1. Refractive Errors and management

2. Vergence
Parallel Beam
Convergence
Divergence

3. VERGENCE All naturally occurring sources of light are divergent
Light rays traveling parallel have zero vergence
Light rays that focus on a point are convergent
The unit of measurement of vergence is the diopter
D= Vergence (Diopters)=___________1_____________
Distance from the source in meters

4. BASIC OPTICS Therefore:
The closer the light is to its source, the greater the vergence
The farther the light is from its source, the lower the vergence, approaching zero as distance goes toward infinity.
Diverging light has negative power (-)
Converging light has positive power (+)
Lens power is calculated by : using the biometry by measuring the axis length and the corneal convexity.

5. REFRACTION
Refraction of light occurs when light passes from one medium to another of different refractive index (ie. density)

6. Refractive Components of the Eye
Cornea: responsible for the majority of the refractive power of the eye (40 D) / constant.
Lens: 20 D of refractive power, changes with accommodation.
Axial length is constant except under certain conditions

7. These two refracting elements in the eye converge the rays of light because:
1-The cornea has a higher refractive index than air; the lens has a higher refractive index than the aqueous and vitreous humours that surround it.
2-The refracting surfaces of the cornea and lens are spherically convex

8. Fovea
Light rays

9. Emmetropia (normal vision)
Adequate correlation between axial length and refractive power.
Parallel rays of light from a distant object are brought to focus on the retina with the eye at rest (no accommodation) ,such an individual can see sharply in the distance without accommodation.

10. Ametropia (Refractive error)
Mismatch between axial length and refractive power.
Parallel light rays don’t fall on the retina with the eye at rest (a change in refraction is required to achieve sharp vision).
Ametropia may be divided into:
Nearsightedness (Myopia)
Farsightedness (Hyperopia)
Astigmatism
Presbyopia

11. Accommodation Emmetropic eye
object closer than 6 M send divergent light that focus behind retina , adaptative mechanism of eye is to increase refractive power by accommodation
Helm-holtz theory
contraction of ciliary muscle -->decrease tension in zonule fibers -->elasticity of lens capsule mold lens into spherical shape -->greater dioptic power -->divergent rays are focused on retina
contraction of ciliary muscle is supplied by parasympathetic third nerve.

12. Myopia Parallel rays converge at a focal point anterior to the retina
Etiology : not clear , genetic factor
Causes
excessive long globe (axial myopia) : more common
excessive refractive power (refractive myopia).
Increase in the curvature of the cornea or the surfaces of the crystalline lens.

15. Uncorrected, light focuses in front of fovea
Corrected by divergent lens, light focuses on fovea

16. Myopia
The patient is able to focus on objects near but not far away (blurred distance vision).
Typical complaint is difficulty focusing on road signs or the black board.
Usually detected by the young when they discover they cannot see things at a distance as well as their friends do .
The teacher complains that the child makes too many mistakes copying things from the black-board.
The lens is unable to flatten enough to prevent conversion of images before reaching the retina.
Frequently squinting is compensatory mechanism in an attempt to improve uncorrected visual acuity when gazing into the distance.

17. MYOPIA
Increases with age roughly until the person stops growing in height.
A myopic person can still see some objects clearly, provided the object is closer than the far point
Pseudomyopia: accomodative spasm.The patient cannot relax accomodation when looking in the distance. For example, an over anxious student

18. Myopia Progressive and malignant myopia interchangeable
Forms
Benign myopia (school age myopia): Benign myopia usually starts in school, develops during adolescence period and finally stabilizes in the adulthood. It rarely grows beyond -7.0 D and it is never associated with any pathologic changes on the eye fundus.
Progressive and malignant myopia
interchangeable
myopia increase rapidly each year and is associated with vitreous opacities , fluidity of vitreous and chorioretinal change.

