Methods of Subjective Refraction....pptx

Description of methods of subjective refraction

1. Methods of Subjective Refraction Dr. Fashola Maryam B.

2. Outline Introduction Refraction Subjective refraction Equipments Steps Considerations Methods

3. Introduction Refraction : The measurement of the eyes’ focusing characteristics and the determination of a patients need for correction. Objective : Patients input/cooperation is not required. Retinoscopy, Autorefractometry. Subjective : Requires patient input/cooperation. Subjective refraction : An attempt to determine, by trial and error, the combination of lenses that will provide the best corrected visual acuity, with the patients' contribution. Accuracy of the result depends largely on patients: Intelligence; Observational ability; Cooperation.

4. Equipment Phoropter: A complex lens holder designed to aid subjective refraction, allowing the examiner to change lenses efficiently and easily.

5. Equipment Visual acuity chart : Usually a Snellen chart, used to test visual acuity at 6metres OR at 3metres using a mirror and a reverse chart. Visual acuity is tested in a well-lighted room. Alternatives: logMAR chart, Landolt C, tumbling E chart, Jaeger chart, Lea test chart.

6. Equipment Trial lens box set: Trial lenses Trial frame Accessories: Plano lens Occluder Pinhole Near vision chart Red and green filter Prisms, etc.

7. Equipment Trial frame: A frame designed to permit insertion of different lenses used in refraction. It has knobs that allows for adjustment of IPD, nose bridge height, temple tilt and cylinder axis scale. It also comes with four compartments for several lens types while refracting. Types: Full aperture, Reduced aperture and Half-eye

8. Equipment Occluder : Opaque plastic disc used to close one eye while testing the other. Plano lens: has no power, can be used to check malingering.

9. Equipment Pinhole: It blocks peripheral rays of light allowing only the principal rays fall on the retina, thereby reducing the blur circle. V/A improves; vision can be improved with refraction. V/A stays the same or worsens; search for possible macular causes of poor vision or eccentric fixation.

10. Equipment Spherical lenses: come as pairs of plus and minus lenses, with same power in all meridians. Used to correct spherical errors. Cylindrical lenses: plus or minus cylinders, with power in one meridian and axis of cylinders marked on the rim of the lenses. Used to correct astigmatism.

11. Equipment Near vision chart: held at a distance of 33cms. Used to detect people with near vision difficulties (uncorrected hyperopia, presbyopia). Types: Roman test types; Snellen near vision chart; Jaeger chart.

12. Equipment Jackson Cross Cylinder (JCC) : A spherocylindrical lens in which the power of the cylinder is twice that of the sphere and of opposite signs. It is usually mounted on a handle which is 45 to the axis of the cylinder and is used for astigmatic refinement. The commonly used cross cylinders are +/-0.25 and +/-0.50.

13. Equipment Alternatives: Astigmatic fan chart, Astigmatic clock dial. Stenopaeic slit: Opaque disc with a 1mm wide and 15mm long slit aperture in its centre. It allows rays of light pass through only one meridian and thus can be used to determine astigmatic axis.

14. Equipment Duochrome chart: Used to verify the final refraction and to prevent over- or under-correction. It is based on the principle of chromatic aberration i.e. shorter wavelengths of light (i.e., green) is refracted more by the eye than longer wavelengths of light (i.e., red). In emmetropes, yellow light (570mm) is focused on the retina, green light (535mm) is focused in front of the retina (1.50D) and red light (620mm) is focused behind the retina (0.50D). Can be used in colour blind as it’s not based on colour discrimination.

15. METHODS History: Patients age, occupation and hobbies; Blurred vision for near or far; Eye ache, eye fatigue, frontal headache; Jumping lines while reading; Previous eye exam; Intervention e.g. Spectacle use; History of systemic illnesses (Hypertension, diabetes etc); Family history of cataract, glaucoma or blindness.

16. METHODS General examination: To rule out systemic illness(es). Visual acuity Uncorrected visual acuity: to know the current refractive status of the eye. Visual acuity with correction: gives information as to the possibilities for improvement. Visual acuity with pinhole: helps establish if vision may be improved with refraction. Near visual acuity: tested at 33 – 40cm.

17. METHODS Ocular examination: Lid : Ptosis, Large or multiple chalazia inducing astigmatism. Globe : Strabismus, Large globe suggesting myopia. Conjunctiva : Pterygium inducing astigmatism. Cornea : Keratoconus, Corneal oedema. Anterior chamber : Shallow in hyperopes. Pupil : RAPD, miosis, mydriasis. Lens : Cataract, Aphakia, Pseudophakia. Fundus : Small disc in hyperopes, large disc in myopes, oval disc in astigmats ; could reveal other pathologies.

