1. اصلاح میوپی کم و متوسط
A.Hekmatiyan MD
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2. If the power of an eye is too strong for its size, we say that the eye is myopic or "nearsighted. A myopic eye, then, has its located somewhere in front of the retina - the more in front it is, the greater the myopic refractive error.
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3. Myopia
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4. RETINAL REFLEX MOVEMENT
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6. DEFINITION ASSOCIATED FEATURES
Contact lenses are visual devices that provide an artificial aneterior refracting surface to the human eye and aer used for corrective , cosmetic and therapeutic purposes
ASSOCIATED FEATURES
Corneal and conjunctival tissue problems.
• Common categories include superficial punctate keratopathy edema, microcysts, infiltrates, hyperemia, neuwvascualrization
megathism, blebs, and giant papillary conjunctivitis
• Mechanical or physical problems include
visual flare, aberrations, magnification,accommodation congvergence.
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7. Corneal and Conjunctival Tissue Problems
Given here are very brief discussions of the more common corneal and conjunctival tissue problems related to contact lens wear.
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8. SUPERFICIAL PUNCTATE KERATOPATHY
Corneal staining
occurs when sodium fluorescein is retained in gaps on the epithelial surface; these are caused by the absence, damage, displacement, or breakdown of cells. Staining related to contactlenses commonly results from mechanical trauma, exposure desiccation, metabolic interference, or chemical toxicity and/or hypersensitivity. Mild staining may be asymptomatic, but as the epithelial disruption increases, discomfort,. pain, increased lacrimation, and photophobia are reported. With extensive and deeper epithelial disruption, fluorescein may enter the corneal stroma.
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9. Mechanical trauma may be caused by a foreign body while it moves between the contact lens and the cornea; by a foreign body that wedges against the cornea by a torn scratched, or coated contact lens or by fingernails during lens insertion or removal. Metabolic interference caused by hypoxia may break down or change the selective permeability of epithelial cells over a wide corneal area.
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10. Exposure desiccation with corneal lenses may result in staining around the 3 and 9 o'clock positions or inferior corneal areas. Chemical toxicity and/or hypersensitivity staining is most often a result of reactions against contact lens solutions or lens deposits and substances adherent to the deposits. Severe epithelial disorder associated with solution toxicity and/or hypersensitivity can result in pseudodendrites, which appear as raised gray epithelial plaques with serpentine shapes and light staining, or superior limbic keratoconjunctivitis, which is manifest as an inflammatory reaction of the superior cornea and adjacent bulbar conjunctiva
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11. A deep or broad area of epithelial disruption reduces the epithelium's ability to function as a barrier to infection, which may lead to ulcerative keratitis. The incidence of microbial keratitis is very small with DW, RGP corneal or soft contact lenses but it is much greater with soft EW lenses, for which Pseudomonas aeruginosa is the pathogen most frequently involved.
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14. EDEMA
Hypoxia is the primary reason for corneal stroma edema induced by contact lens wear, but a hypotonic preocular tear film may also contribute. With PMMA or very low Dkj L RGP corneal lenses, edema is manifest as a gross, circumscribed, whitish gray area.33 Termed central circular clouding, it appears around the point at which the center of the optic zone positions in primary fixation. To view it, a split-limbal technique is used with the slit-lamp biomicroscope; the area in question is viewed by the practitioner not looking through the microscope and against the black background of the pupil.
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15. As the central circular clouding moves from grade 1 to grade 3, the coloration deep ens, the borders become more distinct, and the epithelium stains. With soft contact lenses, edema does not present clinically as central circular clouding but rather is detected by the appearance of striae in the posterior stroma when the corneal thickness has increased by about 6% and of endothelial folds when corneal thickness has increased by about 10% or more Rigid or soft DW lenses seldom change corneal thickness to these degrees, with the exception of PMMA lenses, but the vast majority of patients who use soft EW lenses awaken with at least a 10% corneal thickness increase.
