CLM - Mechanisms Regulating Ocular Growth and Refractive Error Development - Week 5 Flashcards
Define emmetropisation.
The disappearance of neonatal refractive errors which are considered normal
What is the approximate change in refraction from a newborn baby to 6-8 years of age?
From +2.00D to +0.25D
What is the average axial length of a neonatal and adult eyeball?
Neonatal - 16.5mm
Adult - 23.5mm
Describe the biological statistical method. List the four ocular components it proposes is involved in emmetropisation.
Attempts to show that all refractive errors re due to the way which the components of the eye combine:
Axial length
Corneal power
Lens power
Anterior chamber depth
Does the biological statistics method have strong evidence? Explain.
There is strong evidence to suggest there is coordinated growth of the eye
What does the biological statistics method propose about large eyes?
That they have flatter corneas
What does the biological statistics method suggest drives its proposed mechanism? Explain.
Hereditary influences
It doesnt explain the role of the environment
Describe the three factors of the theory of emmetropisation what theyre important.
It proposes that three factors explain all major correlations between an eyes optical components:
Size factor
Stretch factor
Derailment factor
Describe the size factor of the theory of emmetropisation, and describe where the loadings are (2).
Bigger eyes have flatter corneas
Loadings in corneal curvaure and axial length
Describe the stretch factor of the theory of emmetropisation, and describe where the loadings are (3).
Loadings in the vitreous chamber depth, axial length, and lens power
Describe the derailment factor of the theory of emmetropisation, and describe where the loadings are (1).
Loadings in all four
Describe what the theory of emmetropisation proposes.
The ciliary body and choroid form an elastic envelope that limits the stretch of the sclera by counteracting IOP.
The macula supplies information regarding focus to the brain, which feedbacks information concerning the necessary degree of stretch.
Does the theory of emmetropisation propose both hereditary and environmental influences?
Yesd
Describe the use-abuse theory.
Suggests that the ‘abuse’ of eyes in schooling causes myopia
What is the evidence for the association of near work and myopia in humans (2)?
Strong evidence esxists, but does not provide proof of cause and effect
What does the use-abuse theory strongly support; hereditary or environmental factors as the major influence on ametropia?
Environmental
Describe the effect of lid fusion on ocular growth when the subject is grown in both light and dark conditions.
Neonatal lid fusion causes elongation when the animals are grown in light conditions
There is no effect if grown in dark conditions
Define form deprivation myopia. What concept does this support?
The effect of a blurred image on the retina is that the eye attempts to rectify the situation by elongating to obtaina clearer focus
Supports the concept that axial elongation is the default growth mechanism
What refractive error can forced frontal field, forced lateral field, and form deprivation lead to?
Form deprivation - myopia
Forced lateral field - hyperopia
Forced frontal field - mostly myopia