19. Myopia Congenital myopia Myopia > 10 D Increase slowly each year
Special forms
cataract nuclear sclerosis , keratoconus , spherophakia

20. Myopia Symptoms Amblyopia – uncorrected myopia > 10 D
Typically do not have “eye-strain”, “watering” of the eyes or headaches as often as hypermetropes do
• Usually detected by the young when they discover they cannot see things at a distance as well as their friends do
• The teacher complains that the child makes too many mistakes copying things from the black-board
Blurred distance vision
Squint in an attempt to improve uncorrected visual acuity when gazing into the distance
Headache
Amblyopia – uncorrected myopia > 10 D

21. Myopia Morphologic changes deep anterior chamber
atrophy of ciliary muscle
vitreous may collapse prematurely -->
opacification
fundus change : loss of pigment in RPE ,large disc and white crescent-shaped area on temporal side ,RPE atrophy in macular area , posterior staphyloma ,retinal degeneration-->hole-->increase risk of RD
Treatment : concave lenses, clear lens extraction
*Staphyloma : depression on retina.

22. PATHOLOGICAL CAUSES OF MYOPIA
KERATOCONUS

23. PATHOLOGICAL CAUSES OF MYOPIA
* Nuclear Cataract *Diabetes

24. PATHOLOGICAL CAUSES OF MYOPIA
Marfan’s Staphyloma

25. Complication of myopia 1-RD 2-Macular degeneration
Complication of myopia 1-RD 2-Macular degeneration. 3-Cataract 4-Open angle glaucoma.

26. Hyperopia
Parallel rays converge at a focal point posterior to the retina
Etiology : not clear , inherited
Causes:
excessive short globe (axial hyperopia) : more common
insufficient refractive power (refractive hyperopia)
Hyperopia forms a stage in normal development of the eyes—at birth eyes are hypermetropic (2.5 to 3.0 Diopters).
When persists in adulthood it represents an imperfectly developed eye.
Lens changes (cortical cataract).
Special forms : lens dislocation , postoperative aphakia

27. HYPEROPIA
• hyperopic persons must accommodate when gazing into distance to bring focal point on to the retina more than normal people .
Hyperopia may be partially compensated for by using the eyes’ accommodative ability this is possible during the first two to three decades of life
• When accommodative ability cannot keep up with demand, hyperopia is manifest and images are blurred in the distance and for near and the need for reading glasses arises earlier than in the normal person.
Typical complaint is difficulty reading.

28. Hyperopia Symptoms Typical complaint is difficulty reading
visual acuity at near tends to blur relatively early
nature of blur is vary from inability to read fine print to near vision is clear but suddenly and intermittently blur
blurred vision is more noticeable if person is tired , printing or inadequate light .
Extremely good distant vision (6/4)
asthenopic symptoms : eyepain, headache in frontal region, burning sensation in the eyes, blepharoconjunctivitis.
Young children with significant hypermetropia can also develop a convergent squint.
accommodative esotropia : because accommodation is linked to convergence -->ET
Amblyopia – uncorrected hyperopia > 5D

29. Hyperopia
Fundus in axial hyperopia may reveal pseudooptic neuritis (indistinct disc margin, no physiologic cup, maybe elevated disc)
DDx from optic neuritis by :>=4D, no enlarged blind spot, no passive congestion of vein
Treatment : convex lenses, keratorefractive surgery, refreactive lensectomy with IOL, phakic IOL

31. Uncorrected, light focuses behind fovea
Corrected by convergent lens, light focuses on fovea

33. PATHOLOGICAL CAUSES OF HYPEROPIA
DISLOCATED LENS

34. PATHOLOGICAL CAUSES OF HYPEROPIA
RETINAL DETACHMENT
RETINAL FLUID
1 mm = 3D
CHOROIDAL TUMOR

35. Complication .
They are more susceptible to closed angle glaucoma because there smaller eyes are more likely to have shallow A.C and narrow angles.

