Year : 1979 | Volume
: 27 | Issue : 3 | Page : 35--36
Direct ophthalmoscopy in very high degree of myopia
RK Mishra, Vijay Kumar, RG Bajaj, S Verma
Medical College, Jabalpur (M.P.), India
R K Mishra
Department of Ophthalmology, Jabalpur (M.P.)
|How to cite this article:|
Mishra R K, Kumar V, Bajaj R G, Verma S. Direct ophthalmoscopy in very high degree of myopia.Indian J Ophthalmol 1979;27:35-36
|How to cite this URL:|
Mishra R K, Kumar V, Bajaj R G, Verma S. Direct ophthalmoscopy in very high degree of myopia. Indian J Ophthalmol [serial online] 1979 [cited 2022 Jan 19 ];27:35-36
Available from: https://www.ijo.in/text.asp?1979/27/3/35/31223
In very high degree of myopia, examination of fundus by a direct ophthalmoscope is very unsatisfactory. Duke Elder states that "if the degree of myopia is so great that the punctum remotum falls between the subject and the observing eye no image can be formed by any correcting lens on the observer retina." As a result the fundus examination in myopia above -25 to-30 D. can only be made by an Indirect ophthalmoscope. Unfortunately the Indirect ophthalmoscope is as yet not readily available in the clinics of an average practising ophthalmologist of our country. He depends on his familiar instrument, the "Direct ophthalmoscope." Keeping this in mind we have been trying to make use of the direct ophthalmoscope for this purpose.
Material and methods
It was observed that instead of trying to visualise the fundus by stronger and stronger concave lens in an attempt to neutralise the error of the subject, if we placed a convex lens of about +6 to+7 Dioptre, the fundus could be comfortably examined at a distance of about 8 inches from the subject. We kept on examining all such cases by both direct and indirect ophthalmoscope over a period of one year and were satisfied that this provides a satisfactory method of examining fundus of cases over-25 D. Though the illumination of image is inferior to that seen by indirect ophthalmoscope but the magnification is more and it provides an opportunity to examining these cases by direct ophthalmoscope.
In moderate emmetropes the retina of the subject can be seen clearly by an observer by placing a suitable corrective lens at the anterior focal point or even of the spectacle distance, since the emerging rays are rendered parallel by them. This is not possible in cases of very high myopia where the punctum remotum is inside the anterior focal point of the eye. In myopes of less degree but still of high order when the punctum remotum of the subject's eye falls between it and the observing eye, the observer can simply not accomodate for such a close range. In case the observer moves backwards with his ophthalmoscope (away from the subject) and sees this image, it is still not possible in as much as having formed the image, the rays diverge immediately, hence they cannot be caught by the observing eye beyond a very limited distance from their point of emergence, and this is quite close [Figure 1]. Thus an observer with a direct ophthalmoscope misses the image all the time. However, the true inverted areal image of the subject retina can be seen by the observer with the ophthalmoscope if the observer remains at a relatively close distance to the subject but augments his accomodation by using +6 or +7 convex lens in the ophthalmoscope aperture. The image can be seen clearly at a distance of 6 to 8 inches though it is not so bright as seen by an indirect ophthalmoscope. This method of direct ophthalmoscope is a very handy and useful method of examining the fundus of myopes over 25 D. which otherwise can only be seen by an indirect ophthalmoscope.
A new technique in examination of the fundii in cases of myopia over 25 D by a direct ophthalmoscope is envisaged. Direct ophthalmoscopy is done at a distance of about 6 to 8 inches with +6 D. to+8 D. lens in the ophthalmoscope aperture. The image thus seen is magnified inverted real image with less luminosity.
|1||Duke Elder Vol. 5 System of Ophthalmology Page 842-843. Henry Kimpton London.|