06 refractive error

These lectures has prepared for postgraduate student (Ophthalmology) according to the curriculum of Bangladesh College of Physician and Surgeons (BCPS) and Bangabondhu Sheikh Mujib Medical University (BSMMU) Bangladesh

1. Refractive error Prof Md Anisur Rahman Head of the Department (Ophthalmology). Dhaka Medical College. Dhaka 9 Sept 2019 (LIONS) 1 [email protected]

2. Important topics of refractive error Hypermetropia Definition Types 9 Sept 2019 (LIONS) [email protected] 2

3. Myopia Definition Treatment Types Diff between simple & pathological myopia Treatment Other myopia 9 Sept 2019 (LIONS) [email protected] 3

4. Astigmatism Definition Symptoms Treatment Different types of astigmatism 9 Sept 2019 (LIONS) [email protected] 4

5. Emmetropia Emmetropia: (Optically normal eye, no refractive error is at their) is defined as a state of refraction, when the parallel rays of light coming from infinity are focused at retina, when accommodation is at rest. 9 Sept 2019 (LIONS) 5 [email protected]

6. Ametropia Ametropia: (Optically non normal eye, refractive error is at their) is defined as a state of refraction, when the parallel rays of light coming from infinity are focused either in front or behind the retina, when accommodation is at rest. 9 Sept 2019 (LIONS) 6 [email protected]

7. Types of ametropia There are three types of ametropia: Hypermetropia Myopia and Astigmatism 9 Sept 2019 (LIONS) 7 [email protected]

8. Hypermetropia 9 Sept 2019 (LIONS) 8 [email protected]

9. What is Hypermetropia (long sightedness)? When parallel rays of light from infinity comes to a focus behind the retina when accommodation is at rest. 9 Sept 2019 (LIONS) 9 [email protected]

10. Why it is called long sightedness? The alternative name of for hypermetropia, long sightedness , is quite acceptable except in so far as it has given rise to confusion in the layman’s mind. A patient will often describe himself as very long sightedness when what he intends to convey is that he sees well in the distance and presumes himself to be optically normal; it is, of course, true that early in life the hypermetrope sees as well in the distance as the emmetrope . 9 Sept 2019 (LIONS) 10 DUKE ELDER 45

11. Some facts about hypermetropia It is the commonest refractive error At birth practically all eyes are hypermetropic to the extent of 2.5 to 3.0 Diopter When adolescence is passed, the eye should theoretically be emmetropic But about 50% doesn’t reached there and some degree of hypermetropia is persists Some may be overshoot and become myopic 9 Sept 2019 (LIONS) Duke-Elders: 45 11

12. Etiological classification of Hypermetropia Axial: This is the commonest of all types of ametropia. One mm shortening of eyeball causes 3 D of hypermetropia. 9 Sept 2019 (LIONS) 12 [email protected]

13. Etiological classification of Hypermetropia 2) Index: This type of hypermetropia may occur physiologically in old age due to decrease in the refractivity of the lens or pathologically in DM under treatment when blood sugar level falls or in cortical cataract. The outstand example of index hypermetropia is APHAKIA. 9 Sept 2019 (LIONS) 13 [email protected]

14. Etiological classification of Hypermetropia 3) Curvature: This type of hypermetropia occurs due to decrease in the curvature of any refracting surface. Usual site of defect is in the cornea. 1 mm changes in the radius of curvature of cornea causes 6 D of hypermetropia. 9 Sept 2019 (LIONS) 14 [email protected]

15. Nomenclature of Hypermetropia (components of hypermetropia) Total Hypermetropia: Is the total amount of refractive error, which is estimated after complete cycloplegia with atropine. It consists of Manifest and Latent Hypermetropia. 9 Sept 2019 (LIONS) 15 [email protected]

16. Nomenclature of Hypermetropia (components of hypermetropia) Latent Hypermetropia Which is counteracted by the tone of the ciliary muscle and can only be disclosed by abolition of the tone of the ciliary muscle the latent hypermetropia is disclosed when refraction is carried after abolishing the tone with atropine. 9 Sept 2019 (LIONS) 16 [email protected]

