Direct ophthalmoscope

For Ophthalmology trainees

1. Direct Ophthalmoscope Dr. R S Walpitagamage Registrar in Ophthalmology Colombo North Teaching Hospital,Ragama Sri Lanka

2. “A physician using a direct ophthalmoscope is like, one-eyed Eskimo peeping in to an igloo from the entry way with a flash light”

3. History.. Charles Babbage 1847 Hermann von Helmholtz 1851

4. Introduction The direct ophthalmoscope is commonly used for routine examination of the fundus of the eye, especially when a slit lamp cannot be used. It is small Easily portable Can also be used to examine the more anterior parts of the eye

5. The instrument consists of a system of lenses which focus light from an electric bulb on to a mirror where a real image of the bulb filament is formed. The mirror reflects the emitted light in a diverging beam which is used to illuminate the patient's eye. Reflected rays from patients retina refracted by patients crystalline lens become parallel and enters into the observed eye through the mirror hole and the observer views the illuminated eye. The image of the bulb is formed just below the hole so that its corneal reflection does not lie in the visual axis of the observer. Optics of Direct Ophthalmoscope

6. Patient’s eye Observer’s eye Mirror with a hole Light source Aperture Lens Optics of Direct Ophthalmoscope Compensation lens

7. Detailed structure of direct ophthalmoscope showing the illumination and viewing optical system

8. Direct Ophthalmoscope Patient side Front surface mirror Crossed Linear Polarizing filter/red free Filter switch Our side Rubber brow rest Lens selection disc Illuminated lens indicator On/Off switch Aperture Selection dial

9. APERTURES AND FILTERS Small Aperture : Provides easy view of the fundus through an undilated pupil. Always start the examination with this aperture and proceed to micro aperture if pupil is particularly small and/or sensitive to light. Large Aperture : Standard aperture for dilated pupil and general examination of the eye. Micro Spot Aperture : Allows easy entry into very small, undilated pupils. Slit Aperture : Helpful in determining various elevations of lesions, particularly tumors and edematous discs.

10. APERTURES AND FILTERS Fixation Aperture : The pattern of an open center and thin lines permits easy observation of eccentric fixation without masking the macula. Cobalt Blue Filter : Blue filter used with fluorescein dye permits easy viewing of small lesions, abrasions, and foreign objects. Red-Free Filter : Excludes red rays from examination field for easy identification of veins, arteries, and nerve fibers.

11. Specifications

12. How to Conduct an Ophthalmologic Examination with a Direct Ophthalmoscope In order to conduct a successful examination of the fundus, the examining room should be either semi darkened or completely darkened. It is preferable to dilate the pupil when there is no pathologic contraindication, but much information can be obtained through the undilated pupil. The following steps will help the practitioner obtain satisfactory results: 1. For examination of the right eye, sit or stand at the patient’s right side. 2. Select “0” on the illuminated lens disc of the ophthalmoscope and start with the small aperture.

13. 3. Take the ophthalmoscope in the right hand and hold it vertically in front of your own right eye with the light beam directed toward the patient and place your right index finger on the edge of the lens dial so that you will be able to change lenses easily if necessary. 4. Dim room lights. Instruct the patient to look straight ahead at a distant object. 5. Position the ophthalmoscope about 6 inches (15 cm) in front and slightly to the right (25º) of the patient and direct the light beam into the pupil. A red “reflex” should appear as you look through the pupil.

14. 6. Rest your left hand on the patient’s forehead and hold the upper lid of the eye near the eyelashes with the thumb. While the patient is fixating on the specified object, keep the “reflex” in view and slowly move toward the patient. The optic disc should come into view when you are about 1 to 2 inches (3-5 cm) from the patient. If it is not focused clearly, rotate lenses with your index finger until the optic disc is as clearly visible as possible. The hyperopic, or far-sighted, eye requires more “plus”(green numbers) lenses for clear focus of the fundus; the myopic, or nearsighted,eye requires “minus” (red numbers) lenses for clear focus.

