agreement fr the 3 randmized infants n whm ne r bth eyes were tested by tw testers. (Interbserver testretest cmparisns were nt cnducted n infants in the natural-histry grup.) With ne exceptin, all data pints in which a measurable grating acuity was btained fall within the slid lines indicating interbserver agreement f ne ctave$ (tw cards) r better. The ne exceptin is a case in which the pri- $ An ctave is a halving r dubling f spatial frequency; eg, frm 38 t 9 cycles/cm r frm t 3 cycles/degree. mary tester said the acuity was 3.3 cycles/degree, and the hme tester said that the child had n spatial visin. Fr the 4 test pairs n which measurable grating acuity values were btained by bth testers, the mean interbserver difference was.44 ctave (standard deviatin =.3 ctave). The minimum interbserver difference was ctave, and the maximum was. ctave. Discussin Our results indicate that the Acuity Card prcedure was incrprated successfully int the Multicenter CRYO-ROP Trial. Thus far, acuity assessment has been undertaken at 2 mnths pstcrytherapy in 9 infants wh were randmized t crytherapy, and at 2 mnths crrected age in 624 infants in the natural-histry segment f the study. In 9% f infants in the randmized and in the natural-histry grups, an estimate f mncular acuity was btained frm bth eyes f the infant. In all remaining infants, either a mncular acuity estimate was btained frm ne eye r a bincular acuity estimate was btained. The success rate fr btaining mncular acuity results in infants wh failed tw f three mtr/neurlgic screening tests was as gd as the success rate in the rest f the study ppulatin. Interbserver agreement was examined in 2 eyes f 3 randmized infants, and in nly ne case (4%) did the bservers differ by mre than ne ctave in their estimates f acuity. The finding that the Acuity Card prcedure pr- CD LLJ 2 C\] C LJ I LU I Q < 6 3 LP NLP m <mm cm jr cm / / ^a» NLP LP 3 6 2 ACUITY BY TESTER # (CYCLES/DEG) - Fig. 2. Test-retest agreement fr 3 right eyes (O) and 2 left eyes ( ) f 3 infants in the randmized grup wh were tested by tw visual acuity testers. The secnd test was perfrmed n the same day as the first test by a tester wh was unaware f the results btained by thefirsttester. Slid diagnal lines indicate interbserver agreement f ± ctave. Ten eyes shwed n measurable grating acuity, as indicated by acuity scres f n light perceptin (NLP) r light perceptin nly (LP). Dwnladed Frm: http://ivs.arvjurnals.rg/pdfaccess.ashx?url=/data/jurnals/ivs/9338/ n /2/27
N. 9 ACUITY CARD TESTING IN THE CRYO-ROP TRIAL / Dbsn er l 77 duced an estimate f acuity in % f infants in whm testing was attempted indicates the strength f this prcedure as a tl fr acuity assessment, even in a ppulatin with a high prevalence f medical, neurlgic, and visual cmprmise. The rbustness f the prcedure is further supprted by thefinding that, in 9% f bth the randmized and natural-histry infants, the study gal f btaining tw mncular acuity estimates per infant was met. The mncular testability rate f 9.% is cnsiderably better than the value f 8% reprted fr all 9- t 2-mnth-ld patients and all preterm patients with cular disrders in the nly ther large-scale study in which Acuity Cards were used t assess mncular acuity in clinical settings. In fact, it is identical t the mncular testability rate fund by McDnald et al 6 fr a small grup f nrmal, full-term infants. One difference between the current study and previus studies is that testers in ur study were required t retest infants wh did nt cmplete tw mncular acuity tests, whereas success rates in previus studies were reprted n the basis f ne test per eye per infant. Examinatin f the data f individual infants indicates, hwever, that in all but three infants (all in the randmized grup), the retests were cnducted because the infant needed glasses r amblypia therapy, nt because the child did nt cperate during testing. Thus, the high success rates in ur study are nt due t the fact that retests f uncperative infants were cnducted. Instead, the high success rates prbably reflect the dedicatin and persistence f the fur visual-acuity testers. The number f infants n whm test-retest infrmatin was available is small. This is because initially (frm Octber 987 thrugh May 988) each tester examined randmized infants at her hme center, and therefre, at n time were tw testers available t evaluate the same infant. After May 988, the primary tester fr randmized infants at a tester's hme center was a tester frm anther center. Therefre, fr these infants, it was usually pssible t have the hme tester available t cnduct a secnd test after the primary tester had cmpleted the prcedure. The 3 infants n whm test-retest results are presented in Figure 2 represent all randmized infants at the testers' hme centers wh were scheduled when a. secnd tester was available and wh remained cperative enugh t cmplete testing with a secnd tester. Despite the relatively small number f infants wh participated in the test-retest cmparisns, the finding that 93% f interbseryer test-retest cmparisns f randmized