1 Refractive error and presbyopia Flashcards
Infant emmetropization:
Cornea/lens power decreases / eye elongates.
+2D at birth, changes over 2 years
Ocular components in hyperopia:
Short axial length, flat cornea, weak lens power
Hyperopia visual symptoms:
Blurred vision, asthenopia, binocular disfunction, amblyopia, strabismus
Myopia onset classification:
Syndromic (part of systemic disease)
Congenital (infants)
Juvenile-onset (most common)
Adult onset (dysregulated axial growth)
Myopia visual impairment risks
Greater risk <-6.00D Retinal detachment Myopic maculopathy Glaucoma Cataracts
Types of astigmatism
With the rule (steep curve ~90/cyl x 180, common 18-40y)
Against the rule (curve ~180, common 0-18y, 40-X)
Oblique (diagonal curve)
Active emmetropization processes and spectacle correction
Defocus on retina detects/decodes blur
Glasses results in lesser emmetropization and hyperopia
Prevalence of refractive error:
Astigmatism 0.5D > hyperopia 2D / Myopia -0.5D
Myopia prevalence
Greater in females, greater in Asia 36-50% M/F 5-15 years
Lesser in scandinavia 13% M/F 16-19
Myopia progression
Appears a 7years. Progresses till 21 years
Emmetropization and myopia development factors:
Accomodative lag (hyperopic defocus = elongation)
Vergence (base in prism for myopia control)
Peripheral/global has most relevance (defocus triggers elongation or stop)
Red/blue light (variable effect)
Pregnant smoking
Maternal age > 35
Myopia control
OrthoK lenses / MF CLs / Atropine(peripheral blur)
Outdoor presence without base myopia(1h/week = 2% myopia loss)
Gaze breaks + longer working distance (decreased accomodative lag)
Presbyopia (accomadative amplitude) with age:
10 AA~12D
40 AA<3D (presbyope)
50 AA~0D
Spherical change with age to 80
0 = +2D 2 = +1D 40 = 0D 70 = 1D 80 = 0D
Age effects on CL wear
Eyelid aperature decrease
Decreased lacrimal secretion