36. Astigmatism
Parallel rays come to focus in 2 focal lines rather than a single focal point
Etiology : hereditary
Cause : Astigmatism present when the cornea curvature is irregular (Refractive power of the cornea in different planes is not equal).
In short, astigmatism occurs whenever the vertical curvature of the cornea is different from the horizontal.

38. Astigmatism Classification
Regular astigmatism : power and orientation of principle meridians are constant
With the rule astigmatism , Against the rule astigmatism , Oblique astigmatism
Simple or Compound myopic astigmatism , Simple or Compound hyperopic astigmatism , Mixed astigmatism
Irregular astigmatism : power and orientation of principle meridians change across the pupil.

39. Keratoconus is pathological cause of irregular astigmatism
Simple astigmatisum : one focal point on retina other in front
Compound astigmatism : 2 points in front or 2 behind
Hypermetropic : 2 points behind retina.
Mixed : 1 point in front other behind.
With rule astigmatism : when the steeper meridian is vertical.
Against rule : when steeper meridian is horizontal .

41. Astigmatism Symptoms asthenopic symptoms ( headache , eyepain)
blurred vision
distortion of vision
head tilting and turning
Amblyopia – uncorrected astigmatism > 1.5 D
Treatment
Regular astigmatism :cylinder lenses with or without spherical lenses(convex or concave), Sx
Irregular astigmatism : rigid CL , surgery

42. Treatment of astigmatism
1. Laser, Intraocular toric lenses, Limbal relaxing incision
Contraindicated to do LASIK as it needs good thickness of cornea and regular curvature .

43. Pathologic Causes of Astigmatism
Corneal: post surgical, traumatic, infectious
External pressure on cornea: lid masses
Lens: pressure on lens from tumors

44. Presbyopia
Physiologic loss of accommodation in advancing age due to age related loss of elasticity of the capsule.
deposit of insoluble proteins in lens in advancing age-->elasticity of lens progressively decrease-->decrease accommodation.
Around 45 years of age , accommodation become less than 3 D-->reading is possible at cm-->difficultly reading fine print , headache , visual fatigue.
This occurs earlier in hypermetropes than myopes.

45. Presbyopia Treatment convex lenses in near vision Reading glasses
Bifocal glasses
Trifocal glasses
Progressive power glasses

46. Anisometropia Difference in refractive power between 2 eyes
refractive correction often leads to different image sizes on the 2 retinas( aniseikonia)
aniseikonia depend on degree of refractive anomaly and type of correction
closer to the site of refraction deficit the correction is made-->less retinal image changes in size ??

47. Anisometropia Glasses : magnified or minified 2% per 1 D
Contact lens : change in size less than glasses
Tolerate aniseikonia ~ 5-8%
Symptoms : usually congenital and often asymptomatic
Treatment
anisometropia > 4D-->contact lens
unilateral aphakia-->contact lens or intraocular lens

48. Diagnosis OF refractive errors :
not required
Diagnosis of refractive errors is made by an optician or ophthalmologist.
Instruments used to diagnose refractive errors include:
- pinhole glasses
- Autorefractor (measures how light changes as it enters the eye).
Retinoscope (measures the refractive condition of the eye).
- Phoropter.

49. View through an autorefractor
Pinhole glasses
Phoropter
View through an autorefractor

50. Pinhole Test
Light rays that are perpendicular to the lens do not refract , but go straight forward.
If visual acuity improves with the pinhole test, then this is a refractive error; if it worsens, then this is a central field defect.

