Indirect ophthalmoscopy

Monocular and binocular IDO

1. INDIRECT OPHTHALMOSCOPY SHAHANA NETHRADHAMA SCHOOL OF OPTOMETRY

2. INDIRECT OPHTHALMOSCOPY Examination of both the peripheral fundus and the posterior pole is possible with indirect ophthalmoscopy .

3. Indirect ophthalmoscopy should be used: When examining a patient with symptoms of shadows, hazy vision, flashes of light, and floaters, which may suggest retinal tear, detachment or other retinal abnormality. When following a patients with systemic diseases that have retinal manifestations, such as diabetes, high blood pressure, cardiovascular disease, sickle cell disease, infectious and autoimmune diseases. In patient with cataract or following cataract extraction. For older patients who are at greater risk of developing glaucoma and age related macular degeneration.

4. PRINCIPLE Indirect ophthalmoscopy(IDO)involves making the eye highly myopic by placing a high power convex lens (+13D to +30D) infront of the eye so that real, inverted and laterally reversed image is formed in front of lens The technique is called indirect because the fundus is seen through condensing lens.

5. Two method of indirect ophthalmoscopy: Monocular indirect ophthalmoscopy. Binocular indirect ophthalmoscopy.

6. MONOCULAR IDO Monocular IDO is handheld technique which produces real and erect image. It consist of: Illumination rheostat at its base Focusing lever for image refinement Filter dial with red free and yellow filters Forehead rest for steady proper observer head positioning. Iris diaphragm lever to adjust illumination beam diameter.

7. OPTICS An internal relay lens system re-invests, initially inverted image to real, which then magnified. This image is focusable using focusing lever.

8. ADVANTAGES: Increased working distance from patient Increased field of view at low magnification Erect, real imaging similar to direct ophthalmoscopy DISADVANTAGE: Limited illumination Fixed magnification No stereopsis INDICATION: Need for increased field of view, small pupil, uncooperative children, patients tolerance of bright light, basic fundus screening.

9. BINOCULAR IDO Viewing fundus by allowing stereoscopic examination. CHARACTERISTICS : Magnification of image depends upon the dioptric power of convex lens , position of the lens in relation of the eyeball and refractive state of eyeball. With a stronger lens image will be smaller but brighter and field of vision will be more.

10. PREREQUISITES Indirect ophthalmoscope Dark room Convex lens Pupil of the patient should be dilated.

11. TECHNIQUE: The patient’s pupil must be dilated. The procedure is explained to the patient and made to lie in supine position,instructed to keep both eye open. The examiner throw the light into the patient’s eye from an arm distance with BIO or that mounted on the spectacle frame. Keeping eyes on the reflex the examiner then interposes the condensing lens(various power ranging from +15D to +40D) in the path beam of light close to the patient’s eye and then slowly move the lens away from the eye until the image of retina is clearly seen.

12. The examiner moves around the head of the patient to examiner different quadrants of fundus. Examiner has to stand opposite to the clock hour position to be examined By asking the patient to look in extreme gaze and using scleral indenter, peripheral retina upto ora serrata can be examined.

13. Field of illumination More in myopia and less in hypermetropia as compared to emmetropia .

14. Image formation Emmetropia Myopia Hypermetropia

15. EMMETROPIA Emmetropic eye, rays from fundus are parallel, brought to a focus by the condensing lens. Image formed at the principal focus of lens. Hence, size of image remains the same, no matter the position of lens.

16. MYOPIA Rays are convergent Image formed in front of the eye Final image by condensing lens within its own focal length Image is smaller when lens is nearer to anterior focus of the eye and larger when away.

17. HYPERMETROPIA Rays are divergent and appear to come from behind the retina. Image by condensing lens in front of its principle focus Image is larger when lens is nearer to the anterior focus of the eye and smaller when away

18. Relative position of images In emmetropia: at the principal focus In myopia: nearer to the lens than its principal focus In hypermetropia: farther away from the principal focus

19. Factors affecting field of view Patient’s pupil size Power of condensing lens Refractive error Distance the condensing lens held from the patient’s eye

20. ADVANTAGES Wide range of view High contrast Stereoscopic view Variety of lens options Excellent depth of focus Lesser distortion image

21. DISADVANTAGES Inverted and inversed image Low magnification Dilation required Difficult to master

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