BritishJournal of Ophthalmology 1996;80:617-623

Transillumination of iris and subnormal visualacuity-ocular albinism?

Lena Sj6dell, Anders Sj6str6m, Maths Abrahamsson

AbstractBackground-A common clinical sign inchildren with subnormal visual acuity orslow visual development was iris transillu-mination. This was used as the inclusioncriterion in a study of children shown tohave a subnormal visual acuity in ageneral health examination at age 4 years.Methods-Refraction values, stereopsis,fundus photography, macular and nervehead appearance, and visual evoked re-sponse (VER) recordings were studied in18 children.The clinical results were com-pared with 64 controls referred to the eyeclinic because of subnormal vision fromthe general health examination or fromschool health care.Results-Eight children had VERs show-ing asymmetry typical for albinism. An-other four had only small asymmetries onthe VER, indicating a lower degree ofdecussation abnormality. No simple cor-relation of visual acuity, degree of iristransillumination, stereopsis, or macularpathology and VER asymmetries werefound. However, marked iris transillumi-nation in all four quadrants, absence of afoveal reflex, and low visual acuity wereweakly correlated.Conclusions-In a rather homogeneousgroup of children with iris transillumina-tion and subnormal visual acuity eight of18 had typical albinoVERs.The findings ofsmall atypical VER asymmetries in fourchildren and no asymmetry in six childrensuggest that albinism may be consideredas a description of a heterogeneous groupof conditions including maximal decussa-tion rate (100%) in the chiasma to a condi-tion with almost normal (¢50%)decussation rate.(BrJ Ophthalmol 1996;80:617-623)

Albinism is usually characterised by nystag-mus, foveal hypoplasia, photophobia, iris trans-lucency, neuronal abnormalities, and de-creased visual acuity,'" but manifestations mayvary considerably and albinism may be diag-nosed only as a result of a subnormal visualacuity, or by chance.7 8Albinism is a geneticallydetermined disorder of the melanin pigmen-tary system5 '0 which gives a hypopigmentationof skin, hair, and eyes (oculocutaneous albi-nism, OCA) or a hypopigmentation of the eyesonly (ocular albinism, OA). The melanocytesof the pigment epithelial layers of the retina,ciliary body, and iris are derived from the outer

layer of the optic vesicle (neuroectoderm).This melanogenesis occurs early, already bythe fifth week of fetal life, and it is thought to becompleted at or soon after birth." By the ninthgestational week there is a relative hyperpig-mentation of the macula. The pigmentation ofskin, hair, and parts of the anterior uveal tractoriginates from melanocytes derived from theneural crest cells and appears at about the 20thgestational week.5 The optic pathways from eyeto chiasma form early, before there is anypigment in the mammalian embryo except forthe retinal pigment and a transient pigmenta-tion of the upper wall of the distal primitive eyestalk.' 1112 In normal embryos, the develop-ment of the optic nerve and chiasmal decussa-tion seems to depend on the development ofmelanin and pigmented cells.' In albinism, thelack of pigment cells and melanin of the retinais thought to play a major role in the misrout-ing of the optic nerve axons at the chiasma.The foveal pigmentation is, in the same way,thought to be essential to the normal develop-ment of the foveal photoreceptors and visualresolution." " Albinos have an optic chiasm,where temporal retinal fibres that normallyshould remain ipsilateral decussate to the con-tralateral side. The relatively larger number offibres decussating compared with the numberremaining on the ipsilateral side will giveasymmetric visual evoked responses (VER)from the ipsilateral compared with the con-tralateral visual cortex after monocular stimu-lation.' 814 It has been claimed that thisincrease in the number of decussating fibrescan be shown with VER with a sensitivity of100% and are pathognomonic for albinism.'4However, asymmetric VER has been detectedin patients with dissociated vertical deviation,"although this finding is controversial.'6 Asym-metric VERs have also been recorded in casesof chiasmal malformations but in the oppositedirection compared with albinism."

Albinoidism refers to another group ofpatients with congenital hypomelanosis butwithout nystagmus, neuronal, or other abnor-mality and with normal or only rarely subnor-mal visual acuity.'