51. Types of optical correction
Spectacle lenses
Monofocal lenses : spherical lenses , cylindrical lenses
Multifocal lenses
Contact lenses:
higher quality of optical image and less influence on the size of retinal image than spectacle lenses
indication : cosmetic , athletic activities , occupational , irregular corneal astigmatism , high anisometropia , corneal disease.
Can be: soft, hard, gas-permeable,toric

52. Contact lenses
disadvantages : careful daily cleaning and disinfection , expense
complication : infectious keratitis , giant papillary conjunctivitis , corneal vascularization , severe chronic conjunctivitis
Intraocular lenses
replacement of cataract crystalline lens
give best optical correction for aphakia , avoid significant magnification and distortion caused by spectacle lenses

53. Hard lenses:
Plastic polymer.
Most durable.
Rigid, therefore may scratch the cornea.
Not gas permeable  corneal hypoxia  corneal ulcers.
Cannot be worn continuously.
Difficult to get used to (because they are very rigid).
Less susceptible to infection and allergy.
Best for treating astigmatism (smoothes out the uneven curvature).

54. Hard contact lenses are used in orthokeratology: the fitting of a series of rigid contact lenses to reshape the cornea. It is an alternative to glasses and surgery

55. Soft lenses:
* High water content.
* Less durable.
* Permeable for both gases + liquids.
* Could be worn for long periods.
* Tolerated much better.
* They do correct astigmatism.(MILD ONE )
* Are the most comfortable lenses.
* Are the least durable lenses (must be replaced more often).
Susceptible to accumulation of deposits (because they absorb more water, which binds proteins). This accumulation of protein deposits leads to allergic conjunctivitis and other allergies.

56. Gas permeable lenses (Semi-rigid):
They are permeable only to gases.
They are more comfortable than hard lenses, but less than soft ones.
They are more durable than soft lenses, but less than hard lenses.
Allow oxygen to pass, but also allow proteins to deposit.

57. Toric lenses:
Are similar to soft contact lenses, but have a couple of extra characteristics:
They have 2 powers in them: 1 for spherical correction + 1 for astigmatism.
They are designed to keep the lens in a stable position even on movement.
They offer the comfort of soft lenses ,and at the same time they correct astigmatism, but their disadvantage is that the lens will sometimes rotate, and this creates a very irritating change in vision as the lens rotates.

58. Contraindications to using contact lenses:
* History of atopy.
* Dry eyes.
* Previous glaucoma filtration surgery.
* Inability to handle and cope with the lenses.

59. Refractive Surgery Techniques
Radial Keratotomy (RK) not used anymore.
Freeze keratomileusis not used anymore.
Photorefractive Keratectomy (PRK)
Laser Epithelial Keratomileusis (LASEK)
Laser-assisted in-situ Keratomileusis (LASIK)
Others:
Astigmatic Keratotomy (AK)
Intracorneal ring segments (Intacs)
Phakic Intraocular Lens Implants
Refractive lensectomy

60. Surgery classified into :
Flab : LASIK > and doing a flap needs good thickness of cornea and regular surface {so not made for keratoconus nor astigmatism} and being not susceptible to trauma after surgery unlike boxer or solider.
Surface ablation : SPRK (LASER) , LASEK > here we remove part of the regenerative epithelium .
LASIK has faster(2-3 days) post op recovery than Surface ablation(5-7days) .

61. Laser technology Excimer laser: EXCited dIMER
AKA “cool laser beam” because little thermal damage to adjacent tissues.
193nm wavelength ultraviolet laser with sufficient energy to disrupt intermolecular bonds within the corneal stromal tissue (photoablative decomposition).
First excimer lasers FDA approved in 1995, with beam width 4-5mm, now available less than 100 microns.
Each laser pulse removes a given volume of stroma
Three types of laser application: wide-area ablation, scanning slit, and flying spot lasers.

62. Laser technology
In myopia, laser flattens central cornea to decrease its focusing power to bring secondary focal point back to retina.
In hyperopia, the laser removes peripheral corneal tissue thereby secondarily steepening the central cornea, increasing the focusing power of the cornea.
Astigmatism treated with elliptical or cylindrical beams that flatten the steepest corneal meridian.
To minimize glare and halos, optical zone should be larger than the dilated pupil.

