Anatomy, Biochemistry, Physiology, Embryology and Development Flashcards
index of refraction of lens
1.4 centrally, 1.36 peripherally
average nonaccommodative power of lens
15-20 D
size of lens at birth? adult?
birth: 6.4mm equatorially and 3.5mm A-P
adult: 9mm equatorially and 5mm A-P
refractive changes in lens due to age?
decreasing refractive index, increased relative thickness of cortes, increasingly curved shape, and overall increased refractive power
what substance predominantly makes up lens capsule
type IV collagen
thinnest portion of lens capsule
posterior pole
largest lens crystalline? most abundant? smallest?
largest: alpha
most abundat: beta
smallest: gamma
increase or decrease in water insoluble lens proteins with age?
increase
rate limiting step in glucose metabolism in lens?
posphorlyation of glucose by hexokinase into glucose-6-phosphate (G6P)
% glucose metabolism by glycolysis? by TCA cycle? %ATP produced aerobically?
78%. 3% (low oxygen tension in lens), but due to high efficiency still produces 25% of ATP
percentage of G6P metabolized in lens by HMP shunt pathway? more or less than other tissues?
5%, which is proportionally higher than other tissues
metabolic pathway responsible for diabetic cataract?
sorbitol
affect of hyperbaric oxygen on lens?
nuclear cataract formation
relative proportions of sodium, potassium, water, chloride, and amino acids in lens
potassium and amino acids high
sodium, chloride, and water low (due to Na+/K+ pump)
embryologic origin of lens
surface ectoderm
name the first three steps of lens development in order
lens placode, lens pit, lens vesicle
orientation of Y sutures in lens?
upright Y anteriorly, inverted Y posteriorly
where do zonules originate?
secreted by ciliary epithelium
Laterality, relative commonality, and associated syndromes with anterior and posterior lenticonus
Anterior: bilateral, less common, Alport syndrome
Posterior: unilateral, more common, Lowe syndrome
most common location of Mittendorf dot
inferonasal
when does the lens vesicle normally separate from the surface ectoderm
33 weeks gestation
Microspherophakia:
- refractive state
- stubby fingers, small stature, reduce joint mobility (and inheritance)
- feared complication
- medications contraindicated in (3)
- medical and procedural treatment of (3)
- highly myopic
- Weill-Marchesani, AR
- pupillary block glaucoma
- miotics (increase pupillary block)
- cycloplegics (decrease A-P lens diameter) + LPI
Aniridia:
- laterality
- % sporadic
- associated gene
- associated findings
- workup for sporadic?
- almost always bilateral
- 1/3 sporadic
- PAX6
- epitheliopathy from decreased limbal stem cells, angle closure glaucoma, optic nerve and foveal hypolasia
- abdominal u/s to eval for Wilms tumor (WAGR = Wilms tumor, aniridia, GU anomalies, mental retardation)
basic causes of congenital cataracts and relative frequency
1/3 isolated inherited trait, 1/3 associated with systemic syndromes, 1/3 unknown
