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Ophthalmic surgery is well suited to the use of telemedicine in diagnosis and management,1,2 but diagnostic accuracy and reliability are critical if it is to be widely introduced.3 Moorfields Eye Hospital is located in central London and runs community outreach clinics. One clinic and operating list in Ealing is 17 miles from the central hospital. The surgical teams operate in Ealing and then return to the central hospital. We therefore investigated the use of a telemedicine link for review of postoperative cataract surgical patients aiming to assess what can be seen clearly and reliably using telemedicine and to identify what the observer using this link may potentially miss.
This study had Moorfields Eye Hospital research and ethics committee approval. Patients consecutively admitted for cataract surgery were recruited to the study and full informed written consent was obtained. A telelink of a pair of Global Telemed mobile workstations connected by three ISDN lines, with a video transmission rate of 384 bit/s was used for examinations,1 with high resolution examination being achieved by static images. Two surgeons conducted examinations, one using the slit lamp and the other using the telemedicine link. Slit lamp signs graded by the two observers comprised the presence and degree of the following—central corneal oedema, corneal oedema at the limbal section, Siedel's sign, folds in Descemet's membrane, anterior chamber depth, flare and cells, intraocular lens decentration, and lens stability. Both observers in person independently examined a group of postoperative cataract patients in order to determine agreement between practitioners.
Twelve consecutive postoperative cataract patients were recruited to the study with 10 others as a control group to assess interobserver agreement by in-person examination. The results of the study are given in Table 1.
Although interobserver variation means that telelink reliability cannot be precisely calculated in terms of sensitivity and specificity, these findings give an indication of the accuracy of slit lamp examination after cataract surgery using 384 K bandwidth. Examination by video telelink was relatively reliable in detecting oedema at the central cornea but did not consistently detect oedema at the corneal section, or anterior chamber flare and failed entirely to detect DM folds or anterior chamber cells. Patients enjoyed the telemedicine experience finding it reassuring to see as well as interact with their surgeon via the telelink.
Video compression algorithms used in streaming video are “lossy” and higher bandwidth increases video quality. The process begins with a good video source with low noise, since noise does not compress well. A poor quality video image is very difficult to stream successfully because of this difficulty in compression. The videoconferencing standard H-261 was implemented to provide for video compression to a given ISDN bandwidth. With increasing bandwidth there is correspondingly better quality video. A televideo link for corneal assessment in Canada using six ISDN lines (768 K) was found to be acceptable, whereas three lines (384 K) were unacceptable (personal communication, Dr M Pop, Montreal, Canada).
The video display also affects the information observed. Broadcast video monitors are accurately colour calibrated, whereas digital compressed video to 384 K bandwidth has reduced colour depth.4 Recognition of corneal oedema is less about well defined structure as subtle display of colour and “haze.”
It is felt by the authors that telemedicine is a wholly different experience from a simple telephone conversation and for many situations is capable of facilitating postoperative assessment with trained operators. H-261 video at 384 K (triple ISDN) is sufficient for anterior segment overall examination but is not sufficient for detailed corneal assessment. Other practitioners have used data rates up to four times faster for more detailed examination.5
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