15. 7. Now examine the disc for clarity of outline, color, elevation and condition of the vessels. Follow each vessel as far to the periphery as you can. To locate the macula, focus on the disc, then move the light approximately 2 disc diameters temporally. You may also have the patient look at the light of the ophthalmoscope, which will automatically place the macula in full view. Look for abnormalities in the macula area. The red-free filter facilitates viewing of the center of the macula.

16. 8. To examine the extreme periphery, instruct the patient to: • Look up for examination of the superior retina • Look down for examination of the inferior retina • Look temporally for examination of the temporal retina • Look nasally for examination of the nasal retina. This routine will reveal almost any abnormality that occurs in the fundus. 9. To examine the left eye, repeat the procedure outlined above but hold the ophthalmoscope in your left hand, stand at the patient’s left side and use your left eye.

17. USE OF FIXATION TARGET Direct the patient to focus on the center of the fixation target projected within the light beam. Simultaneously check the location of the pattern on the fundus. If the center of the pattern does not coincide with the macula, eccentric fixation is indicated. In this procedure, the crossed linear polarizing filter is especially useful since it dramatically reduces reflections caused by the direct corneal light path.

18. ADDITIONAL EXAMS WITH COAXIAL OPHTHALMOSCOPE By selecting the +15 lens in the scope and looking at the pupil as in a fundus examination [2 inches (5 cm) distance from the patient], the examiner may verify doubtful pupillary action. One can also easily detect lens opacities by looking at the pupil through the +6 lens setting at a distance of 6 inches (15 cm) from the patient. In the same manner, vitreous opacities can be detected by having the patient look up and down, to the right and to the left. Any vitreous opacities will be seen moving across the pupillary area as the eye changes position or comes back to the primary position.

19. Field of view The area of retina which can be seen at any one time is called the field of view. It is governed by the projected image of the sight-hole on the retina , the hole in the mirror or the observer's pupil, whichever is the smaller. Smaller than the field of illumination. Direct ophthalmoscope. Image of sight-hole formed by emmetropic eye. R = retina; P = principal plane. The image A1 B1 of the sight-hole AB is constructed using a ray through the nodal point-N, and a ray parallel to the visual axis which is refracted by the eye to pass through its posterior focal point.

20. Factors affecting field of view in Direct Ophthalmoscopy Axial length of observed eye The figure shows the field of view (a-b) is smaller in a myopic eye-Rm larger in a hypermetropic eye-Rh than in an emmetropic eye-R.

21. Factors affecting field of view in Direct Ophthalmoscopy 2. Size of the pupil of observed eye This figure shows the effect of pupil size on field of view -a b The field of view is considerably enlarged when the pupil is dilated; hence the advantage of instilling a mydriatic prior to fundoscopy . Small pupil- ab smaller Large pupil – ab larger

22. Factors affecting field of view in Direct Ophthalmoscopy 3. Distance between the observed eye and the observer In order to utilize the maximum available field of view it is necessary for the observer to be as close as possible to the patient's eye. Figure shows that as the distance between the patient and the observer decreases, the field of view –a b (the projected image of the sight-hole on the patient's retina) becomes larger.

23. Light reflected from the illuminated retina of the patient's eye passes back, through the hole in the mirror and into the observer's eye. The position and size of the image formed in the observer's eye can be constructed by first constructing the image, xy , of the illuminated retina XY which is formed at the patient's far point. A ray from the top of that image, passing through the observer's nodal point-N o , locates the position of the top of the image- X'Y', on the observer's retina -R o . R-the patient's retina, P- principal plane, N- nodal point Fa -anterior focal point respectively R o , P o and N o refer to the observer’s retina, principal plane and nodal point.

24. An emmetropic observer viewing an emmetropic patient The rays of light leaving the patient's eye are parallel and are therefore focused on the observer's retina without any accommodative effort or the use of a correcting lens. Patient’s eye acts as a simple magnifier 60D/4=15D

25. An emmetropic observer viewing a hyperopic patient If the patient is hypermetropic , a diverging beam of light leaves his eye and it behaves an emmetropic observer to accommodate or to use a correcting convex(plus) lens in order to bring the light to a focus on his retina.