Optic malformations (hypoplasia, atrophy,and coloboma) and retinal dystrophies mayresult in subnormal vision, and in some casesthese anomalies will remain undetected for along time. In other cases low vision can alreadybe detected in the infant (DVM, delayed visualmaturation), although the causes may beobscure. Thus, such conditions (DVM, albi-nism, albinoidism, retinal dystrophies, andoptic malformation) may be very difficult to

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Eye Clinic, MolndalsHospital, Molndal,SwedenL Sjodell

Pediatric Eye Clinic,East Hospital, SwedenA Sjostr6m

Department ofOphthalmology,G8teborg University,Goteborg, SwedenM Abrahamsson

Correspondence to:Dr Lena Sjodell, Eye Clinic,M6lndals Hospital, S-431 80Molndal, Sweden.

Accepted for publication11 March 1996

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diagnose, and can be referred to as subnormalvisual acuity syndromes (SVAS) in children.Since they have a somewhat different progno-sis, and because SVAS may also be the first signof a neuroimpairing condition, it is of greatimportance to be able to diagnose and give aprognosis of the condition. This paper de-scribes such a group of children with SVASwho as a result of subnormal visual acuity werereferred to the eye clinic. They had no obviousclinical signs indicating a particular syndromeor condition, except iris transilluminationwhich suggested an ocular albinism.

Subjects and methodsWe studied children who were referred to theeye clinic in Molndal because of early strabis-mus or subnormal visual acuity at a visualscreening included in a general health controlof all children aged 4 years in Sweden.'8Informed consent from both children and par-ents was obtained for patients and controls.Four children were sent to the eye clinicbecause of subnormal acuity in the test atschool. The inclusion criterion has been iristransillumination, which was recognised at theclinical examination performed when visualacuity did not improve as expected. Apparentnystagmus has been an exclusion criterionsince these children often have an earlydiagnosis of albinism. The aim of this studywas to examine a group of children where themanifestations of possible albinism were moresubtle and to try to find out if an ocularalbinism could explain the subnormal visualacuity. The children were followed clinically for2 to 11 years and they have been treated withglasses and occlusion according to the generalregime in our clinic. No severe ocular malfor-mations or retinal dystrophies were found.The children were called in for a standard

examination. The group included 18 children,five boys and 13 girls, and at the last examina-tion they were aged 6-21 years (mean age 12.4years, median age 12 years). The examinationincluded iris translucency grading, refractionvalues, best corrected visual acuity, assessmentof strabismus and nystagmus, best stereoacuitytested with TNO, Titmus fly or Bagolini, andVER recordings.

VISUAL ACUITYA letter chart at 5 metres distance was used totest the visual acuity. When the child was tooyoung to read letters an tumbling E chart at thesame distance was used. A maximum of twoerroneous identified letters on a single row wasallowed.

IRIS TRANSLUCENCYIris transillumination was accomplished byroutine slit-lamp examination19 with only onedesklamp lit in the otherwise darkened room.The transillumination was graded in thefollowing manner: minimal defects (I), moder-ate defects but lens equator not seen (II), mod-erate defects and lens equator visible (Ill), orobvious defects and lens equator clearly seen(IV). Furthermore, there was an assessment asto whether the transillumination engaged the

periphery of the iris, the centre, or both andhow many quadrants of the iris showed trans-illumination. Two observers made this exami-nation independently in 15 of the 18 patientsto test the reproducibility of the method. Theagreement between the observers was goodand only minor disagreements were seen in afew cases.

REFRACTION, MACULAR EXAMINATION, FUNDUSPHOTOGRAPHYAutorefraction and ophthalmoscopy were per-formed after inducing pupillary dilatation andcycloplegia with cyclopentolate eyedrops.Fundus photography was also included, and

special interest was focused on the macula dur-ing examination of the photographs. Thisexamination was performed independently bythree ophthalmologists. Two observers alsomade an independent assessment of thepigmentation of the fundus. The visibility ofthe choroidal vasculature in the four quadrantsof the fundus and in the posterior pole werescored. A maximal score was 17 points whenthe choroidal vessels were easily seen all overthe fundus and 0 points were scored if thewhole fundus was well pigmented.

