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Errors 2
The document discusses assessment and correction of refractive errors. It provides information on objective refractive assessment tools like retinoscopy and autorefraction. It also discusses subjective refraction techniques and considerations for different patient types. Key points include using cycloplegic refraction for infants and uncooperative patients, adjusting IPD with the phoropter, and transposing cylinders to determine the spherical equivalent.
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Errors 2
- 1. The two PrincipalMeridians (of highest & lowest power) are NOT at right angle to each others, and change of power from one meridian to the other is NEITHER gradual NOR regular • Corneal scars • KCN
- 2. • Accommodative asthenopia;continuous attempts of the ciliary muscle to compensate the error • Blurred vision; near & far • Running letters • Distorted objects
- 3. • Cornea: scars,stitches, … • Lens: subluxation • Retina: Staphyloma • e.g. Oil droplet in KCN (Charleux) • Oval optic disc (different refraction along the two principal meridians) • Tilted optic disc (Retinal astigmatism)
- 4. • Scissoring reflexin KCN • Different dioptric power in the two principal meridians • Measure Objectively the refractive error of the eye • Measures the corneal curvature & dioptric power
- 5. • Irregular cornealcircles • Pseudo-colour mapping of corneal curvature, power & thickness
- 6. • The patientsees the line in one meridian sharper than that on the perpendicular meridian
- 7. Cylindrical Lenses With itsaxis perpendicular to the ocular axis to be corrected
- 8. Sphero-Cylindrical Lenses The sphericallens renders the error as simple astigmatism The cylindrical lens corrects the residual astigmatic error
- 9. For low astigmaticerrors In KCN
- 10. • A cornealflap is fashioned by an automated keratome • Excimer laser is used to ablate the steep corneal meridian • The flap is re-positioned
- 11. • Partial thicknesscorneal incisions at the steeper corneal meridian • Applied in low astigmatic errors
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- 13. A mark onthe IOL denotes the axis of astigmatism to be corrected
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- 15. • Physiological recessionof near point of accommodation • Increased lens stiffness • Weak ciliary muscle
- 16. • Usually startsaround the age of 40 years (earlier in hyperopes) • Poor near vision e.g reading, sewing • Good far vision • Accommodative asthenopia
- 17. • Monfocal: Reading glassesseparate from distant glasses Convex Lens
- 18. • Bifocal glasses •Progressive Addition Lenses (PALs)
- 19. • 1st Correctvision for FAR • Measure the Near Point of Accommodation (PP) • Calculate Amplitude of Accommodation; (1 / PP) • Keep 1/3 accommodation as reserve to give the presbyope range for reading • Correct only the remaining 2/3 • Measure the working distance (usually 33 cm) • Calculate lens power needed to focus at the working distance (1/0.33 = 3D) • Determine the power of the lens needed for correction of Presbyopia (Power at working distance - Power at PP) • Add this power to the power needed for far correction RAF Rule
- 20. • A 45year old presbyope with + 2D for far • PP at 40 cm • Amplitude of Accommodation = 1/0.40 = 2.5D • 1/3 is kept as reserve i.e 1/3 2.5 = 0.75 D) • Correct only the remaining 2/3 (2.5 - 0.75 = 1.75 D) • Measure the working distance (usually 33 cm) • Calculate lens power needed to focus at the working distance (1/0.33 = 3D) • Determine the power of the lens needed for correction of Presbyopia (3 - 1.75 = 1.25 D)) • Add this power to the power needed for far correction (1.25 + 2 = 3.25 D)
- 22. Convex Lens • Bifocallenses
- 23. • Excimer laseris used to changes the shape of the cornea to create different power zones for seeing at varying distances
- 24. • Partial thicknessscleral pockets are made in each of the 4 eye quadrants • PMMA (PolyMethyl MethaAcrylate) bands are injected into theses pockets • The aim is to expand the scleral ring at the zone of ciliary body, thus stretching the zonules
- 26. • Absence ofthe crystalline lens • Rare • Trauma • Post operative
- 27. • Defective farvision; because of hypermetropia • Defective near vision; due to loss of accommodation • History of surgery or trauma
- 28. • Scar ofcataract extraction surgery • Scar of ruptured globe • Only two Purkinje Sanson images absence of the two Purkinje Sanson images formed by anterior & posterior surfaces of the lens
- 29.
