Transcript Myopia
Myopia Walter Huang, OD Yuanpei University Department of Optometry Definition The common name for this refractive error is near-sightedness Patients with myopia are known as myopes Definition When parallel rays of light enter the eye (with accommodation relaxed) and come to a single point focus in front of the retina Etiology Axial length The axial length of the eye is longer than normal due to imperfect emmetropization The most common cause of myopia for high myopes Etiology Refractive power The refractive power of the eye is too strong Curvature myopia Cornea or lens has a steep curvature (e.g., keratoconus) Increased index of refraction (e.g., cornea, lens) Anterior movement of the lens (e.g., nuclear sclerosis) Prevalence Age At birth: 24 to 50% As birth weight decreases, the amount of myopia increases in premature infants The mean refractive error for full-term infants is +2.00 D The prevalence of myopia decreases by 1 year old due to the process of emmetropization 5 to 6 years old: 2% (>-0.50DS) 13 to 14 years old: 15% Prevalence Age In Taiwan (1995) 7 years old: 12% 12 years old: 56% 15 years old: 76% 18 years old: 84% In western countries 20 years old: 20% Prevalence Gender In general, there are no significant differences between males and females Progression of myopia tends to begin and end earlier in females High myopia is more common in females Prevalence Ethnicity Higher prevalence in Asians, Arabs, and Jews Lower prevalence in Caucasians, Blacks, and South Sea Islanders Prevalence Urban versus rural communities Myopia is more common in urban communities than in rural ones Progression Myopia tends to increase linearly until the middle or late teenage years, at which point, it levels off The earlier a child becomes myopic, the more rapidly the condition tends to progress Juvenile-Onset Myopia Definition Myopia in which the age of onset is 8 to 12 years Juvenile-Onset Myopia Etiology Evidence for genetics influences Greater similarity of refractive error and ocular structures in identical twins than in fraternal twins Juvenile-Onset Myopia Etiology Evidence for genetics influences Increased prevalence of myopia in children of myopic parents Probability of a child being myopic is: 40% when both parents are myopic 20 to 30% when one parent is myopic <10% when neither parent is myopic Juvenile-Onset Myopia Etiology Evidence for environmental influences Association between near work, education, and myopia Children who do a lot of near work, like reading, tend to become myopic Myopia is more common where occupations require extensive near work Myopia and Visual Acuity Uncorrected VA Refractive Error (D) 20/30 0.50 20/40 0.75 20/60 1.00 20/80 1.50 20/120 2.00 20/200 2.50 Symptoms Blurry vision at distance Clear vision at near Squinting Occasional headaches Signs Decreased visual acuities at distance Clinical Tests Visual acuity tests - distance Retinoscopy Subjective refraction Management Divergent or minus lenses in spectacles or contact lenses Cycloplegics Surgery Refractive surgery Management Spectacles Single vision glasses Bifocal glasses More effective in children with near esophoria Management Contact lenses Soft contact lenses Rigid gas permeable contact lenses Ortho-keratology contact lenses Corneal reshaping therapy contact lenses Management Contact lenses Ortho-keratology Rigid gas permeable contact lenses are used to flatten the cornea Results are unpredictable (0 to 5.00 D of change) Two eyes may respond differently in anisometropia Procedure may induce astigmatism Retainer lens is required; otherwise, the patient’s prescription may return to normal Management Cycloplegics (e.g., atropine) Reduce the ability to accommodate May slow the progression of myopia Management Surgery Radial keratotomy (RK) Technique Eight cuts with a blade in a radial pattern are made on the surface of the cornea The depth of each cut is through approximately 85 to 90% of the cornea Management Surgery Radial keratotomy (RK) Post-surgical complications Hyperopic shift Diurnal fluctuations of refractive error and visual acuity Glare Corneal scarring Management Refractive surgery Photorefractive keratectomy (PRK) Technique High energy photons from an excimer laser are used to photoablate a small amount of tissue from the anterior corneal surface and sculpt the cornea Management Refractive surgery Photorefractive keratectomy (PRK) Post-surgical complications Eye pain Corneal disruption Blurry vision Prolonged duration of drug use Greater time needed for eyesight recovery Management Refractive surgery Laser in-situ keratomileusis (LASIK) Technique A microkeratome is used to cut a flap of superficial corneal tissue The flap is lifted back, exposing the underlying corneal stroma The excimer laser is used to perform tissue removal in the corneal stroma The flap is repositioned in its original position and adheres to the underlying corneal stroma without the need for sutures Management Refractive surgery Laser in-situ keratomileusis (LASIK) Post-surgical complications Severe dry eye syndrome Poor night vision Reduced contrast sensitivity Astigmatism Management Refractive surgery Points to consider after the surgical procedure Use eyedrops, as prescribed by the ophthalmologist Be careful not to allow chlorinated water , shampoo, and sweat to come into contact with the eyes Wear sunglasses when outside to protect the eyes from sunlight Remember to go back to the hospital for regular follow up visits with the ophthalmologist and to get eyedrops Pathological Conditions Associated with Myopia Cataract Nuclear cataract causes a myopic shift Pathological Conditions Associated with Myopia Diabetes High blood glucose levels cause increased sorbital levels in the lens Water rushes in and dilutes the sorbital in the lens Lens bulges and results in a myopic shift Pathological Conditions Associated with Myopia Marfan’s syndrome Suspensory ligaments break Subluxation of lens occurs superiorly and temporally and results in a very high increase in myopia