VISUAL EVOKED RESPONSE, VISUAL EVOKEDPOTENTIAISFor the VER recordings a visual stimulus of ashort latency light flash of high intensity(supramaximal) was used (Grass PS 22, inten-sity setting 16, duration <100 ps), bi- andmonocularly in each session. Particular atten-tion was paid to accomplish a complete coverof the fellow eye in monocular stimulation.Recordings from five positions- in a horizontalrow at the occipital level'4 were performed(Ola, 01, Oz, 02, 02a). The VER activity wasaveraged (n=20-30) by a Medelec averageoscilloscope, with bandpass filter of 2-200 Hz.The VERs were manually analysed by twoexperienced VER scientists, particularly withrespect to side asymmetries to monocularstimulation.8 14 In each session two series ofrecordings were performed to control consis-tency of the response. The recordings from twosessions were analysed for 10 subjects, andfrom one session for seven subjects. Onepatient did not turn up at any session.

CONTROL SUBJECTSA group of 64 patients (32 boys and 32 girls)served as controls concerning the ophthalmicexamination (refraction, visual acuity, iris trans-illumination, retinal inspection). These wereconsecutive patients sent to us because of sub-normal vision at the 4 year health control men-tioned above or from the school health care.Some of these children have only been to theeye clinic once for examination while othershave been followed and treated with glassesand/or occlusion. At the last examination theywere aged 4-10 years (mean age 6.2, medianage 6 years).Twelve children, 4 to 12 years old, with nor-

mal visual acuity and no iris transilluminationvolunteered for the electrophysiological exami-nation.

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Table 1 Characteristics of study group

Visual acuity Visual evoked potentialSexlyear Fundusof birth 1991 1993 Iris Macula 1992 1993 Stereo Strabismus Iris colour Tan scale 0-17 Treatment

Female/84* 0.6/0.4 0.7/0.5 IV/4c - Sym Sym 60" 1L eso Mixed Slightly tanned 14/13.5 S + 0Female/82 0.5/0.5 0.5/0.4 IV/4c - Not sym Not sym 800' Eso Mixed Red 6.5/6.5 SFemale/79t 0.3/0.5 0.4/0.5 IV/4c - Sym +Bagolini Eso Blue Slightly tanned 7.5/8.0 S + 0Female/77t 0.7/0.5 0.7/0.7 IV/4c - Not sym Titmus 0 Blue Slightly tanned 9.5/11.5 NoneFemale/81 0.6/0.9 0.6/0.9 IV/4 + Not sym Not sym Titmus 0 Mixed Slightly tanned 4.5/3 SMale/81 0.6/0.3 0.6/0.5 IV/4 - ns ns +Bagolini Exo Mixed Slightly tanned 11/12.5 S + 0Female/87* 0.5/0.5 0.6/0.7 IV/4 - Not sym Not sym 60 0 Blue Slightly tanned 16.5/16.0 NoneFemale/73 0.7/0.7 IV/4 - Not sym 240" 0 Blue Tanned 10.0/12.0 NoneMale/76* 0.9/1.0 IV/4 + ns 60" Intermitt exo Mixed Slightly tanned 3.5/3.0 SMale/71 0.7/0.9 IV/2 + 0 Blue Slightly tanned 8.5/8.5 SFemale/83t 0.7/0.9 1.0/1.0 IV/2 + Not sym Not sym 30' 0 Mixed Slightly tanned 4.5/4 S + 0Female/86 0.5/0.4 0.7/0.7 IV/2 + Not sym Not sym 120" 0 Mixed Tanned 1/1 S + FMale/79 0.7/0.9 0.7/1.0 III/3 + ns ns 240" 0 Blue Red 10/8.5 SFemale/81 0.7/0.7 0.9/0.9 III/3 + ns 60" 0 Blue Tanned 4.5/5.5 SFemale/81 0.8/0.5 1.0/0.5 III/i + Sym 40' 0 Blue Slightly tanned 5.5/5.5 SMale/82 0.7/0.7 0.7/0.7 II/2 + Sym Sym Titmus ji eso Blue Tanned 1.5/2 S + 0Female/79 1.0/1.0 1.0/1.0 11/2 + Sym 240" 0 Blue Red 9/7.5 NoneFemale/83 0.8/0.5 0.8/0.6 II/1 + Not sym 60" 0 Blue Red 10.5/10.5 S +O

S=spectacles, O=occlusion, F=filter; II-IV=grade of transillumination; 1-4=number of quadrants engaged by transillumination; c=centre of iris transilluminated;*=sisters, t=sisters, t=cousins; Macula +=OK, -=no foveal reflex; Fundus scale 0 all of fundus pigmented, 17 no pigment in fundus; Sym=symmetric VEP; Notsym=asymmetric VEP; ns=small asymmetry, see text.