17. Nomenclature of Hypermetropia (components of hypermetropia) Manifest Hypermetropia Is that portion of hypermetropia which in normal condition remains uncorrected, and not corrected by ciliary tone. It consists of two components Facultative and Absolute hypermetropia 9 Sept 2019 (LIONS) 17 [email protected]

18. Nomenclature of Hypermetropia (components of hypermetropia) Facultative & Absolute hypermetropia Facultative hypermetropia: Which can be corrected by accommodation Absolute hypermetropia: Which can’t be corrected by accommodation 9 Sept 2019 (LIONS) 18 [email protected]

19. Nomenclature of Hypermetropia (components of hypermetropia) Latent Hypermetropia Total hypermetropia Manifest Hypermetropia   Facultative Absolute 9 Sept 2019 (LIONS) 19 [email protected]

20. Suppose a patient can read 6/9 without any aid. Now, if with +1.00 D sphere he can just read 6/6, this is his absolute hypermetropia . Now, if with addition of another +0.50 D sphere he can still read 6/6 this is his facultative hypermetropia . These two combined together (+1.00+0.50) the manifest hypermetropia. 9 Sept 2019 (LIONS) 20 [email protected]

21. If this patient after full atropinization can read with another addition of +1.00 D shpere, 6/6 is his latent hypermetropia. Then the total hypermetropia (Absolute + F acultative + Latent ) = (1 + 0.5 + 1.0 = 2.5 ) of this patient is +2.50 Dsh. 9 Sept 2019 (LIONS) 21 [email protected]

22. OSPE: 1 Your patient needs +2.00 D to see distance clearly. However, he can tolerate up to +4.00D without getting blurred distance vision. His cycloplegic refraction is +6.00D sphere. What are the values in diopter of his? 9 Sept 2019 (LIONS) 22 [email protected]

23. Absolute hypermetropia? Manifest hypermetropia? Facultative hypermetropia? Latent hypermetropia? 9 Sept 2019 (LIONS) 23 [email protected]

24. 1) Absolute Hypermetropia:+ 2.00 D It is the minimum power which causes vision 6/6 9 Sept 2019 (LIONS) [email protected] 24

25. 2) Manifest hypermetropia = + 4.00D ( M anifest hypermetropia is defined as without cylcoplegia, the most plus correction that can be tolerated without blurring of vision) 9 Sept 2019 (LIONS) 25 [email protected]

26. 3) Facultative hypermetropia = + 2.00D (Facultative hypermetropia is defined as the difference between absolute and manifest hypermetropia + 4.00D - + 2.00D = + 2.00 D) 9 Sept 2019 (LIONS) 26 [email protected]

27. 4) Latent hypermetropia = + 2.00 D     (latent hypermetropia is defined as the difference between manifest hypermetropia and hypermetropia measured with cycloplegia + 6.00D - + 4.00D = + 2.00D) 9 Sept 2019 (LIONS) 27 [email protected]

28. Symptoms of Hypermetropia: In patient with hypermetropia, the symptoms vary depending upon the age of the patient and the degree of refractive error. These can be grouped as under: 9 Sept 2019 (LIONS) 28 [email protected]

29. 1) Asymptomatic: A small amount of refractive error in young patients is usually corrected by mild accommodative effort without producing any symptoms 9 Sept 2019 (LIONS) 29 [email protected]

30. 2) Asthenopic symptoms: At times the hypermetropia is fully corrected (thus vision is normal) but due to sustained accommodative efforts patient develops asthenopic symptoms. These include: Tiredness of the eyes, Frontal and frontotemporal headache, Watering and Mild photophobia 9 Sept 2019 (LIONS) 30 [email protected]

31. 3) Defective vision with asthenopic symptoms: When the amount of hypermetropia is such that it is not fully corrected by the voluntary accommodative efforts, then the patient complains of defective vision more for near than distance associated with asthenopic symptoms due to sustained accommodative efforts. 9 Sept 2019 (LIONS) 31 [email protected]

32. 4) Defective vision only: When the amount of hypermetropia is high (more than 4D), the patients usually do not accommodate (especially adults) and there occurs marked defective vision for near and distance. 9 Sept 2019 (LIONS) 32 [email protected]