infants agreed t ne ctave r better cmpares with the results f previus studies that examined interbserver agreement in mncular Acuity Card r frced-chice preferential lking (FPL) testing f -year-ld infants. McDnald et al, 6 in an Acuity Card study f nrmal, full-term - t 2-mnth-ld infants, fund that 86% f interbserver cmparisns agreed t ne ctave r better. Dbsn et al 7 fund interbserver agreement f ne ctave r better in 8% f cmparisns f mncular Acuity Card scres in 47 ne-year-lds wh had been treated in a nenatal intensive care unit. The FPL studies by Maurer et al 8 shwed interbserver agreement f ne ctave r better in 93% f mncular tests f 7 nrmal 6- t 2-mnth-lds but nly in 79% f mncular tests f 6- t 36-mnth-ld aphakic children. Finally, cmparisn f the mean interbserver difference f.4 ctave fund in the current study with that reprted in previus studies indicates that ur finding is similar t the value f.3 ctave fund by Birch and Hale 9 fr nrmal 9- t - mnth-ld infants tested mncularly with the FPL prcedure and better than the value f.6 fund by Dbsn et al 7 fr Acuity Card testing f -year-ld infants wh had been treated in a nenatal intensive care unit. The agreement between the test-retest results f the current study and thse f previus studies supprts the validity f the Acuity Card prcedure as a measure f grating acuity in the difficult-t-test ppulatin f randmized infants in the CRYO-ROP study. In cnclusin, the additin f a measure f visual functin as a supplement t the CRYO-ROP study was nt a straightfrward matter. The study, already underway, had clearly defined endpints at 3 and 2 mnths pstcrytherapy (r pstterm) based n structural changes in the retina. As intake prceeded but results were still unknwn, the Executive Cmmittee decided that an early evaluatin f functinal utcme was feasible and was extremely imprtant. Althugh the Acuity Card prcedure was new and relatively untested, it was chsen as the measure f functinal visin fr the study because it was fast and technically simple enugh t be used in a large-scale assessment f nnverbal infants. Our data indicate that incrpratin f this prcedure was nt nly successful, but it resulted in mncular acuity results frm ver 9% f infants tested. Test-retest reliability was as high as that fund previusly in infants with less severe visual deficits than thse f many f the randmized infants in this study. We hpe that ur success with this methd in this challenging ppulatin will be encuraging t thers wh need t assess visual acuity in yung r nnverbal children. Key wrds: grating acuity, acuity cards, retinpathy f prematurity, infants, interbserver reliability Dwnladed Frm: http://ivs.arvjurnals.rg/pdfaccess.ashx?url=/data/jurnals/ivs/9338/ n /2/27
78 INVESTIGATIVE OPHTHALMOLOGY 6 VISUAL SCIENCE / September 99 Vl. 3 Acknwledgments The results f this study are a tribute t the hard wrk, dedicatin and ingenuity f the fur visual-acuity testers: Janice Evans, MEd, Annette Hammel, BFA, Laura Trueb, MA, and Patricia Whitehill, BS. They are als a tribute t the patience and cperatin f the members f the CRYO-ROP Cperative Grup, in particular the Study Center Crdinatrs, in adding a new prcedure int the nging clinical trial. The authrs thank E. Eugenie Hartmann, PhD, Gerge Ellis, Jr, MD, Angela Lve, BS, Herbert Kaufman, MD, and the Luisiana State University Eye Center fr assistance in training the testers. They als thank the persnnel and staff f the Natinal Eye Institute wh were sensitive t the critical time cnstraints necessary fr implementatin f the prject, in particular Jhn Finerty, PhD. References. Crytherapy fr Retinpathy f Prematurity Cperative Grup: Multicenter trial f crytherapy fr retinpathy f prematurity. Arch Ophthalml 6:47, 988. 2. McDnald MA, Dbsn V, Sebris SL, Baitch L, Varner D, and Teller DY: The Acuity Card prcedure: A rapid test f infant acuity. Invest Ophthalml Vis Sci 26:8, 98. 3. Teller DY, McDnald MA, Prestn K., Sebris SL, and Dbsn V: Assessment f visual acuity in infants and children: The Acuity Card prcedure. Dev Med Child Neurl 28:779, 986. 4. Teller Acuity Card Handbk. Daytn, Ohi, Vistech Cnsultants, 986.. Sebris SL, Dbsn V, McDnald MA, and Teller DY: Acuity cards fr visual acuity assessment f infants and children in clinical settings. Clin Visin Sci 2:4, 987. 6. McDnald MA, Sebris SL, Mhn G, Teller DY, and Dbsn V: Mncular acuity in nrmal infants: The Acuity Card prcedure. Am J Optm Physil Optics 63:27, 986. 7. Dbsn V, Carpenter NA, Bnvalt K, and Bssier J: The Acuity Card prcedure: Interbserver agreement in infants with perinatal cmplicatins. Clin Visin Sci (in press). 8. Maurer D, Lewis TL, and Brent HP: The effects f deprivatin n human visual develpment: Studies f children treated fr cataracts. In Applied Develpmental Psychlgy, Mrrisn FJ, Lrd CE, and Keating DP, editrs. San Dieg, Academic Press, 39-227, 989. 9. Birch EE and Hale LA: Criteria fr mncular acuity deficit in infancy and early childhd. Invest Ophthalml Vis Sci 29:636, 988. Dwnladed Frm: http://ivs.arvjurnals.rg/pdfaccess.ashx?url=/data/jurnals/ivs/9338/ n /2/27