Table 1

Differences in screening and grading protocols for detecting diabetic retinopathy

Was mydriasis used?How many and which retinal fields were taken?Photographs or digital retinal photographsWhich cameras were used?Were patients tested using slit lamp (biomicroscopy)What grading protocol was used?Were screeners and graders trained and/or accredited?Was grading quality assured?/ Was grading assessed elsewhere?How many times were images graded?
Agardh and Tababat-Khani32No informationOne central and one nasal 50° field per eye.Red free digital imagesNo informationNo informationInternational Diabetic Retinopathy and Macula Edema Severity ScalesPerformed by specially trained ophthalmic nursesNo informationNo information
Jones et al26Both pupils were dilated with 1% tropicamide dropsTwo photographs of each eye were taken, one centred on the optic nerve and the other on the fovea.
Images taken by trained retinal screeners
Before 2000: colour transparency film
From 2000: digital imaging
Mobile retinal cameras: Canon 45NM or 46NM fundus cameras (Canon UK, Reigate, UK) with 458 fields and Orion Eyecap and DRSS digital imaging software.No information1990–2002: Descriptive grading system based on European guidelines
From 2003: U.K. National Screening Committee grading system
After 2006: NSC grading system
Described as ‘virtually identical’
Before 2000: diabetologist with a specialist interest in retinopathy
From 2000: seven primary graders
Yes. Nationally accredited arbitration graderNo information
Kohner et al33YesFour-field 30° retinal photographs taken as stereo pairsNo informationNo informationNo informationAllocated to a retinopathy severity level using the Early Treatment of Diabetic Retinopathy Study (ETDRS) final scale, modified for four standard fields.
Retinopathy severity categorised as no retinopathy, MA only in one eye, MA in both eyes or more severe retinopathy features.
No informationOnly patients with a set of good quality images of both eyes were included in the study.No information
Kristinsson et al29YesNo informationNo informationNo informationYesNo informationNo informationNo informationNo information
Looker et al40If requiredSingle fieldDigital photographNo informationSlit lamp outcomes were not available for all patients, but where available, results were used.Scottish grading systemNo informationNo informationNo information
Maguire et al34Yes—1% cyclopentolate and 2.5% phenylephrineStereoscopic fundal photography of seven fields. Non-simultaneous photographic pairs for each eyeViewed with a Donaldson Stereoviewer providing a 3D representation of the fundus.Topcon fundus cameraYes. Slit lamp examination of the anterior segment.ETDRS adaption of the modified Ailie House classification of diabetic retinopathy.Graded by an ophthalmologist with a large sample graded by a second grader independently.When necessary, a grading supervisor was used to adjudicate. Agreement between two graders was statistically assessed.No information
Misra et al25As Jones et al
Olafsdóttir and Stefánsson30YesColour photographs taken with a 90-diopter lensYesVisual acuity reported by the better eye.
Retinopathy level determined as the stage of the worse eye.
Visual acuity measured on a Snellen chart at 6 m with the best refractive correction
Screened by an ophthalmologist
Soto-Pedre et al31No InformationOne fundus photograph centred on the macula of each eye taken with 45° non-mydriatic retinal cameraInstant film PolaroidCanon CR4-45NMNoInternational Diabetic Retinopathy and Macula Edema Severity Scales.
Level of disease recorded for the worse eye.
Stored polaroid photographs were graded by the same retina specialist for this study.NoOnce for the purpose of this retrospective study
Stratton et al39YesTwo standard 45 fields—Macular and disc centred—per eyeDigital colour retinal photographsNo informationNo informationGrading based on the ETDRS severity scale
Background retinopathy defined using the R1M0 category on the English NHS Diabetic Eye Screening Programme.
Trained assessors in a central location to the screening venuesInternal and external quality-assured reading process that reaches national recommendations.No information
Thomas et al1Tropicamide (applied to each eye 15 min before screeningTwo 45° digital retinal images per eye—one macular centred and one nasal fieldNon-mydriatic Canon DGi cameraScreening undertaken by a trained photographer
Grading undertaken by trained staff use an enriched version of English National Screening Protocol
Before screening, a trained healthcare assistant assesses visual acuity in both eyes using an illuminated 3 m Snellen chartRetinal images transferred to a central reading centre for grading
Younis et al351% tropicamide with or without phenylephrineThree overlapping non-stereoscopic 33 mm transparency photographs of each eyeEither Canon CR4-45NM with 45° fields or a Topcon TRC 50 SX camera with 50° fields.No informationPatients with ungradable images or STDR invited for slit lamp biomicroscopy by specialists in medical retinal disease.STDR defined as moderate preproliferative retinopathy or greater and/or significant maculopathy in any eye.
Graded by trained graders with a modified Wisconsin algorithm.
No informationNo informationNo information
Younis et al36As Younis 2003b
  • NSC, National Screening Committee; MA, microaneurysms; STDR, sight threatening diabetic retinopathy.