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16. Striae are fine,grayish white, short lines in the posterior stroma
Striae are fine,grayish white, short lines in the posterior stroma. It is believed that these are the result of a refractive effect that arises from the a fluid separation of vertically orientated collagen fibrils and pos terior stroma. Endothelial folds appear as a "buckling" of the posterior corneal layers; when observed with specular reflection they appear as dark lines and with direct illumination as bright lines
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17. MICROCYSTS
Microcysts induced by contact lens wear are probably pockets of dead cellular material that form adjacent to intraepithelial sheets at the epithelium's basement membrane these are clinical evidence of disorganized cell growth that results from significant hypoxia.
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18. They appear as small and irregularly scattered dots, which must be differentiated from dimple indentation and vacuole fluid pockets. Microcysts very frequently accompany soft EW lens use but may not be manifest for the first several months. As microcysts work through the epithelial surface, corneal staining is seen. When soft lens EW is discontinued, the number of microcysts initially increases and then diminishes until elimination, over about 2 months
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19. INFILTRATES.
Infiltrates induced by contact lens wear are accumulations of white blood cells between the corneal stroma's collagen fibers; the accumulation occurs as a result of hypoxia, chemical toxicity and/or hypersensitivity.
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20. The infiltrates appear as white or whitish gray, single or multiple foci in the anterior stroma; more often, they are located toward the limbus. Small or few infiltrates may be asymptomatic, but greater infiltration causes discomfort, pain, photophobia, and lacrimation. Superior limbic keratoconjunctivitis is accompanied by many microinfiltrates in the superior cornea. In conlact lens acute red eye syndrome, there are larger infiltrates on various segments of the peripheral cornea.
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21. HYPEREMIA AND NEOVASCULARIZATION
Sectorial hyperemia usually accompanies 3 and 9 o'clock desiccation staining and peripheral corneal infiltrates, ulcers, or abrasions. More generalized circumcorneal hyperemia may be caused by hypoxia and other inflammatory stimuli (e.g., chemical, osmotic, and physical). Adjacent to the limbus, a normal area of physiological edema occurs and within this is the normal corneal vasculature, which typically extends a little further onto the superior cornea. The rest of the cornea is avascular because its structure is too compact to allow vessel growth.
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22. However, degradation of corneal metabolism and its sequela of edema loosen the structure with the result that neovascularization may occur from secondary stimuli. Neovascularization related to contact lens wear involves the superficial vessels much more often than the deeper vessels39 It is uncommon for neovascularization induced by contact lenses to extend onto the cornea by more than 2-3mm.
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23. After proper management, the vessels empty, but the vessel wall remains. These ghost vessels appear as faint white lines when observed with indirect illumination, and they remain for years. Subsequent mild stimuli may refill the vessels with blood.
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24. POLYMEGATHISM AND BLEBS
Sufficient hypoxia and chronic corneal acidosis can cause variation in endothelial cell size (polymegathism), as viewed with specular reflection and very high magnification.After proper management to reduce or eliminate the causes, the endothelial mosaic usually normalizes.
Endothelial blebs constitute intracellular edema that develops with sufficient hypoxia and acidosis; they usually occur in unadapted soft lens wearers and may be a precursor of polymegathism. In specular reflection, blebs appear as black spots and resemble corneal guttae.
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25. GIANT PAPILLARY CONJUNCTIVITIS
Papillary conjunctivitis induced by contact lens wear is usually termed giant papillary conjunctivitis.It is caused primarily by mechanical irritation of the superior tarsal conjunctiva and secondarily by an autoimmune reaction to the patient's mucoproteins on the lens. Normal micropapillae have a diameter of less than O.3mm, macro papillae have a diameter of O.4-0.9mm, and giant papillae have a diameter of 1mm or greater.
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26. The enlarged papillae are collections of lymphocytes and plasma cells
The enlarged papillae are collections of lymphocytes and plasma cells. In addition to the enlarged papillae, papillary conjunctivitis induced by contact lens wear is characterized by hyperemia, reduced transparency, and increased production of mucus by the tarsal conjunctiva . Patients' symptoms include decreased comfort, increased lens movement, hazy vision, and itchiness. Signs and symptoms increase directly with the severity of papillary conjunctivitis. Mast cell stabilizers may be used to reduce symptoms, but elimination of the causes is necessary. This requires improved care of the lenses, more frequent lens replacement, and reduced wearing time.