STATISTICSCorrelation coefficients were calculated for thedifferent relations between degree of iristransillumination, stereopsis, visual acuity,VER asymmetries, foveal reflex, and visualacuity.

ResultsThe results of the SVAS group are summarisedin Table 1.

VISUAL ACUITY (FIGS 1A AND 1B)The mean visual acuity for the study group was0.73 (range 0.4-1.0) compared with 0.85 forthe control group (range 0.2-1.0). In the con-trol group there are two eyes with acuity below0.6-in the eye with acuity 0.2 the occlusiontherapy was not accomplished, and the eyewith acuity 0.5 was highly myopic (-9 D) andamblyopic in spite of spectacles and occlusiontherapy. Best corrected visual acuity in thebetter eye was 0.8 or more in 50% of patientsin the study group and in 87.5% in thecontrol group.

REFRACTIONThe spherical errors in the study group rangedfrom -5.25 D to +7.5 D; seven myopic eyes, 29hyperopic eyes, but no emmetropic eye. In thecontrol group the range was from -9 D to+6.75 D; 12 myopic, four emmetropic, and1 12 hyperopic eyes. If we disregard the patientwith monocular myopia of 9 D, the most myo-pic eye in the control group was -3.25 D.There was a higher incidence of astigmatism

in the study group. Fifty per cent of thepatients (42% of the eyes) had a cylinder of1-3 D compared with 34% of the patients(25% of the eyes) in the control group.Anisometropia, defined as 1 D difference or

more in the most refracting axis, was morecommon in the study group (50%) than in thecontrol group (14%). If the anisometropia isdefined as 1 D difference or more, in sphericalequivalents the corresponding figures are44.5% and 10.9 % respectively. The frequencyof anisometropia in the control group is higher

than expected in normal individuals. Amongchildren the prevalence is reported to be1.4-4.7%16 17 22 and in an adult population9%,21 but there are differences in the definitionof anisometropia between the authors. Thehigher anisometropia prevalence in our controlgroup is explained by the referral system (seeSubjects and methods).

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Figure 1 (A) Visual acuity of the group with subnormalvisual acuity syndrome (SVAS) (18 children, 36 eyes).(B) Visual acuity of the control group (64 children, 128eyes).

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PIGMENTATION OF SKIN, HAIR, AND IRIDESNormal tan was self reported in four patientswhile a slight tan was self reported in 10patients. In four cases sunlight exposure resultsin a red skin. In the latter case only one patienthad an iris transillumination grade IV in allquadrants. The colour of the irides was blue in11 cases and mixed in seven patients. In nocase was there a brown iris. In the group ofnine patients with grade IV transilluminationin all quadrants there were five patients withmixed iris colour and four with blue irides. Thecolour of the hair was light brown in twopatients both with grade IV transilluminationin two quadrants and a non-symmetric visualevoked potential (VEP) on two occasions. Therest of the patients were fair but not extremelyblond.

IRIS TRANSITLUMINATION (FIGs 2A AND 2B)All eyes in the study group had iris transillumi-nation since this was the inclusion criterion.The grade of transillumination was variablehowever (Fig 2A).Nine children had a marked transillumina-

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quadrants (grade IV). Four of them also hadclear defects in the pigment in the centre of theiris.Three patients had grade IV transillumina-

tion in two quadrants. Three patients hadgrade III and three patients grade II in 1-3quadrants.Only patients with grade IV showed defects

in the centre of the iris. In all patients the iristransillumination was symmetrical in the twoeyes.