- 30. • Tremulous (Loss of supportby the lens), Iridodonesis
- 31. • Jet black colour (Normally agreyish hue appears in phakic clear lenses)
- 32. • High hypermetropia(+ 10 D or more) • Astigmatism Against the rule (Because of contraction of the corneal scar at 12 o’clock position, causing flattening of the vertical meridian) • Anisometropia (In unilateral aphakia)
- 33. Convex Lenses In Bilateral aphakia Prescribeseparate glasses for distant & near correction or use bifocals or PALs Convex Lenses In Bilateral or Unilateral aphakia Prescribe Bifocal Lenses, or Monofocal lenses with reading glasses
- 34. It is thebest option (Least image magnification) Might be used in Unilateral or Bilateral aphakia Implant monofocal IOLs with additional reading glasses, or implant multifocal IOL
- 35. • Reading ADDin aphakic eyes is + 3D (Accommodation is lost) • Disadvantages of Glasses in correction of Aphakia: 1. Image magnification (30%); Anisometropia in unilateral cases 2. Peripheral abberation 3. Visual field constriction 4. Thick heavy lenses with poor cosmoses
- 36. • A differenceof refractive power between the two eyes of 4 D or more • Common • Aphakia
- 37. Anis-eiokonia Different image size in botheyes (>30%)
- 38.
- 39. • Causes lesschange in image size (10%) • LASIK • IOL Implantation (1% change in image size)
- 40. • Objective methodfor assessment of refractive state of the eye by: Illuminating the eye Observation of the direction of movement of red reflex
- 41.
- 42. • Put CycloplegicE.D • Back of the eye is illuminated with a streak light coming out of the retinoscope • The Examiner moves the retinoscope from side to side & up and down, observing the red reflex • WITH movement indicates Hyperopia (Put plus lenses) • AGAINST movements indicates Myopia (Put minus lenses) • NO movement indicates emmetropia (Neutral Point) • Subtract Working distance at the end
- 43. + 0.5 DS, +2.00 DC, Axis 180 + 1.5 DS, - 5.00 DC, Axis 90 - 3.5 DS, + 5.00 DC, Axis 180
- 44. • Automated, Objectivemethod for assessment of refractive state of the eye • Myopia: Prescribe the lowest minus lens that gives the best VA • Hyperopia: Prescribe the highest plus lens that gives the best VA • Astigmatism: High cylinder lenses causes image distortion • Reading Correction is added to the spherical component only
- 45. • Automated, Objectivemethod for assessment of refractive power, Curvature & thickness of the cornea
- 46. ASSESSME NT OF REFRACTIV E ERRORSMOHAMEDABDELZAHER MD, FRCS
- 48. Diminution of vision Defective night vision Difficultnear vision Headache Running letters Frowning to see better Ocular Deviation
- 49.
- 50. History Systemic Diseases Drugs The prescription ofspectacles should be delayed until a stable refraction is obtained, if possible. Chronic hyperglycaemia myopia Chronic hypoglycemia hyperopia Acute changes in plasma glucose level hyperopia Fukimi O et al Refractive changes in diabetic patients during intensive glycemic control. Br J Ophthalmol 2000;84:1097–1102.
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- 54. WHY IS THEPATIENT COMPLAINING?!! 😏 To Declare that the patient is seeing a line, he must read at least ½ of the line correctly.
- 55. More evident inAmblyopia
- 56. Pin Hole Vision improves VisionworsensNo changeRefractive error Corneal opacity Cataract Vitreous hemorrhage Macular lesion
- 57.
- 58. • Objective methodfor assessment of refractive state of the eye by: Illuminating the eye Observation of the direction of movement of red reflex
- 59. • Automated, Objectivemethod for assessment of refractive state of the eye • Myopia: Prescribe the lowest minus lens that gives the best VA • Hyperopia: Prescribe the highest plus lens that gives the best VA • Astigmatism: High cylinder lenses causes image distortion • Reading Correction is added to the spherical component only View through an autorefractor
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- 63. Transposition + 0.50 DS,- 0.50 DC / 85 0.00 DS, + 0.50 DC / 175 Equals
- 64.
- 65. If you arenot willing to learn, No one can help you. If you are willing to learn, No one can stop you.