33. 5) Crossed-eye sensation: Some patients may feel that their eyes are crossing without any diplopia. It also occurs due to excessive accommodation 9 Sept 2019 (LIONS) 33 [email protected]

34. Factors to be consider prescribing spectacle Age of patient: Younger patient have more accommodative power, so under correct. Symptom: No symptom, no treatment. Accommodative state of the patient: If the Latent Hypermetropia is more, under correct. Muscle balance: In case of esophoria or esotropia full correction is indicated to relieve extra accommodation. Consideration of general health Profession. 9 Sept 2019 (LIONS) 34 [email protected]

35. Treatment: 1) Optical treatment Basic principal of treatment is to prescribe convex (plus) lenses, so that the light rays are brought to focus on the retina Fundamental rules for prescribing glasses in hypermetropia include: Total amount of hypermetropia should always be discovered by performing refraction under complete cycloplegia 9 Sept 2019 (LIONS) 35 [email protected]

36. If the total manifest refractive error is small, e,g, 1 D or less, correction is given only if the patient is symptomatic The spherical correction given should be comfortable to the patient. However, the astigmatism should be fully corrected. Gradually increase the spherical correction at 6 months interval till the patient accepts manifest hypermetropia 9 Sept 2019 (LIONS) 36 [email protected]

37. If there is associated exophoria, the hyperopia should be under corrected by 1 to 2 D In the presence of accommodative convergent squint, full correction should be given at the first sitting If there is associated amblyopia, full correction with occlusion therapy should be started. 9 Sept 2019 (LIONS) 37 [email protected]

38. It is important to remember that in children hypermetropia may diminish with the growth of the child. So, refraction should be carried out every six months and if necessary the correction should be reduced. 9 Sept 2019 (LIONS) 38 [email protected]

39. Treatment: 2 Contact lenses Contact lens is the another option. When there is high hypermetropia, the glass becomes thick & heavy weight, in this case contact lens is another option 9 Sept 2019 (LIONS) 39 [email protected]

40. Treatment: 3. LASIK LASIK can correct up to 4 D (But some latest instruments claim more correction) 9 Sept 2019 (LIONS) 40 [email protected]

41. Treatment: 4 Conductive keratoplasty (CK) Conductive keratoplasty (CK) involves the application of radiofrequency energy to the corneal stroma and can correct low–moderate hypermetropia and hypermetropic astigmatism. 9 Sept 2019 (LIONS) 41 [email protected]

42. Myopia or Short sightedness 1) Mild myopia includes powers up to -3.00 (D) 2) Moderate myopia, values of -3.00 to -6.00D 3) High myopia is usually myopia over -6.00D 9 Sept 2019 (LIONS) 42 [email protected]

43. What is Myopia? When parallel rays of light from infinity comes to a focus in front of the retina when accommodation is at rest. 9 Sept 2019 (LIONS) 43 [email protected]

44. Etiological Classification Axial myopia. Curvature myopia. Index myopia. Simple or physiological myopia Pathological myopia 9 Sept 2019 (LIONS) 44 [email protected]

45. There are some other myopia which is not worldwide accepted but some books discuss about it so you have to know some 9 Sept 2019 (LIONS) [email protected] 45

46. 9 Sept 2019 (LIONS) [email protected] 46 Features School Myopia College myopia Types of myopia Simple Simple Age of onset First decade 2 nd half of 2 nd decade Increment of power -0.5 - -1.0 D/yearly Not much Stabilization -5.0 to -6.0 D -2.0 to -2.5 D Astigmatism Less common Frequent Stabilize by 17 – 18 year 22 – 25 year Comparison between school myopia & College myopia

47. Pathological myopia Pathological or degenerative myopia is characterized by progressive anteroposterior elongation of the scleral envelope associated with a range of secondary ocular changes , principally thought to relate to mechanical stretching of the involved tissues. It is significant cause of legal blindness, with maculopathy the most common cause of visual loss 9 Sept 2019 (LIONS) [email protected] 47

