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 photographs	Which 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-Khani32	No information	One central and one nasal 50° field per eye.	Red free digital images	No information	No information	International Diabetic Retinopathy and Macula Edema Severity Scales	Performed by specially trained ophthalmic nurses	No information	No information
Jones et al26	Both pupils were dilated with 1% tropicamide drops	Two photographs of each eye were taken, one centred on the optic nerve and the other on the fovea. Images taken by trained retinal screeners	Mixed 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 information	1990–2002: 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 grader	No information
Kohner et al33	Yes	Four-field 30° retinal photographs taken as stereo pairs	No information	No information	No information	Allocated 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 information	Only patients with a set of good quality images of both eyes were included in the study.	No information
Kristinsson et al29	Yes	No information	No information	No information	Yes	No information	No information	No information	No information
Looker et al40	If required	Single field	Digital photograph	No information	Slit lamp outcomes were not available for all patients, but where available, results were used.	Scottish grading system	No information	No information	No information
Maguire et al34	Yes—1% cyclopentolate and 2.5% phenylephrine	Stereoscopic fundal photography of seven fields. Non-simultaneous photographic pairs for each eye	Viewed with a Donaldson Stereoviewer providing a 3D representation of the fundus.	Topcon fundus camera	Yes. 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 al25	As Jones et al
Olafsdóttir and Stefánsson30	Yes		Colour photographs taken with a 90-diopter lens		Yes	Visual 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 al31	No Information	One fundus photograph centred on the macula of each eye taken with 45° non-mydriatic retinal camera	Instant film Polaroid	Canon CR4-45NM	No	International 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.	No	Once for the purpose of this retrospective study
Stratton et al39	Yes	Two standard 45 fields—Macular and disc centred—per eye	Digital colour retinal photographs	No information	No information	Grading 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 venues	Internal and external quality-assured reading process that reaches national recommendations.	No information
Thomas et al1	Tropicamide (applied to each eye 15 min before screening	Two 45° digital retinal images per eye—one macular centred and one nasal field	Non-mydriatic Canon DGi camera			Screening 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 chart		Retinal images transferred to a central reading centre for grading
Younis et al35	1% tropicamide with or without phenylephrine	Three overlapping non-stereoscopic 33 mm transparency photographs of each eye	Either Canon CR4-45NM with 45° fields or a Topcon TRC 50 SX camera with 50° fields.	No information	Patients 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 information	No information	No information
Younis et al36	As Younis 2003b

NSC, National Screening Committee; MA, microaneurysms; STDR, sight threatening diabetic retinopathy.