Comparison of non-mydriatic retinal photography withophthalmoscopy in 2159 patients: mobile retinal camera study

Roy Taylor, Lilian Lovelock, W Michael G Tunbridge, K George M M Alberti,Robert G Brackenridge, Peter Stephenson, Eric Young

Royal Victoria Infirmary,Newcastle upon TyneNE14LPRoy Taylor, FRCP, seniorlecturer in medicineLiliati Lovelock, DCR, retinalphotographer

Newcastle GeneralHospital, Newcastle uponTyne NE4 6BEW Michael G Tunbridge,FRCP, consultant physician

Freeman Hospital,Newcastle upon TyneNE7 70NK George M M Alberti,FRCP, professor, department ofmedicine

Hexham General Hospital,Hexham, NorthumberlandNE46 1GJRobert G Brackenridge,FRCP, consultant physician

Queen Elizabeth Hospital,Gateshead, Tyne and WearNE9 6SXPeter Stephenson, FRCP,consultant physician

Ashington GeneralHospital, Ashington,NorthumberlandNE63 OSAEric Young, FRCP, consultantphysician

Correspondence to:Dr R Taylor, VisitingProfessor, Divisionof Endocrinology,Department of InternalMedicine, Yale MedicalSchool, 333 Cedar Street,New Haven, Connecticut06510-8056, United States.

BrMedj 1990;301:1243-7

AbstractObjective-To determine whether non-mydriatic

Polaroid retinal photography was comparable toophthalmoscopy with mydriasis in routine clinicscreening for early, treatable diabetic retinopathy.Design-Prospective study of ophthalmoscopic

findings according to retinal camera screening andophthalmoscopy and outcome of referral to ophthal-mologist.

Setting-Outpatient diabetic clinics of threeteaching hospitals and three district general hos-pitals.Patients-2159 Adults selected randomly from the

diabetic clinics, excluding only those registered asblind or those in wheelchairs and unable to enter thescreening vehicle.Main outcome measures-Numbers of patients

and eyes correctly identified by each technique asrequiring referral with potentially treatable retino-pathy (new vessel formation and maculopathy)and congruence in numbers of microaneurysms,haemorrhages, and exudates reported.Results-Camera screening missed two cases of

new vessel formation and did not identify a further 12but indicated a need for referral. Ophthalmoscopymissed five cases of new vessel formation andindicated a need for referral in another four for otherreasons. Maculopathy was reported in 147 eyes withcamera screening alone and 95 eyes by ophthalmo-scopy only (X2 =11-2 p<0001), in 66 and 29 ofwhich respectively maculopathy was subsequentlyconfirmed. Overall, 38 eyes received laser treatmentfor maculopathy after detection by camera screeningcompared with 17 after ophthalmoscopic detection(X2=8-0; p<0-01). Camera screening underestimatednumbers ofmicroaneurysms (x2= 12-9; p<0 001) andhaemorrhages (X2=7-4; p<001) and ophthalmo-scopy underestimated hard exudates (X2=48-2;p<O.OOl).Conclusions-Non-mydriatic Polaroid retinal

photography is at least as good as ophthalmoscopywith mydriasis in routine diabetic clinics in identify-ing new vessel formation and absence of retinopathyand is significantly better in detecting exudativemaculopathy.

IntroductionDespite the availability of effective treatment dia-

betic retinopathy remains the commonest cause ofblindness among the working population of the UnitedKingdom.' 2 The major problem remains that ofidentifying retinopathy before the onset of visualimpairment as treatment at later stages is largely in-effective.3 Retinal screening of all people with diabetesis therefore of great importance.

Several different methods of screening are in currentuse: ophthalmoscopy by consultants or junior physi-cians in the setting ofa diabetic clinic is the most widelyused method3; systems of liaison with ophthalmicopticians have been set up in some districts.4 Referral

to an ophthalmologist is an expensive option which isnot feasible owing to the large numbers of people withdiabetes.' The recent introduction of retinal camerasable to photograph the retina through undilated pupilswas initially hailed as a useful method of screening, andseveral small studies showed its applicability.6`' Theuse of non-mydriatic cameras for screening, however,has been subject to much criticism, and an impressionof controversy has been created.'0 Any controversymay be more apparent than real as the protagonistshave been arguing about practical usefulness of thetechnique for screening67 whereas the antagonists havebeen arguing about poor performance compared withthe gold standard technique of fluorescein angio-graphy.9 10 Screening techniques cannot be expected toperform as well as detailed investigative techniques butmay appropriately be compared with each other. Therewas therefore a need for a single clearly definedquestion to be answered before non-mydriatic retinalphotography could be accepted as a screening tool:Is non-mydriatic retinal photography as good as oph-thalmoscopy with mydriasis when performed in thesetting of a routine clinic?To answer this question in a generally applicable

manner it was necessary to perform the comparison in alarge number of patients in more than one clinic. Amobile camera unit was designed and used to evaluatescreening methods in three clinics in district generalhospitals and three in teaching hospitals over twoyears.