48. Pathological myopia: Associations with Other Conditions a) Down’s Syndrome, b) Ocular Albinism, c) Infantile Glaucoma, d) Marfan’s Syndrome, e) Retinopathy of Prematurity , f) Ehler’s-Danlos Syndrome, g) low birth weight , and h) maternal alcoholism.   Patients with these diseases or conditions should be considered “at risk” for pathological myopia and carefully monitored. 9 Sept 2019 (LIONS) [email protected] 48

49. Pathological myopia: Staphylomas Pathological myopia causes the eye to elongate, which in turn stretches and thins the retina and the sclera of the eye. This leads to a bulging of the posterior portion of the eyeball. This condition is called a staphyloma.  By the age of sixty, 50% of patients with staphylomas in both eyes will be legally blind.  9 Sept 2019 (LIONS) [email protected] 49

50. Pathological myopia : Myopic Macular Degeneration As the eyeball grows and stretches, it may also cause an area of atrophy and/or cracks in the layers under the retina. These cracks can serve as conduits for abnormal blood vessels to grow under the retina. These vessels can hemorrhage and scar and is called Fuch’s spots. 9 Sept 2019 (LIONS) [email protected] 50

51. Pathological myopia : Fuchs spot What is Fuchs spot? It is a raised, circular, pigmented lesion at the macula developing after a subretinal hemorrhage has absorbed. Fuch’s spots, often occur in the 4th to 6th decades of life.  Approximately 5% of pathological myopia patients develop Fuch’s spots, which lead to damage in the macular region of the eye and a subsequent loss of central vision.  9 Sept 2019 (LIONS) [email protected] 51

52. Pathological myopia : Retinal Detachment The thinning of the layers of the eye may lead to degenerative changes in the peripheral retina including retinal holes and lattice degeneration which puts one at high risk for a retinal detachment.  If retinal breaks develop, fluid may leak behind the retina causing it to detach. 9 Sept 2019 (LIONS) [email protected] 52

53. Pathological myopia : Glaucoma The incidence of glaucoma may increase due to alterations of the drainage angle of the eye causing which causes an increase in the fluid pressure of the eye. Detection of glaucoma may be more difficult due to change of CCT, The thickness of the patient’s eyeglass lenses may impair visual fields testing, which is imperative in monitoring glaucoma. 9 Sept 2019 (LIONS) [email protected] 53

54. 9 Sept 2019 (LIONS) [email protected] 54 TIGROID FUNDUS  As the eye enlarges, the retinal pigment epithelium thins, resulting in a tessellated (checkered) appearance of the fundus and increased visibility of the choroidal vasculature.

55. 9 Sept 2019 (LIONS) [email protected] 55 POSTERIOR STAPHYLOMA :  Staphylomas are localized ectasia (“enlargement”) of the sclera, choroid, and RPE. It can be easily seen on a B-scan or CT Scan. Staphylomas can eventually lead to atrophy and loss of vision.

56. 9 Sept 2019 (LIONS) [email protected] 56 FUCHS SPOTS :  Fuchs spots are dark spots due to RPE hyperplasia. They can involve subretinal neovascular membrane with an overlying retinal pigment epithelial hyperplasia. The CNV can eventually cause disciform scars on the macula in the 4th-6th decade of life.

57. 9 Sept 2019 (LIONS) [email protected] 57

58. 9 Sept 2019 (LIONS) [email protected] 58 LACQUER CRACKS :  Lacquer cracks are spontaneous ruptures of the elastic lamina of Bruch’s membrane that appear yellowish-white and are usually located in the posterior pole. They generally have linear or stellate patters. IVFA will show hyperfluorescence as the fluorescein leaks through Bruch’s membrane, highlighting these cracks. These can lead to CNV in the 4th-6th decade of life

59. 9 Sept 2019 (LIONS) [email protected] 59 Lattice with atrophic hole

60. 9 Sept 2019 (LIONS) [email protected] 60 LATTICE DEGENERATION : Lattice degeneration is a vitreo -retinal degeneration that causes retinal atrophy (“thinning”). It can be classified as pigmented or non pigmented. It takes on a lattice formation (“crisscrossing”) because the retinal vessels become sclerotic, and the collagen is laid down in this crisscross pattern. Due to the retinal thinning, it is prone to causing retinal breaks, tears, or holes, which could potentially lead to retinal detachment. However, it is important to remember that retinal breaks due to lattice degeneration rarely turn into retinal detachments.

