Refraction Errors Flashcards
Hypermetropia
Long sightedness, the parallel rays from infinity are focused behind the retina.
Etiology of Hypermetropia
Axial, Curvatural Index Absence of lens Positional
Axial Hypermetropia
Shortening of AP diameter
1mm- 3 D change in power
Curvatural
Flattening of curvature
1mm increase in radius- 6 D increase in power
Index Hypermetropia
Decrease in refractive index
Diabetes
Old age
Positional Hypermetropia
Occurs due to posteriorly placed crystalline lens
Hypermetropia due to absence of crystalline lens
Can be congenital or acquired
Acquired- surgically or due to posterior dislocation
Consecutibe hypermetropia
Occurs due to: over corrected myopia as in LASIK
Or due to underpowered intraocular lens implantation during cataract surgery
Clinical types of hypermetropia
1) Physiological/ developmental/ simple
2) non physiological
3) functional
Simple/ developmental hypermetropia
Developmental curvatural
Developmental axial
Types of Non physiological hypermetropia
Congenital
Acquired
Congenital non physiology hypermetropia is seen in
Microphthalmos Nanophthalmos Microcornea Congenital posterior subluxation of lense Congenital aphakia
Functional hypermetropia occurs due to
Paralysis of accommodation i.e paralysis of 3rd cranial nerve
Acquired non-physiological hypermetropia
Senile Acq curvatural Acq axial Aphakia Positional Consecutive Pseudoaphakic
What is meant by total hypermetropia
It is the total amount of refractive error. It is estimated after complete cycloplegia by atropine