In the control group (Fig 2B) 12 individuals(18%) showed some iris transillumination, aseven a minute area of transillumination wasconsidered positive in this study. In blue eyedpatients eight (18%) were positive, in mixedcolour eyed patients three (30%) were positive,and in brown eyed patients one (10%) waspositive. These figures are comparable with thenormal transillumination incidence in a popu-lation described by Jay et al.4 They found anoverall incidence of 9.2% and 19% in blueeyed subjects.

Five individuals had grade I transillumina-tion, one individual grade II, two individualsgrade III, and four individuals grade IV (Fig2B). In the individual with grade II transillumi-nation all quadrants were engaged and this wasalso the case with two individuals with gradeIV. In the other individuals 1-2 quadrants hadtransillumination. All but one individual hadsymmetrical transillumination in both eyes.This individual had grade I transilluminationin one eye and none in the other.

STRABISMUSStrabismus was seen in six patients (33%) inthe study group (Table 1) and in the samenumber in the control group (9%). In the studygroup four children had esotropia, one ofthemis straight with spectacles and has full stereoacuity (60", TNO). Two children had intermit-tent exotropia.Among the control children four had

11/1 11/2 III/1 111/3 IV/2 IV/4 esotropia-one is straight with spectacles, onehad exotropia, and one hypertropia.

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Grade of transilluminationFigure 2 (A) Iris transillumination of the group withsubnormal visual acuity syndrome (SVAS). See textfordetails. II-IVindicate grade of transillumination and 1-4the number ofquadrants engaged by transillumination. Thefour patients with peripheral and central transilluminationare indicated by a stippled area. (B) Iris transilluminationof the control group. See(A) and textfor details.

STEREOPSIS (TABLE 1)Stereoacuity was good: at least 120", in eightchildren in the study group; moderate, 240" inthree children; and bad, Titmus fly and/orBagolini positive in six children (three of themhave esotropia and one intermittent exotropia).One patient was not tested for stereo acuity.

MACULAR EXAMINATIONIn the assessment of the fundi special attentionhas been focused on the macula. In the studygroup seven patients had clearly pathologicalmaculas with an indistinct or absent fovealreflex. Eight patients were considered havingnormal maculas and in one patient all threeobservers considered the right foveal reflexabnormal while the left fovea was considerednormal. In this patient's right eye there is also apigmentation of unknown aetiology close tothe papilla. In two patients the observersdiffered somewhat in their assessment but inthese patients there was no obvious macularpathology. Most of the patients had enough

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pigment in the posterior pole to mask most ofthe choroidal vasculature but in three patientsthe choroidal vessels were easily seen. In thecontrol group all patients' maculas wereconsidered normal at clinical examination.Concerning the pigmentation of the fundusthere were five patients with a score of 11 ormore. They all had a pronounced transillumi-nation of the iris and a pathological macula.The remaining scores did not correlate withiris transillumination or macular pathology.MOTILITY AND NYSTAGMUSNystagmus or motility disorders was not acommon sign (see Subjects and methods) andonly a very subtle nystagmus was noticed intwo patients in the study group. One patienthad rotatory nystagmus seen in the microscopeand the other had an intermittent rotatory nys-tagmus noticed at some appointments.

Figure 4 Visual evoked responses (VERs) showinglocalised asymmetries. Procedures as described in Figure3 and text. The short latency responses are symmetrical.With onset, as indicated by the broken line, a short period ofthe VER shows asymmetry, indicating albinoic visualpathways. This kind of response was recorded in some of thepatients in the study group, but also, as in this figure from aparent. This VER pattern was recordedfrom the mother ofthe patient in Figure 3.

Figure S Fundus photograph ofa patient with normalpigmentation but asymmetric VER.

Figure 3 Visual evoked response (VER) from a patient inthe group with subnormal visual acuity syndrome. Theupper 4 VERs are simultaneously recordedfrom 01(uppermost), Ola, 02a, and 02-that is,from left to rightat the Oz level. Flash light stimulation of the right eye. Thelower 4 VERs are responses after stimulation of the left eye.Note asymmetries and potential reversals after rightcompared with left eye stimulation. Time base 30 ms,amplification barS nV

VISUAL EVOKED RESPONSE (FIGs 3 AND 4,TABLE 1)Typical albinoicVER asymmetry was shown ineight patients (Fig 3); five had symmetricVERs and in four patients VER recordingswere difficult to classify (Fig 4). In this groupthe asymmetry was not as distinct as in thetypical cases. All of the control VERs weresymmetric.Asymmetry was found among those patients

with marked iris transillumination (grade IV)and absent foveal reflex as often as amongpatients with moderate transillumination andnormal macula (Fig 5). Among the patients

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with symmetric VER there were two withmarked transillumination and indistinct fovealreflex.