61. Treatment of pathological myopia: Spectacle The lenses may be extremely thick and heavy. Fortunately, we are able to use small eyeglass frames combined with high index lenses to make the lenses thinner, lighter and more cosmetic.  9 Sept 2019 (LIONS) [email protected] 61

62. Treatment of pathological myopia: Contact Lenses Contact lenses have been a good option for high myopes for many years. It eliminates the weight and thickness of the lenses in eyewear. It also eliminates the side vision difficulties inherent in these thick lenses. Myopic patients usually report having better vision when wearing contact lenses, because of eliminating the problems that the eyewear causes. 9 Sept 2019 (LIONS) [email protected] 62

63. Treatment: Refractive Surgery / LASIK LASIK or laser refractive surgery has not been as effective in the highly myopic corrections, as it has in the lower ranges of myopia. 9 Sept 2019 (LIONS) [email protected] 63

64. Treatment: surgery “Bear Claw” intraocular lens implant. It is affixed in the anterior chamber through a simple incision and can correct extreme amounts of myopia.  A clear lens extraction may be performed. The procedure is identical to a cataract extraction. The patient’s lens is removed, but an intraocular lens in not inserted. By removing the lens, about fifteen diopters of myopia is automatically corrected. 9 Sept 2019 (LIONS) [email protected] 64

65. Low Vision Considerations Most patients respond well to low vision care and low vision aids including magnifiers and CCTVs. These patients often present with mild photophobia and benefit from sunglasses. Patients with retinal detachments, myopic macular degeneration and staphylomas may have a poorer prognosis depending upon the location of the problem. 9 Sept 2019 (LIONS) [email protected] 65

66. Safety Issues – Physical Education Patients should not participate in any physical activities that can lead to jostling or trauma to the eye. Contact sports and ball sports are too dangerous. Even activities like jumping rope or volleyball can lead to a retinal detachment. Children should not participate in physical education or competitive sports without the prior review. 9 Sept 2019 (LIONS) [email protected] 66

67. Knowing the Signs of Retinal Detachment Every patient with pathological myopia must know the signs of a retinal detachment. These include the sudden appearance of flashes of lights, like lighting flashes. Also floaters, little shadowy dots, and/or cobwebs, shadowy strands could be the first sign of an impending retinal detachment or a tear of the retina. 9 Sept 2019 (LIONS) [email protected] 67

68. Difference between simple and pathological myopia Simple myopia Relatively stationary Less than 6 D. No pathological change present. No family history present. Pathological myopia Progressive in nature More than 6 D Pathological change present Family history 9 Sept 2019 (LIONS) 68 [email protected]

69. Various Types of Myopia Acquired Myopia Pseudo-Myopia. Space Myopia Night or Twilight Myopia. 9 Sept 2019 (LIONS) 69 [email protected]

70. Acquired myopia Acquired myopia can result from injury to the eye. Concussion will sometimes cause a loss of the anterior chamber. Partial dislocation of the lens forward. Induced myopia is seen after glaucoma operation. Injury may also cause the lens to increase its water volume producing myopia. 9 Sept 2019 (LIONS) 70 [email protected]

71. Pseudo-myopia Spasm of the ciliary muscle and of accommodation can occur in uncorrected hypermetropia or in early presbyopia; myopia results and it is noticeable that in this form of myopia there is poor accommodation and usually severe eyeache and headache. 9 Sept 2019 (LIONS) 71 [email protected]

72. Space myopia This condition is experienced when the individual has no stimulation for distance fixation. The eyes tend to choose a near fixation plane which can be very variable. The degree of myopia due to this condition is never more than -0.75 to -1.50 Dsph. It is particularly troublesome to aviators when flying in cloud or fog or at night. 9 Sept 2019 (LIONS) 72 [email protected]

73. Night or Twilight Myopia Short sighted patients often complain that they cannot see well in the distance at dusk or at night, especially when driving, although their spectacles give them good vision during daytime. 9 Sept 2019 (LIONS) 73 [email protected]