Patients and methodsPATIENTS

Table I shows the characteristics of the study popu-lation. A total of 4312 eyes in 2159 patients werephotographed. The patients were selected at randomfrom the clinic list; only those in wheelchairs or whowere registered as blind were excluded, and hencepatients aged 12 to 89 years and with a duration ofdiabetes ranging from 0 to 60 years were studied. Mostwere white.

THE MOBILE UNIT

A transit ambulance donated by Northern RegionalHealth Authority was converted to allow transversemounting of a Canon CR3-45NM camera on a motor-ised table immediately behind the driving compart-ment. No suitable commercially available vibrationproof mounting for the camera was available, and adevice was custom built, consisting of high densityfoam blocks held within a steel frame bolted to thefloor. In transit the camera was allowed to float on thefoam pads and in operation it rested on the motorisedtable. This device has proved successful in that the unithas been operating for three years and a distance ofabout 15 600 km has been driven without damage tothe camera. A blackout curtain was placed to separatethe camera from a small waiting area containing twobench seats. All windows were covered and 40 wattred lighting was installed. An electrical supply was

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TABLE i-Clinical and biochemical characteristics of2159 patients and ofgroups with new vesselformation or maculopathy as reported by retinalcamera screening or ophthalmoscopy. Unless specified otherwise values are medians (ranges)

New vessel group Maculopathy group

Camera screening Ophthalmoscopy Camera screening OphthalmoscopyCharacteristic All patients (n=43) (n=50) (n= 157) (n=97)

Age (years) 60 (12-89) 59 (28-82) 59 (25-78) 63 (20-84) 64 (26-82)Duration of diabetes (years) 9(0-70) 16(4-67) 21 (4-67) 13(3-66) 15(0-70)Systolic blood pressure (mm Hg) 140 (86-270) 150 (110-222) 140 (117-197) 150 (101-229) 150 (105-235)Diastolic blood pressure (mm Hg) 80 (53-140) 84 (61-109) 80 (69-104) 80 (65-118) 80 (62-140)HbA1 (%)* 8-3 (4-0-17-5) 8-8 (4-8-14 5) 8-8 (5-0-17-5) 8-3 (4-0-16-0) 8-2 (4-8-15-3)Serum cholesterol (mmoU/l) 6-0 (3-0-11-9) 6-0 (3 4-9-0) 6-2 (4 4-7 9) 6-4 (3-1-11-9) 6-4 (4-0-11-9)Serum creatinine (VmolUl) 87 (37-677) 93 (56-248) 89 (52-260) 94 (69-677) 99 (55-343)No (%) with visual acuity 6/12 or better 1619 (75-0) 22 (50-7) 23 (45-5) 83 (52-9) 41 (42-2)No (%) treated with insulin 1092 (50-6) 25 (58 3) 41 (82-1) 78 (49 7) 50 (51-6)

*Reference range 5-0-7-5%.

provided by cable connection from a socket on the sideof the ambulance to outdoor sockets mounted on thehospital wall close to the outpatient clinics.

STUDY FORMAT

A common approach was agreed among all sixparticipating centres. Groups of four patients at a timewere taken to the unit before medical consultation.Visual acuity was checked with an illuminated 3m

Standard form for recording ophthalmological findings and patient data

Schnellen chart (Rayner Optical Company) and thenone eye per patient was photographed, allowing timefor the consensual response to fade before the secondeye was photographed. Polaroid 779 film was usedthroughout the study. Each batch of four patientswas dealt with in about 20 minutes; thereafter theyreturned to the waiting room and mydriatic drops wereinstilled. Ophthalmoscopy was performed as part ofthe routine consultation by the doctor who wouldordinarily have seen the patient. A standard form wascompleted, which included sketches of each retina(figure). No specific training in funduscopy was given.Biochemical data were entered on to the form as soon asthey were available, and the form was collected by thephotographer.The retinal photographs were not seen by staff in the

clinic but were retained in the screening unit. Theywere subsequently reported in batches by one of threeconsultant physicians using a similar proforma to thatin the figure but including scores for "poor film" and"macula not visualised." A poor film was defined as onein which the entire area of retina photographed couldnot be clearly seen and macula not seen as a film inwhich the area within one disc diameter of the maculalacked clarity. The second category was adopted asfilms taken through a constricted pupil tend to exhibita characteristic darkness around the macula.