DiscussionThe present study was initiated to investigateunclear subnormal visual acuity and late visualdevelopment in preschool children and chil-dren in their first school year. In one group wefound iris transillumination as a commondenominator which could suggest an ocularalbinism and thereby explain subnormal visualacuity. We decided to examine this groupfurther. In cases of typical albinism (nystag-mus, absent foveal reflexes, very low visualacuity, absence of stereopsis) the diagnosticdilemma did not occur. The aim of the presentstudy was to evaluate the albino diagnosis inmore subtle cases.We found some signs that could indicate

ocular albinism. A marked iris transillumina-tion and absence of foveal reflex was found inseven patients and this seems to correlate witha subnormal visual acuity (cf Abadi andPascal"2). However we have not been able toprove that these patients are albinos in thesense that they do not all have an asymmetricVERs. On the other hand some patients withless iris transillumination, with a normalmacula, but subnormal visual acuity did showasymmetric VERs. It seems obvious that a highdegree of iris transillumination and ill definedlow pigmented maculae/fovea indicate a lack ofpigmented cells or low pigment content withinpigmented cells. Why such eyes, with clearindications of albinism, do not always have achiasmal abnormality with an increased num-ber of optic axons decussating is unclear.

In previous studies an electrode montageused as in the present work was claimed to benecessary to detect albinism." Others claimthat only a pair of electrodes, bipolarlyconnected symmetrically on each side of theocciput, is sufficient for the diagnosis ofalbinism.2 8 It has also been claimed that insmall children the flash evoked VER is a suffi-cient stimulus to reveal albinism, but that inolder children and adults the pattern onsetmethod is preferred.2!1 However, in thepresent study we recorded albino asymmetriesin both teenagers and older children as well asin smaller children. It was also shown recentlythat, for example, it is possible to record andidentify pattern response after a patterned flashstimulus.22 Even if the cortical activation differswith different stimuli, a powerful flash stimulusprobably activates the main primary visualafferent fibres and cortical neurons.2' 24 Hence,there should be no main afferent fibres silentafter a supramaximal flash, as was used in thepresent study. It should therefore be possible todetect any occipital side differences to mono-cular stimulation, if there are retinocorticalside differences as a result of an albinoicdecussation. The detection level and resolutionof the method depends not only on the stimu-lus, but also on the amplification, displayedtime base, averaging procedures, and filteringof the recorded activity.213 In eight children

typical albino VERs were recorded, as de-scribed by Creel et al 2 8 and Apkarian et al"with no difficulty in classifying them asasymmetric.

In four children, however, we recorded lessbut distinct asymmetries. In a study of twobrothers, Summers et al 25 showed asymmetricVERs in both, but only one had subnormalvision. Both had foveal changes and iris trans-illumination. The VER asymmetry of thebrother with normal visual acuity was less dis-tinct when compared with his brother's VER.This might be explained by a difference in thenumber of optic nerve fibres decussating in theoptic chiasm. It is thus likely that, despitedetailed procedure and apparatus, small asym-metries will not be detected (perhaps unlessrecordings are performed from the optictracts). In our study we had two pairs of sisters(Table 1; patients 1 and 7 and patients 3 and 4)and they all have a pronounced iris transillumi-nation and pathological maculas. However,one sister has an asymmetric VER while theother has a symmetric VER.We also have a pairof cousins (Table 1; patients 9 and 11). Theyboth have a quite pronounced iris transillumi-nation but normal maculae and their VERs aredifferently classified. Another interesting find-ing is that the mother of the child representedin Figure 3 also shows asymmetries, butrestricted to a short time window indicatingalbinism (Fig 4).Because of the anatomy of the visual

pathways classic albinos are considered to lackstereopsis,' but stereopsis is present in manyVER asymmetric albinos.26 Moreover, in thereport by Summers et al,25 the brother with iristransillumination, absence of foveal develop-ment, and asymmetric VER had good visualacuity (20/20) and stereopsis (100", TNO).Four of our eight patients with clear asymmet-ric VERs had good stereopsis (30-120"), onehad fairly good stereopsis (240"), while threehad stereopsis of 800" or less. One of thesethree patients had an esotropia.Bergsma and Kaiser-Kupfer described a