74. There are 4 possible explanations; Color shift: At night fall the blues & yellow are clearly seen but red & green very badly; thus the shorter wavelengths must be brought to a focus in dim light. Spherical aberration: The peripheral rays are more refracted. 9 Sept 2019 (LIONS) 74 [email protected]

75. Depth of focus: This is the greatest with a constricted pupil and it is much reduced with pupillary dilation, Accommodation will cause a spurious myopia, especially in young nervous persons who peer into darkness. This is noted in pilots who lack any distance object on which to focus. 9 Sept 2019 (LIONS) 75 [email protected]

76. Treatment of Myopia: 1. Spectacle For most people with myopia, eyeglasses are the primary choice for correction. Depending on the amount of myopia, one may only need to wear glasses for certain activities, like watching a movie or driving a car. Or, if very nearsighted, may need to wear them all the time 9 Sept 2019 (LIONS) 76 [email protected]

77. Treatment of Myopia: 2. Contact lenses.   For some individuals,  contact lenses offer clearer vision and a wider field of view than eyeglasses. However, since contact lenses are worn directly on the eyes, they require  proper care  to safeguard eye health. 9 Sept 2019 (LIONS) 77 [email protected]

78. Treatment of Myopia: 3. Ortho-k Another option for treating myopia is  orthokeratology ( ortho -k) , also known as corneal refractive therapy (CRT). In this nonsurgical procedure, patient wear a series of specially designed rigid contact lenses to gradually reshape the curvature of cornea. The lenses place pressure on the cornea to flatten it. Overnight, wear and then remove. People with moderate myopia may be able to temporarily obtain clear vision for most of their daily activities. 9 Sept 2019 (LIONS) 78 [email protected]

79. Treatment of Myopia: 4. Radial Keratotomy 9 Sept 2019 (LIONS) 79 [email protected]

80. Treatment of Myopia: 5. Laser procedures. Laser procedures such as LASIK (laser in situ keratomileusis ) PRK (photorefractive keratectomy) are also possible treatment options for myopia in adults. PRK was the first kind of corrective eye surgery to use a laser rather than a blade to remove corneal tissue. PRK became less and less popular following the development of LASIK 9 Sept 2019 (LIONS) 80 [email protected]

81. ASTIGMATISM 9 Sept 2019 (LIONS) [email protected] 81

82. ASTIGMATISM: DEFINITION When parallel rays of light from infinity comes to focus at different meridian of retina when accommodation is at rest. 9 Sept 2019 (LIONS) [email protected] 82

83. ASTIGMATISM : CLASSIFICATION Regular astigmatism Irregular astigmatism 9 Sept 2019 (LIONS) [email protected] 83

84. ASTIGMATISM: Classification Regular Astigmatism: When two meridians are at right angles to each other and the astigmatism can be fully corrected by spectacles. When the meridians are not at 90 0, it is often called oblique astigmatism although two axes are at right angles to each other. 9 Sept 2019 (LIONS) [email protected] 84

85. ASTIGMATISM: Classification Irregular astigmatism: In Irregular astigmatism, there are irregularities in the curvature so that no geometrical figure is adhered to. It does not tend itself to adequate correction by spectacles. Example: Keratoconus, corneal opacity R X : It can’t be corrected with spectacle so RGP Contact lens is the treatment of choice 9 Sept 2019 (LIONS) [email protected] 85

86. Regular astigmatism: Classification Regular astigmatism can be classified in various way: According to steepness of vertical meridian With the rule astigmatism Against the rule astigmatism 9 Sept 2019 (LIONS) [email protected] 86

87. 9 Sept 2019 (LIONS) [email protected] 87

88. According to relation of the two axes: At right angles to each other: Oblique astigmatism Not at right angles to each other: 9 Sept 2019 (LIONS) [email protected] 88

89. 9 Sept 2019 (LIONS) [email protected] 89 At right angles to each other: Oblique astigmatism