Criteria for referral were agreed with the localophthalmologists as: (a) presence of new vessels;(b) preproliferative retinopathy; (c) exudative maculo-pathy; and (d) presence of lesions within one discdiameter of the macula.

CONSISTENCY OF REPORTING OF FILMS

In a preliminary exercise 30 films were reported byall three observers. Counts of haemorrhages and hardexudates agreed to within five lesions in 23 and 22 casesrespectively, but one observer consistently reportedmore microaneurysms. Of three cases of maculopathy,one was correctly classified by all observers and twowere identified by two observers. This exercise allowedagreement on definition and terminology. To allowassessment of observer consistency during the last12 months of reporting of the films in the studyeight unmarked "quality control" films were insertedinto batches for reporting on five occasions eachper observer. The mean intraobserver consistency ofcounting lesions to within one band (<1, 2-5, 6-10,11-20, and >21) was 89-2% for haemorrhages, 90 8%for hard exudates, and 80-0% for microaneurysms.When maculopathy was present the mean detectionrate was 87 0% and when new vessels were present itwas 100%.

ANALYSIS OF DATA

A computer database was constructed from thepaired forms for each patient and was used to deriveinformation on the comparability of the two methods.Information on referral to an ophthalmologist andany subsequent treatment was obtained from clinical

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Name: Hospital:Case number:Date of birth:

Date of examination:Year of diagnosis:IDD (1)/NIDD (2)

BP systolicdiastolicHBA1

Serum cholesterolSerum creatinine

Visual acuity RL-

R L

Number of lesions:(if >20 write 21) R L

CataractMicroaneurysm

0 Haemorrhagex Hard exudate

, Soft exudate (cotton wool spot)| New vesselsV Venous abnormalityL Laser scars

Exudative maculopathy (1=present; 0=absent)Refer to ophthalmologist (1 =yes; 0=no)Observer (consuftant 1; clinical assistant 2;senior registrar 3; registrar 4; senior house officer 5):

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records. In those patients in whom potentially seriousretinopathy had been identified by camera screeningbut had been missed clinically the consultant con-cerned was notified to allow the patient to be referred.The sensitivity of detection for each technique wasdefined as true positives/(true positives+false nega-tives). Specificity of detection was defined as truenegatives/(true negatives+false positives). Data arepresented as mean (SD) and statistical analysis wasperformed with McNemar's test."

ResultsNEW VESSELS

Forty eyes with definite new vessel formation weredetected in the study (table II), of which 17 weredetected by both techniques, 14 were missed bycamera screening, and nine were missed by ophthalmo-scopy (x2= .-2; NS). In the 14 cases ofapparent failuresof detection by camera screening nine of the films werescored as poor, advanced diabetic eye disease wasreported in 10 films without specific identification ofnew vessels, and no film had been obtained for one eyeowing to advanced disease changes. Two cases of truefailure of detection by camera screening occurred, thisbeing defined as overall failure of the technique totrigger referral in the presence ofnew vessel formation.In one case new vessels were clearly visible on review-ing the film, the failure having occurred at the time ofreporting, and in the other no new vessels could beseen. Of the nine eyes in which new vessel formationwas missed by ophthalmoscopy, four were scored asrequiring referral for other reasons and in five thevessels had been missed for no obvious reason.

