4.2Methods

We recruited 100 patients consecutively from the DR screening clinic of Royal Perth Hospital (RPH), Western Australia, in 2010. This study has been approved by the RPH Human Research Ethics Committee.

The recruited patients were inquired about their demographics, ocular history, and diabetes history including types, duration, HbA1c level, history of hypertension, hyperlipidemia, smoking status, macrovascular (stroke, myocardial infarction, and peripheral vascular disease), and microvascular (previous history of retinopathy, nephropathy, and neuropathy) complications.

All patients had pupillary dilation using 0.5% tropicamide and 2.5% of phenylephrine and subsequently underwent three sets of examinations including (1) three-field (optic disk, macular, and temporal views) 30° nonstereo retinal color still photography using FF450 plus (Carl Zeiss Meditec, North America, USA), (2) retinal color digital recording using EyeScan (Ophthalmic Imaging System, Sacramento, USA), and (3) slit lamp examination by a senior consultant ophthalmologist using a 78-D handheld lens (reference standard).

Instead of the gold standard Early Treatment Diabetic Retinopathy Study (ETDRS) [4] stereoscopic 30° seven fields, our study selected slit lamp examination by a senior consultant ophthalmologist as the reference standard for our due to a few reasons. For slit lamp examination, it is less timeconsuming, easy to perform, and causes less patients distress due to constant exposure to bright lights/flashes from the retinal cameras. In addition, patients who have moderate to severe cataracts will often have poor quality retinal images, and hence, they will eventually need to be examined under the slit lamp examination by an ophthalmologist.

In view of assessing the usability of this new technique, we recruited an inexperienced medical officer to perform the retinal video recording, whereas FF450 plus was operated by an experienced orthoptist who has had 10 years experience in performing retinal still photography for DR. For retinal video recording, the operator is required to slowly tilt the retinal camera horizontally from optic disk to the macula and temporal

Table 4.1 International clinical diabetic retinopathy severity scale and international clinical diabetic macular edema disease severity scale [5]

views. Each view should approximately last for 5 s for the ease of interpreting DR lesions. The video file format is in a standard Audio Video Interleave (AVI) format which can be easily played by various video media players.

All the retinal digital videos (EyeScan) and color still images (FF450 plus) were randomized and downloaded into two hard disks for interpretation by two consultant ophthalmologists (one with special interest in diabetes and one retinal specialist). All retinal digital videos and color images were viewed on a 27-in. iMac (Apple, USA) in a dimly lit room. In terms of the photographic grading system, the International Clinical Diabetic Retinopathy Severity Scales (Table 4.1) [5] was chosen due to its simple and easy-to-use grading criteria. This grading system was introduced in 2002 with the aim to promote communication between the specialist and nonspecialist personnel in the referral of patients with DR.

Given that a 1-min uncompressed retinal video takes up 1 GB of storage capacity, it will not be practical to be implemented in a routine, mobile, and teleophthalmology setting. As a result, we