90. 9 Sept 2019 (LIONS) [email protected] 90

91. c ) According to type of error of refraction: Myopic Hypermetropic Combination (P.K Mukherjee: p 94) (But this classification is not widely accepted) 9 Sept 2019 (LIONS) [email protected] 91

92. ASTIGMATISM: Classification d) According to position of image in relation to the retina: Simple. Compound Mixed. (This is the most widely and well-accepted classification) 9 Sept 2019 (LIONS) [email protected] 92

93. Simple myopic astigmatism Simple h ypermetropic astigmatism Compound myopic astigmatism Compound hypermetropic astigmatism Mixed astigmatism 9 Sept 2019 (LIONS) [email protected] 93

94. Simple regular astigmatism Where one of the foci falls upon the retina, the other focus falls in front or behind the retina, so that while one meridian is emmetropic, the other meridian is hypermetropic or myopic. These are respectively designated as: a. Simple hypermetropic astigmatism. b. Simple myopic astigmatism. 9 Sept 2019 (LIONS) [email protected] 94

95. Simple hypermetropic astigmatism & Simple myopic astigmatism. 9 Sept 2019 (LIONS) [email protected] 95

96. Compound hypermetropic astigmatism. & Compound myopic astigmatism. Neither of the two foci lies upon the retina but are placed both in front or behind it. The state of the refraction is then entirely hypermetropic or myopic. Thus they are: a. Compound hypermetropic astigmatism. b. Compound myopic astigmatism. 9 Sept 2019 (LIONS) [email protected] 96

97. Compound hypermetropic astigmatism. & Compound myopic astigmatism. 9 Sept 2019 (LIONS) [email protected] 97

98. Mixed astigmatism 9 Sept 2019 (LIONS) [email protected] 98 Where one focuses in front and the other behind the retina, so that the refraction is hypermetropic in one direction and the myopic in other

99. OSPE: 2 A girl of 18 years-old came to you with -15.0 Dsph/-4.50 Dcyl 170 (R/E) and -17.0 Dsph/-5.0 Dcyl 180 (L/E) for LASIK surgery. Her BCVA is 6/18 and 6/36 respectively Now you have to counsel him about her desire, life style and future plan. 9 Sept 2019 (LIONS) [email protected] 99

100. Guideline of OSPE: 2 Ask why LASIK is important to her? Contraindication of LASIK in this case Can try contact lens but not regular (RGP) Surgical option at there but mention the side effects Discuss safety profile of her life style Discuss warning sign of RD Discuss LVA (may need in future) If unmarried, not to marry other myopic 9 Sept 2019 (LIONS) [email protected] 100

101. OSPE: 3 Calculate the spherical equivalent, do the simple transposition & mention type of astigmatism of the following prescriptions: +2.00 /―3.00 X 80 ―3.00 / + 2.00 X 90 +1.50 /― 3.00 X 45 Plano /―1.50 x 90 9 Sept 2019 (LIONS) [email protected] 101

102. Spherical equivalent: +2.00 /―3.00 X 80 +0.50 b) ―3.00 / + 2.00 X 90 -2.00 c) +1.50 /―3.00 X 45 Plano d) Plano /―1.50 x 90 -0.75 9 Sept 2019 (LIONS) [email protected] 102

103. Simple transposition a )+2.00 /―3.00 X 80 ANS: -1.00/+ 3.00 X 170 b) ―3.00 / + 2.00 X 90 ANS: -1.00/-2.00 X 180 9 Sept 2019 (LIONS) [email protected] 103

104. Simple transposition c) +1.50 /―3.00 X 45 ANS: -1.50/+3.00 X 135 d) Plano /―1.50 x 90 -1.50 /+ 1.50 x 180 9 Sept 2019 (LIONS) [email protected] 104

105. Type of astigmatism +2.00 /―3.00 X 80 9 Sept 2019 (LIONS) [email protected] 105

106. Type of astigmatism b) ―3.00 / + 2.00 X 90 9 Sept 2019 (LIONS) [email protected] 106

107. Type of astigmatism c) +1.50 /―3.00 X 45 9 Sept 2019 (LIONS) [email protected] 107

108. Type of astigmatism Plano/―1.50 x 90 9 Sept 2019 (LIONS) [email protected] 108