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27. Silicone Hydrogel Lenses
The highly oxygen-permeable silicone hydrogel lenses have eliminated physiological changes resulting from hypoxia for a vast majority of patients. Overnight edema levels approximate those detected with no contact lens wear. Other hypoxia-related contact lens-induced tissue changes such as corneal striae, microcysts, and endothelial polymegathisms are rarely seen. Limbal redness, vascularization, and the myopic shift commonly observed with the wear of conventional soft EW lenses are reduced in incidence and severity
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28. Microbial keratitis is the most serious and potentially sightthreatening complication from contact lens wear. It is hypothesized that hypoxia from EW with conventional soft lenses leads to severe metabolic stress in the closed-eye environment. This produces a thin, weakened, poorly metabolizing epithelium, which in turn allows pathogenic microorganisms to invade the cornea and cause microbial keratitis. The high oxygen transmissibility of those silicone hydrogel lenses maintains a healthy corneal epithelium. Thus the eye's defenses are not compromised and protect against infection. Microbial keratitis is of much lower incidence with silicone hydrogel lenses compared with conventional soft lenses worn for EW.
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29. ACCOMMODATION AND CONVERGENCE
Lens effectiveness, which is a measure based on the distance of a correcting lens from the nodal point of the eye, produces a change in the amount of accommodation required to see at near with glasses compared with that with contact lenses. A myope who wears contact lenses must accommodate more than when wearing glasses. Conversely, a hyperope requires less accommodation with contacts than with spectaclesS2 This must be considered when an individual with marginal accommodative insufficiency, such as an incipient presbyope, is being fitted.
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30. Convergence requirements are altered when a change is made from glasses to contact lenses. A myope, when converging through spectacles, has an induced base-in effect and has to cone verge more than is required with contact lenses. A hyperope, on the other hand, has a base-out effect when converging through glasses and requires less convergence effort than is required with contact lenses. Contact lenses, because they remain centered on the eye, do not induce any prismatic effect upon convergence.
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31. Laser Subepithelial Keratomileusis (LASEK)
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32. INTRODUCTION
In laser subepithelial keratomileusis (LASEK), loosening and replacing the corneal epithelium can be performed using several techniques.I,3-8 Photo refractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) are currently the most popular procedures in refractive surgery. PRK is a relatively safe procedure; its major limitations are postoperative pain, subepithelial haze and prolonged visual rehabilitation. The epithelial removal (done prior to laser ablation in PRK is believed to be the major a factor contributing to these drawbacks.
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33. LASIK offers more comfort, faster visual rehabilitation, and minimal haze, but it has its own set of complications, predominantly related to the flap. These include free caps, incomplete pass of the microkeratome, flap wrinkles, epithelial ingrowth, flap melt, interface debris, and diffuse lamellar keratitis.
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34. In selected patients for whom PRK would be the recommended procedure, such as patients with thin corneas, patients with lifestyles or professions that predispose to flap trauma in eluding ,athletes in contact sports and military personnel, and patients with low myopia who are at a lower risk for subepithe lial haze, laser epithelial keratomileusis (LASEK)may be a viable alternative. 1,2.9
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35. LASEKtheoretically offers the advantage of avoiding the flap complications of LASIKand also addresses the drawbacks of discomfort and delayed recovery associated with conventional PRK. Epithelial sheet viability and adhesion are the basis for achieving the potential advantages of In patients with corneal pachymetry of 500 or lower
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37. SURGICAL TECHNIQUE
A sterile drape is placed around the eye. Then one drop each of topical 0.5% proparacaine (Ophthetic; Allergan, Irvine, CA) and 4% tetracaine (formulated in the MEEI pharmacy) are in- stilled and a lid speculum applied. The cornea is marked with overlapping 3mm circles around the corneal periphery, simulating a floral pattern. Gentle pressure was applied on the cornea while the barrel of the optical zone marker was filled with two drops of 18 % ethanol . after 25 seconds ethanol is absobed using weckcell
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38. Modified Vannas scissors are inserted under the epithelium and traced around the delineated margin of the epithelium, leaving 2-3 clock hours of intact margin, preferably at the 12 o'clock position. The loosened epithelium is peeled as a single sheet using a blunt spatula or a Merocel sponge, leaving a flap of epithelium with the hinge still attached. The laser ablation is initiated immediately thereafter using an excimerlaser. After ablation, a 30-gauge anterior chamber cannula is used to hydrate the stroma and epithelial flap with balanced salt solution. The epithelial flap is replaced on the stroma us- ing the straight part of the cannula under intermittent irrigation. Care is taken to realign the epithelium flap using the previous marks and to avoid epithelial defects. The flap is then allowed to dry.