63. Myopic photorefractive keratectomy
PRK is recommended for some patients who cannot undergo LASIK. These include:
Patients whose corneas are too thin to have LASIK &Patients whose corneas are scarred (from infection or trauma).
PRK can effectively treat low to mod myopia or hyperopia +/- astigmatism.
Performed as outpt with topical anesthesia.
First, the corneal epithelium in the area to be ablated is removed to expose Bowman’s layer and the underlying corneal stroma (spatula, laser).
Excimer laser then applied as directed by the corneal topography-driven computer program.
Topical antibiotics, steroids, and NSAIDs applied, along with a bandage contact lens (BCTL)

64. PRK
In the post-op period, pt may experience tearing, photophobia, blurred vision, and discomfort due to abrasion of central epithelium.
This can be controlled with topical steroids and NSAIDs.
Pts occ. require systemic analgesia for severe pain
BCTL removed once epithelial defect healed (avg 3-4 days).
Abx continued several more days, and steroids for up to 3 months post-op.
Visual acuity improves once the epithelial defect heals, but fluctuates for a few months and finally stabilizes at ~3 months.
Glare, halos, and dry eye symptoms common in the first month post-op, usually diminishing/disappearing by 3-6 months.

65. Laser Sub-Epithelial Keratomileusis
LASEK can treat mild to moderate myopia and hyperopia +/- astigmatism.
Can be performed as an outpt with topical anesthesia
The corneal epithelium is incompletely incised using a microkeratome with a 70 micron deep blade.
A hinge is left at the 12 o’clock position.
Dilute alcohol (20%) drops are applied to the exposed tissue and left for ~30 seconds. The area is then washed with water and allowed to dry. The excimer laser is applied as in PRK to the sub-epithelial stroma.
The epithelial flap is repositioned afterward.

66. LASIK
The use of the suction ring helps hold the cornea steady and provides for a uniform cut by the microkeratome.
Flaps can be formed by an automated process involving a blade guide on the suction ring to guide a turbine-driven microkeratome, producing a very smooth, regular cut
Patients usually sent home on topical antibiotics, steroids, and NSAID drops
Benefits include little pain, quick recovery of vision, and potential to treat higher levels of myopia. LASIK enhancements are also easily performed.

67. LASIK

68. LASIK Complications Potential complications:
Intra-operative flap complications: microkeratome complication with a higher rate with surgeon inexperience
Post-operative flap complications
Flap-bed interface epithelialization: that epithelial growth at the interface could significantly be reduced by irrigating the stromal surfaces and using a BCTL for one day.
Irregular astigmatism
Infection:
Diffuse lamellar keratitis (DLK): (AKA Sands of Sahara syndrome) Wavy inflammatory reaction at LASIK flap interface 1-3 days post-op of unknown cause. Treatment involved high-dose topical steroids or lifting the flap to irrigating the interface.
Progressive corneal ectasia: progressive corneal thinning and steepening with worsening irreg. astigmatism thought to result from too thin a stromal bed after LASIK. Most believe stromal bed thickness should be at least 250 microns.

69. Implantable Contact Lenses:
Between iris + lens.
Preserves accommodation.
Complications include:
* Over correction.
* Under correction.
* Infection.
* Increased intraocular pressure.

71. Clear lens extraction + IOL:
IOL: Intra ocular lens.
Same as cataract extraction.
Implantation of artificial lens.
Lose accommodation (patient will need reading glasses).

74. 2 contraindications of refractive eye surgery
Keratoconus. Thin cornea. Pregnant. SLE, RA. Autoimmune disorders. Glaucoma. Diabetes.

75. Glasses:
Advg > comfortable , no risk for infection, or dryness or allergy.
Disadvg > cosmatic , poor quality of vision esp in high degree , not convenient for some jobs.
Contact lens :
Advg : cosmatic , good quality of vision , more convenient .
Disadvg : infection , allergy , dryness.