'new' form of albinism' with diffuse, fine,punctate transillumination of the iris, loss offoveal reflex, and mildly reduced visual acuity.They also found a diffuse, punctate depigmen-tation in the retina. VER recordings were notpresented in these patients. Jay et al considerthis form of albinism to be identical to the het-erozygous state of oculocutaneous albinism butthese patients usually have normal visualacuity.4 Our patients are in some ways similarto the patients described by Bergsma andKaiser-Kupfer but the transillumination seemsto be more coarse and they do not all have aloss of foveal reflex. The visual acuity is in therange 0.5-1.0 but as a group the visual acuity isclearly subnormal compared with the controlgroup. In fact, the first inclusion criterion wasthat these children were examined because ofsubnormal visual acuity during the ophthalmicsection of the general health screening in Swe-den at 4 years of age. In our study group thereis a correlation between visual acuity andmacular pathology. The patients with patho-logical maculas had best corrected visual acuity

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in the better eye of 0.5-0.7. For the patientswith normal maculas the corresponding acuitywas 0.7-1.0. If the foveal pigmentation isessential for the normal acuity development'012the lack of macular pigment in these patientscould explain this difference.There are several other plausible explana-

tions for a subnormal visual acuity apart fromalbinism; for example, refractive errors, othermalformations of the eye and optic nerve, reti-nal dystrophies, congenital nystagmus, delayedvisual maturation (DVM), and mental retarda-tion. During the examinations we have foundone possible minor malformation, a pigmenta-tion of unknown aetiology close to the papilla.However, the visual acuity in this eye hasfollowed the fellow eye and is now 1.OWe havealso found clearly indistinct maculas in sevenpatients but this could, or is likely to, be associ-ated with albinism. None of the patients had atypical congenital nystagmus-that is, purelyhorizontal.6 Two patients had a very discreterotatory nystagmus which should not aloneaffect the visual acuity. DVM is a retrospectivediagnosis but the delay and improvement isusually seen during the first or at least duringthe second year of life. All our patients areolder than this but it may exist as other formsof DVM/SVAS which improves later in life.None of the patients in the study group ismentally retarded or otherwise delayed indevelopment.Thus, SVAS seems to be a heterogeneous

condition of high variability, including formswith chiasmal fibre decussation of almost nor-mal rate, 50%, to a maximal decussation of100% of the optic axons. Vision may benormal, despite VER asymmetries. In ourstudy group all had iris translucency as a signof hypopigmentation and low acuity seems alsoweakly correlated with foveal abnormality. Webelieve that our patient group has some sort ofalbinism and that it is worthwhile looking foriris transillumination when visual acuity doesnot improve as expected. The albino diagnosis,with VER recordings if possible, can reassurethe parents and patients that the condition isstationary or might improve and that they donot need to worry about deteriorating visualfunction.

In summary, there is no simple correlation ofthe degree of iris transillumination, stereopsis,visual acuity, and VER asymmetries. Thereseems to be a correlation between marked iristransillumination in all quadrants, absence of afoveal reflex, and low visual acuity (sevenpatients). In this group the visual acuity is 0.5-0.7 in the better eye. Two patients with markedtransillumination in all quadrants but normal

maculae have a visual acuity of 0.9-1.0 in thebetter eye. Patients with less transillumination(grade IV in two quadrants or less) all havenormal maculae and visual acuity in the bettereye 0.7-1.0. Note also that VER asymmetry isnot correlated with absence of stereopsis(Table 1).

This study was supported by The Blinda Vanners Foundation inGoteborg, MargitThyselius Foundation for blind youth,Bohuslandstingets FoU-group, Kronprinsessan Margarethasarbetsnimnd, and Swedish Medical Research Council 02226.

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