Overall sensitivity and specificity cannot be calcu-lated as the study was designed as a comparison and didnot include a gold standard. However, within thepopulation reported to have new vessels by any method(n= 118 eyes) the sensitivity of the camera in detectingnew vessels was 65 0% compared with that of 77 5%for ophthalmoscopy. The specificity of diagnosis of

TABLE II-Numbers of eyes with new vessel formation reported with retinal camera screening alone orophthalmoscopy alone, or both, and numbers in which finding was confirmed by ophthalmologist. (To reflectoverall management outcome for each technique numbers ofeyes scored for referral without mention ofnewvessels and of those with new vesselformation which were not referredfor ophthalmological assessment (truemissed new vessels) are included)

Eyes with Eyes with Eyes scored for Eyes withreported confirmed new referral but new missed

Technique new vessels vessels vessels not seen new vessels

Ophthalmoscopy alone 61 14 5 4Camera screening alone 40 9 12 2Ophthalmoscopy and camera screening 17 17 -

Total 118 40

TABLE III-Numbers of eyes with m4aculopathy reported with retinal camera screening alone orophthalmoscopy alone, or both, and numbers in which finding was confirmed by ophthalmologist, accordingto treatment by photocoagulation. (Numbers for which screening diagnosis was not confirmed byophthalmologist and those not referred for any reason are also shown)

Maculopathy Maculopathyconfirmed and confirmed but Maculopathy Not

Technique Total treated not treated not confirmed referred

Ophthalmoscopy alone 95 17 12 55 11Camera screening alone 147 38 28 52 29Ophthalmoscopy and camera screening 66 33 16 17 0

new vessel formation with the camera was 60 3% andthat for ophthalmoscopy was 39 7%.The presence of new vessels arising from the optic

disc was detected and confirmed in 16 eyes. In 10 newvessels were detected by both methods, in three theywere missed by the camera, and in three they weremissed by ophthalmoscopy.

MACULOPATHY

Maculopathy was reported in 208 patients (308 eyes)by either or both techniques (table III). The cameradetected maculopathy not identified with ophthalmo-scopy in 147 eyes compared with 95 eyes in whichmaculopathy was detected by ophthalmoscopy alone(X2=IIl2; p<0 001). A further 66 eyes were identifiedas having maculopathy by both techniques, of which49 were confirmed as having maculopathy and 33received laser treatment. Thirty eight eyes receivedlaser treatment because of camera screening alonecompared with 17 eyes because of screening byophthalmoscopy alone (X2=8-0; p<0 01). For 29 eyeswith maculopathy reported on camera screening areferral for specialist opinion was not made, and hencethese data underestimate the performance of camerascreening.The designation of maculopathy at screening

was confirmed by an ophthalmologist as being trueexudative maculopathy in 45% of eyes (n=66) onreferral after camera screening alone and in 39% ofeyes(n=29) on referral after ophthalmoscopy alone. Therest of the cases were accounted for by lesions beingpresent but not close enough to the macula to beclassed as maculopathy and also by degenerativechanges, including drusen degeneration. Among thepopulation reported to have exudative maculopathy(n=308), camera screening exhibited a sensitivity of74-2% compared with 57 4% for ophthalmoscopy;the respective specificities were 55*3% and 67 0%.Confirmation of diagnosis of exudative maculopathywas not always followed by laser treatment, and thisreflected varying degrees of severity as well as differingophthalmological practices. Of the 66 eyes in whichmaculopathy was detected by both techniques (tableIII), six exhibited changes too advanced to benefit fromlaser treatment.

BACKGROUND RETINOPATHY

In all, 2558 eyes (59-3%) or 1066 patients (49 4%)were reported as free of any diabetic lesion by bothtechniques. Camera screening alone reported 3046(70 6%) eyes as normal and ophthalmoscopy alone3111 (72- 1%). Table IV shows the reporting of micro-aneurysms, haemorrhages, and hard exudates by eachtechnique. Camera screening underestimated by morethan 10 the numbers of microaneurysms (x2= 12 9;p<OO001) and haemorrhages (x2=7 4; p<0 01) moreoften than did ophthalmoscopy, but the reverse wastrue for hard exudates (X2=48 2; p<0 001).

GRADE OF STAFF

Table V shows the number of eyes seen by eachgrade of staff for which a discrepancy of more than10 lesions was reported. All grades except seniorhouse officers tended to report more microaneurysmsand haemorrhages with ophthalmoscopy than photo-graphy, and all grades tended to report fewer

TABLE Iv-Relative performance ofeach techniquefor specific lesions. Figures are numbers ofeyesfor which one technique reported 3-10 or over 10more lesions than the other. Numbers represent previously defined computer banding ofcounts of lesions

Microaneurysm Haemorrhage Hard exudate

Discrepancy Camera screening Ophthalmoscopy Camera screening Ophthalmoscopy Camera screening Ophthalmoscopy

