Iris and Ciliary Body Development

Question 1

Iris development tissue origin

Answer 1

blood vessels and blood elements - MESODERMAL MESENCHYME

melanocytes and connective tissue associated with anterior border layer and iris stroma - NEURAL CREST MESENCHYME

anterior and posterior iris epithelium and smooth muscles of iris (dilator and sphincter) - NEURAL ECTODERM

Question 2

Development of Iris stroma anterior leaf

Answer 2

3rd wave of neural crest mesenchyme (6-8 wks)

vessels vascularize anterior lens - anterior tunica vasculose lentis -
iridopupillary membrane

central atrophies to form pupil

anterior leaf forms part of the anterior border layer and anterior iris stroma

Question 3

Development of Iris stroma posterior leaf

Answer 3

mesenchyme - 4th wave grows forward with the growth of the optic cup (10th wk)

forms posterior stroma and part of anterior border layer in adult

cells in this layer will differentiate and proliferate to become fibroblasts and melanocytes for posterior stroma and anterior border layer

Question 4

melanogenesis

Answer 4

melanosome mature at birth

chromatophores develop postnatally

pigmentation in anterior border layer is insignificant

if stroma has scant collagen fibril content and is thin, allows pigment epithelium to peek through and brownish color noticeable

blue irides have transparent anterior border layer allowing interference or double refraction in region of stromal colagen

Question 5

Iris in newborns

Answer 5

surface of iris is flat

stroma is thin and delicate

collagen formation enhanced late in pregnancy and after birth

crypts of fuchs are formed after birth

Question 6

formation of ciliary body and iris vasculature

Answer 6

1. 2 months: MAC forming
   - long post. ciliary arter
   - arterior ciliary arter
2. 3 month:
   - long post. cil arterie all reached ciliary body
   - all anterior ciliaries formed
   - major circle producing
   - hyaloid at peak
3. 4th month:
   - hyaloid begins to regress
   - replace annularvessel
4. 6th month:
   - long post ciliary artery extend forward in posterior leaf and anastomose with anterior ciliary artery to form the major circle of the iris -> replace annular system

Question 7

Iris epithelium formation

Answer 7

• tip of optic cup grows forward and grows behind iridopupillary membrane
• posterior epithelium is continuous with the nonpigmented epithelium of ciliary body and sensory retina
• anterior epithelium posteriorly this layer is continuous with the PE of the ciliary body and RPE
• sphincter and dilator arise from anterior epithelium or myoepithlium
• both muscles differentiate directly from neuroectoderm

Question 8

Sphincter development

Answer 8

13-14 weeks -anterior iris epithelial cells loose melanin, develop intracytoplasmic microfilaments (actin) and dense bodies and deposit a basal lamina

7 months - gap jxns from circumferential muscle bands form

8 month - sphincter free

runs circumferentially

Question 9

dilator development

Answer 9

6 months basal surface of anterior epithelium forms extensions

continues development after birth up to 5th month postnatally

fibers run radially

Question 10

pupil formation (pupillary membrane atrophy)

Answer 10

last of iris to appear

epithelium has not grown to cover lens to create epithelium free zone

site of future pupil

6th month - circulation to central blood vessels of ATVL ceases

atrophy begins

programmed cell death and phagocytosis by macrophages are involved in regression of pupillary membrane

atrophy is back to the future collarette or minor circle of the iris

dysfxn of any of these processes may play a role in the persistence of the pupllary membrane

happens 5-7 month

Question 11

persistent pupillary membrane

Answer 11

incomplete atrophy of pupillary membrane or tissue hyperplasia

few strands or partial blockage of the aperture

Question 12

epicapsular stars

Answer 12

renmants of the ATVL

deposits of the anterior capsule of the lens

does not affect acuity

can have few upper photo or many lower photo

Question 13

postnatal development

Answer 13

dilator is not fully developed until 5th month

iris acquires color during 5-6 month postnatally
-accumulation of melanin in stroma and anterior border layer

crypts of fuchs - fevelop postnatally as result of atrophy of anterior border layer

Question 14

Iris pigmentation and iris coloration development

Answer 14

during develpment posterior iris is largely amelanotic and it is continuous with the NPE of ciliary body and sensory retina

4th month: intracytoplasmic melanin increases intitally near pupil and progresses

thickness of stroma and degree of melanogenesis are determining factors of eye color at birth

brown irides later in life are result of heavily pigmented melanocytes within stroma

determined usually by 5-6 months postnatally

Question 15

aniridia

Answer 15

AKA iris hypoplasia

• malformation or hypoplasia of outflow system
• anterior and posterior cataracts
• may have lens dislocation
• optic nerve may be hypoplastic
• pax6 gene involved in differentiation of neuroepithelium

segmented defects from unsynchronized or failed growth of the optic cup rim

rare but autosomal dominant, bilateral
-defect associated with pax-6 gene

caused by: rim of optic cup fails to proliferate over anterior surface of lens
-just a stump of iris with stroma and abnormal pigment epithelium at edge of lens

Question 16

anridia clinical presentation

Answer 16

poor vision (20/200 or less)
-foveal hypoplasia

nystagmus

strabismus

photophobia

glaucoma

cataract

ectopic pentis

corneal abnormalities

optic nerve hypoplasia

Question 17

aniridia and glaucoma

Answer 17

glaucoma present in 50-70% aniridia patients

filtration area covered by stump of iris

glaucoma usually developed later in childhood or even into second decade of life