Sir,
I read with interest the controversy articles of Yusuf et al and Purbrick and Chong regarding the value of teaching direct ophthalmoscopy to undergraduate students as part of their clinical training.1, 2 Although no ophthalmologist would dispute the importance of fundus assessment per se, I feel most would agree that the direct ophthalmoscope is not the best instrument for the job. Indeed, it is rarely used by many ophthalmologists, myself included. Its most striking weakness that was not touched on by Purbrick and Chong, is the narrow field of view that it affords the user. This is quoted to be around two disc diameters in the emmetropic patient which approximates to 7 mm2 of retina simultaneously in focus. This field of view becomes even smaller in the myopic patient.3 Given that the surface area of the average human retina is 1204 mm2,4 the user of the direct ophthalmoscope would be required to systematically visualize 172 ‘fields of view’ to be certain not to miss a fairly large lesion measuring up to two disc diameters in size. This is of course completely impractical and leads to the inevitable conclusion that even in the hands of the most experienced practitioner, it is simply not possible to comprehensively examine the fundus with the direct ophthalmoscope. Its high magnification, however, makes this instrument ideally suited to assessment of the optic disc for example. While I believe it is reasonable to teach students direct ophthalmoscopy and its indications, it is equally important to emphasise the significant limitations of the technique, namely narrow field of view, monocularity with consequential lack of stereopsis, lack of access to pre-equatorial retina, and poor view through media opacities. With this in mind, our future colleagues practicing in other areas of medicine may have a better understanding of when specialist ophthalmic referral for fundoscopy is appropriate.
References
Yusuf IH, Salmon JF, Patel CK . Direct ophthalmoscopy should be taught to undergraduate medical students—yes. Eye (Lond) 2015; 29 (8): 987–989.
Purbrick RMJ, Chong NV . Direct ophthalmoscopy should be taught to undergraduate medical students—no. Eye (Lond) 2015; 29 (8): 990–991.
Elkington AR, Frank HJ, Greaney MJ . Clinical Optics, 3rd edn. Blackwell Publishing: Oxford, UK, 1999.
Panda-Jonas S, Jonas JB, Jakobczyk M, Schneider U . Retinal photoreceptor count, retinal surface area, and optic disc size in normal human eyes. Ophthalmology 1994; 101 (3): 519–523.
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Orlans, H. Direct ophthalmoscopy should be taught within the context of its limitations. Eye 30, 326–327 (2016). https://doi.org/10.1038/eye.2015.225
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DOI: https://doi.org/10.1038/eye.2015.225
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