3-10 236 267 102 117 157 116>10 65 113 30 55 124 36

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TABLE V-Effect of grade of observer on number of eves for which a discrepancy of >10 lesions was reported between camera screening andophthalmoscopy

Microaneurysms Haemorrhages Hard exudatesNo of -

Grade of observer eyes Camera screening Ophthalmoscopy Camera screening Ophthalmoscopy Camera screening Ophthalmoscopy

Consultant 1460 27 49 15 30 50 17Clinical assistant 502 5 3 1 6 6 3Senior registrar 652 5 22 5 5 17 7Registrar 1178 18 33 6 1 3 37 7Senior house officer 420 10 6 3 1 14 2

hard exudates with ophthalmoscopy (ratios of camerareporting to ophthalmoscopy reporting more: 2-9, 2-0,2-4, 5-3, 7-0 for consultants, clinical assistants, seniorregistrars, registrars, and senior house officers respec-tively).The percentage of the total number of important

reported lesions corroborated by the camera reportvaried according to grade of staff. For maculopathyconfirmation occurred in 62-9% for consultants, 44-4%for clinical assistants, 50 0% for senior registrars,35 6% for registrars, and 25 0% for senior houseofficers. For new vessels, confirmation occurred in39-1% for consultants, 23-1% for clinical assistants,22 2% for registrars, and 25% (n= 1) for senior houseofficers. No cases of new vessel formation occurredamong those patients seen by senior registrars.

POOR FILMS

A total of433 films (10 0%) were reported as poor, ofwhich 93 (2 2%) were associated with cataracts and 196(4 5%) with small pupils. The presence of small pupilswas scored by the operator before photography, andhence these poor films were potentially avoidable,leaving 5 5% as unavoidable poor films. Two hundredand eight films were scored as macula not seen, 21 ofwhich were associated with cataracts and only 61 ofwhich with small pupils. This appearance was seenpredominantly (71%) in right eyes, reflecting theunplanned tendency to phQtograph left eyes first andhence the residual consensual response in the othereye. Judgment of when the consensual response hadfaded adequately was thus less easy than had beenpredicted. Small pupils were scored only before anyphotography and hence were not reported as effects ofconsensual pupillary constriction.

DiscussionThe results of this study indicate that non-mydriatic

Polaroid retinal photography is at least as good asfunduscopy with mydriasis performed under routinediabetic clinic conditions in detecting new vesselformation. It is superior in detecting maculopathy.These conclusions were reached despite the doctors inthe clinic knowing that their performance was beingevaluated and despite the photographs being assessedin large batches as an extra late evening duty bythe three observers. However, non-mydriatic photo-graphy cannot be assumed to be automatically superioras it is dependent upon the skill of the camera operator.It is a simple matter to take correctly aligned, focusedretinal photographs of a normal eye, but experience isrequired to deal with cataracts, disordered fundi, andpeople less able to comply with instructions. Theproportion of technically poor films in this study waslower than the 17 3% reported by Jones et al, and thismay reflect their use of several photographers withouta special interest in retinal screening.' In routinepractice, now that the study has been completed, thenumber of poor films has been halved because of use ofmydriatic drops before photography if pupils are notedto be too small by the camera operator. In addition,analysis of data from the study showed a need forparticular care in allowing the consensual response to

fade completely, and the number of films exhibiting ashadow in the region of the macula has subsequentlyfallen. In our current practice use of a short actingmydriatic (tropicamide) is indicated only in about 5%of patients. Although routine mydriasis may be arguedto produce better photographs, the use of such eyedrops is not popular with patients, especially those whowill return to work after being screened.The relatively poor performance of all grades of

doctor in detecting maculopathy is interesting and wasnoted in other studies.3 Only 49 eyes were treated formaculopathy as a result ofophthalmoscopy whereas 70were treated as a result of photography. This differenceis all the more striking as for some eyes reported asexhibiting maculopathy a referral for an ophthalmo-logical opinion was not made, maculopathy not beingan outcome parameter in the original protocol. Themacular region is sometimes difficult to examineadequately by ophthalmoscopy because of reflection oflight and discomfort in the patient. In addition, lesionslateral to the macula may be missed because theexaminer's head needs to move across the subject'sface, disturbing visual fixation. The underreporting ofhard exudates by ophthalmoscopy is probably relatedto this as these lesions typically occur in the posteriorpole of the eye. Qualitative inspection of the diagramssketched by the doctors in the clinic suggested that theexcess of haemorrhages and microaneurysms reportedby ophthalmoscopy was a consequence of full examina-tion of the retina nasal to the optic disc, a characteristicsite for these lesions. It seems likely that many doctorsregard the optic disc as the anatomical centre of theretina and use it as a reference point in quartering theretina in the search for lesions. This carries theinevitable consequence that the retina lateral to themacula (one half of the total retinal area) will beexamined poorly.