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39. Intrastromal Corneal Ring Segments for Myopia
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40. INTRODUCTION
Intrastromal corneal ring segments (ICRSs), or Intacs, are placed in the peripheral stroma at approximately two-thirds depth, outside the central optical zone, to reshape the anteriorcorneal surface while maintaining the positive asphericity of the cornea. The first-generation design of Intacs was referred to as the 3600 intrastromal corneal ring (1CR). Tne current design consists of two segments, each with an arc length of 150’. Intacs are manufactured from polymethyl methacrylate (PMMA).
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41. Each Intacs segment has a hexagonal cross section that lies along a conic section. With a fixed outer diameter of 8.1 mm and an inner diameter of 6.8mm, Intacs leave a large, clear central optic zone. Each segment has a small positioning hole at the superior end to aid with surgical manipulation once the segments have been inserted. The two segments are designated as clockwise and counterclockwise to correspond to their orientation within the intrastromal tunnel.'
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42. Intacs change the arc length of the anterior corneal curvature
Intacs change the arc length of the anterior corneal curvature. The refractive effect achieved is directly related to the thichness of the product. Placing the product in the periphery of the cornea causes local separation of the corneal lamellae, which results in shortening of the corneal arc length. This has a net effect of flattening the cornea, thereby correcting for myopia by lowering the optical power of the eye. Increasing the thickness of Intacs causes greater degrees of local separation and increased corneal flattening. Thus, the degree of cornealllattening-or correction- achieved by lntacs is directly related to thickness.'
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43. lntacs are available in the United States in three different thick· nesses-0.25, 0.30, and 0.35mm-intended for the reduction or elimination of/Dw myopia . The initial enthusiasm regarding ICRSs for the correction of myopia has faded for multiple reasons, including a limited range of coection, induced astigmatism, and slow visual recovery. Although the future role of CRSs in refractive surgery is unclear, they may evolve into an important therapeutic intervention in keratoconus patients. Another potential application of CRSs may be to minimize the risk of corneal ectasia following laser in situ keratomileusis (LASIK in patients with high myopia.Intacs are also available in thicknesses of 0.40 and 0.45 to correct myopia up to -4.50D.
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44. CLINICAL OUTCOME
The more centrally placed incisions tended to cause more induced astigmatism, whereas more peripherally placed incisions tended to be vascularized." Transient loss of corneal sensation was noted 2 months postoperatively but returned to normal by 6 months."
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45. Gel Injection Adjustable Keratoplasty
A modification of rCRS surgery is gel injection adjustable keratoplasty. In this procedure, a delaminator is used to separate the stroma lamellae , This is followed by gel injection into the stromal channel. After polymerization, the gel induces central flattening, without significant postoperative inflammation this procedure may have potential advantages over lCRSs, but it has not been approved by the U,S, Food and Drug Administration,
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46. Automated and Manual Lamellar Surgical Procedures and Epikeratoplasty
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47. ضمن عرض پوزش
بدلیل حجم بالای LECTUER ادامه اسلایدها امکان پذیر نمیباشد در صورت نیاز به ادامه لطفا به واحد سمعی و بصری مرکز آموزشی درمانی فیض مراجعه و یا با شماره تلفن داخلی 392 تماس حاصل نمائید با تشکر