Direct distant ophthalmoscopy is done from a distance of:
Correct Answer: 25 cm
Description: B i.e. 25 cm Distant direct opthalmoscopy is performed using a plane mirror or an opthalmoscope with a plane zero powered lens in position from a distance of 22 cm (20-28 cm) Q Applications of distant-direct-opthalmoscopy The diagnose opacity in the refractory media, which is seen as black reflex - The whole field may be black when the lens is entirely opaque or when there is blood in vitreous - A floating opacity (which becomes motile on eye movement & continue to move even after the eye is brought to rest) must be either in aqueous or vitreous If the eye is moved slightly in given direction, opacities in the pupillary plane (2) will appear stationary. Those in front of that plane (1) will move in the same direction, and those behind, (3, 4, 5) will appear to move in the opposite direction. If 4 is the centre of rotation of the eye and the eye is rotated slightly, all the opacities except 4 will move, the movement being greater when the opacity is faher from the centre of rotation. The centre of curvature of cornea is situated 8 mm behind its anterior surface (less than 1 mm behind 3 in fig). The corneal reflex the image of the mirror formed by cornea is a viual image situated 4 mm behind the anterior corneal surface that is a sho distance behind the anterior surface of the lens (behind 2 in fig). The corneal reflex will always cover the centre of curvature of cornea, no matter what the position of eye. Hence an opacity situated here will always be covered by the corneal reflex. Opacities in front of the corneal reflex move in the same direction with regard to reflex, and opacities behind it move in the opposite direction to the movement of the eye. To differentiate between a mole & a hole of the iris, as the mole looks black but a red reflex is seen through the hole in the iris. To recognize detached retina or a tumor arising from fundus as indicated by grayish reflex.
Category:
Ophthalmology
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