Analysis of the number of confirmations ofimportant ophthalmoscopic findings on camera screen-ing suggests that consultants performed marginallybetter than senior registrars, clinical assistants, andregistrars. Senior house officers performed notablyworse than other non-consultant staff. This did notbias the comparison between the two techniques asfairly small numbers of examinations were performedby senior house officers, and it must be considered thattheir participation in clinic screening is widespread inthe United Kingdom. Experience did not conferinfallibility, five of the nine cases of missed new vesselformation by ophthalmoscopy concerning consultants.The variability in opinions reported for ophthalmo-logists suggests that the technique cannot be regardedas a gold standard even in expert hands.3

It is apparent from the results in tables II and III thatin only a proportion of patients referred as havingpossible new vessel formation or exudative maculo-pathy was the condition confirmed on subsequentreferral to an ophthalmologist. The specificity ofophthalmoscopy was particularly poor for detectingnew vessels (39%), but it must be considered that thismay reflect awareness of being assessed on the part ofthe clinic doctor as well as relative unfamiliarity withrecognition of new vessels. Referral of such falsepositive findings will tend to increase the real cost of a

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screening programme, but setting referral criteria forclinical practice must reflect both the skill of thescreener so that the rate of missed lesions is low andalso the capacity of the local ophthalmology depart-ment.The routine measurement of visual acuity as part

of any screening programme must be emphasised.Macular oedema may be present without exudateformation and hence would be undetectable on a singlefilm as opposed to stereo photographs of the fundus.'2A fall in visual acuity is a most important indicator ofmacular oedema, and, although no provision forassessing serial change in visual acuity was incorpo-rated into this study, it must be considered an essentialpart of establishing a clinical service.One of the major concerns about non-mydriatic

photography has been that important lesions may lieoutside the 450 field examined and may be missed.8This was not observed in the 4312 eyes examined inthis study, but none the less it remains a theoreticalsource of error for this screening technique. A secondmajor concern of critics of the technique was that newvessel formation would be missed, the new vesselsbeing anterior to the plane of photographic focus. Thiswas found not to be the case, new vessels being missedin only two eyes other than when advanced diabetic eyedisease had made photography difficult. In such casesnew vessels were always evident from inspection of thephotograph, and most of the patients concerned werealready under ophthalmological review. We observedduring initial evaluation of the camera that new vesselsarising from the disc may sometimes be hidden owingto back reflection of light from the disc, and because ofthis we carried out a small initial evaluation ofhow wellthe technique performed on a series of 12 patientsabout to have laser treatment.'8 New vessels arisingfrom the disc were not apparent in one case. In themain study disc new vessel formation was missed inequal numbers of patients by camera screening and byophthalmoscopy, 10 cases being correctly detected byboth.

For a limited period before the study started andafter it finished an evaluation of the impact of avail-ability of Polaroid photographs in the clinic waspossible. The educational effect for both junior staffand senior staff of seeing the disposition of lesionsmissed by initial ophthalmoscopy was considerable.Teaching of ophthalmoscopy to medical students inthe clinic was revolutionised. In some patients re-assurance was provided by showing the actual appear-ance of lesions previously imagined to be worsewhereas in others the vital importance of need forspecific treatment or tighter control was graphicallyclarified. The utility of a photographic record ofprevious retinal appearances in the clinical notes wasgreater than expected, allowing a more confidentdecision to refer or not. The darker, pigmented fundiof Indian patients were shown to be examinable bynon-mydriatic photography just as effectively as inwhite patients.4The cost of this method of screening for and

recording diabetic retinopathy must be considered.The Polaroid film alone costs about £1 per pair of eyes.Depreciation on the capital cost of the camera (£10 500over six years); salaries of the camera operator and thedriver; and vehicle maintenance, insurance, and petrolcosts must be taken into account. If a modest weekly

throughput of 150 patients and a 48 week year isassumed the total cost per patient is £2.92. Use ofPolaroid retinal photography is often discussed inrelation to screening by ophthalmic opticians. The costto the Department of Health is £10 for screening byan ophthalmic optician. Assessment of the cost ofscreening in the hospital clinic must take account of thetime necessary to perform comprehensive funduscopywith mydriasis and of maintaining adequate darkroomfacilities. Limitation of time and facilities has fuelledthe search for alternative methods of screening.