18. METHODS Determine starting point of refraction Results of retinoscopy Results of autorefractometry Results from focimetry: to check previous prescription. This can also be done by neutralization in the absence of a focimeter. From scratch (estimating from patients V/A).

19. Refraction estimation from V/A 6/9: 0.50DS 1.00DC 6/12: 1.00DS 2.00DC 6/18: 1.50DS 3.00DC 6/24 to 6/36: 2.00DS 4.00DC 6/60: 3.00DS 5.00DC

20. METHODS Note: Test is done under good illumination, with minimal shadows around chart. Adjust temple behind patients ear and ensure frame sits comfortably on nose bridge. Adjust IPD so trial frame is straight, and eye aligns with lens centre. Ensure patient is comfortably seated. Occlude fellow eye while testing the other. Put next lens in trial frame before taking out previous one. Endpoint: combination of lenses that provides the best visual acuity with accommodation relaxed.

21. STEPS Refine the sphere Duochrome test Refine cylinder axis Refine cylinder power with sphere compensation Refine best sphere Binocular balancing Near vision

22. MEDTHODS: Refine sphere With the sphere from the starting point in place, and fellow eye occluded Check the best visual acuity with this as starting point. Take a +0.25D and -0.25D, show patient the two lens options, asking which makes their visual acuity clearer, add that which makes patient read more letters. Keep repeating until the patient reports no further improvement in visual acuity. NOTE: with minus lenses, patient has to earn an additional minus, i.e. patient must read more letters with an additional minus lens.

23. Duochrome test This is done to verify the sphere correction Green clearer (under-corrected for hyperopia or over-corrected for myopia), add +0.25DS; Red clearer (under-corrected for myopia or over-corrected for hyperopia), add -0.25DS. NOTE: Loose red/green lens filters can be used in the absence of a chart.

24. METHODS: Refine Cylinder axis Ask patient to look at a line one step larger than current V/A, with the objective cylinder in place Hold the JCC with its handle straddling the axis of the objective cylinder. Flip the JCC in position 1 and 2, asking the patient in what position object appears clearer/sharper (Always better to use a letter like O or D). Rotate the axis of the cylinder 5 or 10 clockwisely or anti-clockwisely in the direction of the red mark on the JCC. Repeat this step, and keep rotating until patient reports both views as equally sharp/dark. NOTE : If patient’s preference was in the direction of last axis, rotate back by half the amount rotated the last time.

25. Refine Cylinder power Align the red /power dots on the JCC with axis of the cylinder in trial frame. Flip the JCC such that both power options are made available to the patient, and ask which is preferable. If patient responds that both views are the same, cylinder power in frame is correct. If patient prefers the red(minus) dots, add -0.25DC, and continue until patient responds to both views being the same. Note: For every -0.50DC added to the trial lens, maintain spherical equivalent by changing the sphere half as much in the opposite direction i.e., add +0.25DS to the initial sphere.

26. Refine cylinder power If patient prefers the white/positive view, remove -0.25DC, repeat until patient finds no difference between the two views. Note: For every -0.50DC removed from the trial lens cylinder, maintain spherical equivalent by changing the sphere half as much in the opposite direction i.e., remove +0.25DS from the initial sphere. Note: If you have to change your power by more than -0.75DC, recheck the axis or recheck the objective refraction.

27. Binocular balancing To ensure both eyes not accommodating, Have both eyes open. Add +1.00 D over the eye not being tested (left) & Check visual acuity is decreased to 6/12 or by about 4lines from their BCVA. Compare +0.25 to -0.25 over the eye being tested (right); ask the patient which lens is clearer. If one lens is clearer adjust the sphere in that direction. Repeat the comparison until equal. Repeat step for other eye. Repeat step for other eye. Alternatively, repeat Duochrome test.

28. Near vision Check near visual acuity with best correction in place, at patient’s regular reading distance. Add +0.25DS to bring patient’s reading distance closer. Add -0.25DS to take reading distance farther.

29. References Clinical optics by A.R. Elkington, H.J. Frank, and M.J. Greaney. A Basic guide to practical refraction for new residents in ophthalmology by Chimdi M. Chuka- Okosa . Cybersight online resources.