26. Patient’s eye Observer’s eye Mirror with a hole Light source Aperture Lens Convex lens An emmetropic observer viewing a hyperopic patient Divergent rays

27. An emmetropic observer viewing a hyperopic patient- with correcting convex lens The retina of a hyperopic eye will be magnified less than 15x because of the reverse Galilean telescope created by the optics of the eye and the lens of the direct ophthalmoscope The image formed on the observer's retina is smaller when a hypermetropic eye is viewed Field of view is wider in hypermetropia. Thus, when examining very hypermetropic eyes a small image of a wide field of view is seen and the whole fundus can be scanned quickly.

28. An emmetropic observer viewing a myopic patient An emmetropic observer viewing a myopic eye receives a converging beam of light which is brought to a focus in front of his retina. X’ is a blur circle and the observer sees a blurred image unless he uses a correcting concave(minus) lens.

29. Patient’s eye Observer’s eye Mirror with a hole Light source Aperture Lens Concave lens An emmetropic observer viewing a myopic patient Convergent rays

30. An emmetropic observer viewing a myopic patient- with correcting concave lens If the subject eye is myopic, the extra plus power of the eye's optics and the minus power dialed into place in the ophthalmoscope together form a Galilean telescope, increasing magnification and decreasing the field of view. The enlargement of image size seen when a myopic eye is examined, coupled with the reduced field of view as compared with an emmetropic eye results in the observer seeing a magnified but restricted view of the myopic fundus. Also, in axial myopia the eye itself is bigger than an emmetropic eye. Thus it is difficult to examine a myopic fundus using the direct ophthalmoscope because the field of view is so small compared with the size of the fundus.

31. If the subject is having an astigmatism.. It is impossible to secure a perfect view of the fundus of an astigmatic eye because the only correcting lenses in the ophthalmoscope are spherical. It is thus only possible to correct one meridian at a time. If the degree of astigmatism is high, the difference in image size due to the disparity of dioptric power of the eye in the two principal meridians causes distortion of the image and the optic disc appears oval.

32. If the observer has a refractive error.. Two possibilities, The observer can remove his spectacles and rack up the appropriate lens in the ophthalmoscope to give a clear view of the patient's fundus. The appropriate lens is the algebraic sum of his own and the patient’s refractive error The observer can use the instrument with his glasses on. However, his field of view will be restricted as the sight-hole in the mirror will be further from his eye.

33. Direct ophthalmoscopy in summary… Observer Patient Myopic Hyperopic Emmetropic Emmetropic Myopic Hyperopic Astigmatism Astigmatism Use minus lens Larger image Small field of view Difficult to examine Use plus lens Smaller image Larger field of view Easy to examine Difficult to correct Image distortion 1.Use spectacles with reduce field of view 2.Remove spectacles Add relevant lens power

34. Past questions(MD Ophthalmology module-3) 2017 April & 2005 July - Compare and contrast the optical principles of Indirect Ophthalmoscope and Direct Ophthalmoscope using Ray Diagrams. (70%) 1990 Nov- Describe optical principal of direct and indirect ophthalmoscopy with diagrams and discuss their clinical advantages.

35. Direct Ophthalmoscopy Advantages over Indirect Relatively easy to perform and no need of well trained person to examine and interpret Higher magnification 15 times(5 in indirect) Possible to examine through undilated pupil Less discomfort to the patient No need of supine position Less intense light No indentation Disadvantages over indirect No 3D view(stereopsis) Uniocular examination Relatively difficulty to examine with eye movements Difficult to perform in babies-ROP Impossible to perform procedures like indirect laser Difficult to examine patients with high spherical/astigmatism More image distortion Relatively small area of retina can be examined 50-70% Difficult to see the peripheries as no indentation is used

36. References

37. Thank You!