In conclusion, non-mydriatic retinal photography isas good as funduscopy with mydriasis in routine clinicsin detecting new vessel formation but is superior indetecting maculopathy. The educational effect andaudit function of having Polaroid photographs avail-able in the clinic make the technique particularlyuseful for centres concerned with postgraduate andundergraduate training. Non-mydriatic retinal photo-graphy may be used purely as a screening technique bydoctors who do not perform ophthalmoscopy oftenenough to maintain the skill, such as those in generalpractice. However, these conclusions apply onlywhen the technique is used by a trained operator.

The vibration proof camera support was developed by MrRobert Gillon and colleagues in the department of medicalphysics, Royal Victoria Infirmary, and the ambulance conver-sion was carried out by the Newcastle ambulance body shop.We thank the outpatient staff in each hospital for theircooperation, Professor A L Crombie and Mr K Stannard fortheir ophthalmological advice, Dr P D Home, FreemanHospital, for his cooperation, Dr J D Matthews for statisticaladvice, Mrs Christine Hamilton for entry of the computerdata, and the medical records departments for their help. Thedatabase program was written and operated by Mr N DHamilton, department of medicine. The project was financedby the British Diabetic Association.

I Department of Health and Social Security. Blindness and partial sight inEngland 1969-1976. London: HMSO, 1979. (Reports in public healthsubjects, No 129.)

2 Ghaffour IM, Allan D, Foulds WS. Common causes of blindness and visualhandicap in the west of Scotland. BrJ7 Ophthalmol 1983;67:209-13.

3 Sussman EJ, Tsiaras WM, Soper KA. Diagnosis of diabetic eye disease.JAMA 1982;247:3231-4.

4 Burns-Cox CJ, Hart JDC. Screening of diabetics for retinopathy by ophthal-mic opticians. BMJ 1985;290:1052-4.

5 Scobie IN, MacCuish AC, Barrie T, Green FD, Foulds WS. Seriousretinopathy in a diabetic clinic: prevalence and therapeutic implications.Lancet 1981;ii:520-1.

6 Ryder REF, Vora JP, Atiea JA, Owens DR, Hayes TM, Young S. Possiblenew method to improve detection of diabetic retinopathy: Polaroid non-mydriatic retinal photography. BMJ 1985;291:1256-7.

7 Williams R, Nussey S, Humphry R, Thompson G. Assessment of non-mydriatic fundus photography in detection of diabetic retinopathy. BMJ1986;293: 1140-2.

8 Rosen ES, Raines M, Hancock R. Use of nonmydriatic cameras to screendiabetic patients for retinopathy. Seminars in Ophthalmologv 1987;2:37-44.

9 Jones D, Dolben J, Owens DR, Vora JP, Young S, Creagh FM. Non-mydriatic polaroid photography in screening for diabetic retinopathy:evaluation in a clinical setting. BMJ7 1988;2%:1029-30.

10 Taylor R. Non-mydriatic photography and diabetic retinopathy. BMJ 1988;296:1602.

11 Armitage P, Berry G. Statistical methods in medical research. 2nd ed. Oxford:Blackwell, 1987.

12 Kinytoun J, Barton F, Fisher M, Hubbard L, Aiello L, Ferris F. Detection ofdiabetic macular edema. Ophthalmology 1989;96:746-5 1.

13 Taylor R, Lovelock L, Alberti KGMM, Tunbridge WMG. Northern regiondiabetic retinopathy screening project: preliminary report. Diabetic Med1987;4:576A.

14 Mohan R, Kohner EM, Aldington SJ, Nijhar I, Mohan V, Mather HM.Evaluation of a non-mydriatic camera in Indian and European diabeticpatients. Br_7 Ophthalmol 1988;72:841-5.

15 Rogers D, Bitner-Glindzincz M, Harris C, Yudkin JS. Non-mydriatic retinalphotography as a screening service for general practitioners. Diabetic Med1990;7:165-8.

(Accepted 11 September 1990)

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