Lectures 11 Flashcards
Types of Coloboma
Retinal Coloboma
Macular Coloboma
Optic Nerve Coloboma
Coloboma
Defect - a hole in one of the structures of the eye, such as the iris, retina, choroid, or optic disc
Present from birth
Closure of the optic fissure
day 33 of gestation
Allows for pressurization of the globe
Embryonic fissure development
Develops from eccentric invagination of the optic vesicle leaving a gap INFERONASALLY
This gap allows the hyaloid artery to access the inner eye and is crucial for continued ocular development
Closure of the embryonic fissure
Begins at the equator and then proceeds anteriorly and posteriorly
Failure of closure or incomplete closure of the embryonic fissure
Results in coloboma of the cornea, iris, ciliary body, choroid, retina and/or optic nerve
Choroidal fissure
located on the undersurface of the optic stalk
Permits access into the interior of the developing eye for the precursors of the hyaloid artery and vein
Coloboma of the Eyelids
Palpebral Coloomas
Characterized by a small notch in the superior eyelid, but the defect may involve almost the entire lid
Uncommon
Result from local developmental disturbances in the formation/growth of the eyelids
Secondary symptoms: drying, ulceration of the cornea
Lens Coloboma
Due to a defective or absent development of the zonules in any segment that causes flattening of the equator of the lens
Due to a lack of tension on the lens capsule and subsequent contraction and notching in that region
Misnomer: no loss of lens tissue; actually effect of coloboma of zonules and/or ciliary body
Iris Coloboma
Defect in the inferior sector of the iris or a notch in the pupillary margin, giving the pupil a KEYHOLE appearance
Frequently hereditary (autosomal dominant characteristic)
Retinochoroidal Coloboma
Characterized by a localized gap in the retina and choroid, usually inferior to the optic disc
Usually bilateral
Does not cause symptoms
Optic Nerve Coloboma
Results from an incomplete closure of the embryonic fissure
Can either be unilateral or bilateral
Often familial
Appearance: white, bowl-shaped excavation on the inferior optic nerve head
- optic disc enlargement
- inferior neuroretinal rim is thin/absent
- superior neuroretinal rim is relatively normal
May involve the choroid and retina
Iris and ciliary colobomas may also be present
Cyclopia
Rare anomaly
The eyes are partially or completely fused, forming a single median eye enclosed in a single orbit
(single midline eye)
Cyclopia and Synophthalmia are associated with other craniocerebral defects - incompatible with life
Synophthalmia
Fusion of the eyes
Microphthalmia
Congenital microphthalmia - heterogenous group of eye defects
-autosomal dominant, autosomal recessive, or x-linked
Most cases - caused by infectious agent (rubella, toxoplasma gondii, herpes simplex virus)
May be very small and associated with other ocular defects, or may be normal-appearing rudimentary eye
Affected side is under developed, orbit is small
- arrested development of the eye before/shortly after the optic vesicle has formed in the fourth week
- lens does not form
Anophthalmia
Unilateral or bilateral
Absence of the eye (RARE)
Eyelids form, but no eyeball develops
Formation of the orbit relies on stimulation from the developing eye, so orbit defects are always present
Usually accompanied by other severe craniocerebral defects
Congenital Ptosis of Eyelid
Drooping of the superior eyelids at birth (common)
Blepharoptosis may result from failure of normal development of the levator palpebrae superioris muscle
Autosomal dominant
Vision can be affected if the eyelid margin completely or partially occludes pupil - early surgical correction necessary
If ptosis is associated with the inability to move the eyeball superiorly…
there is also failure of the superior rectus muscle of the eyeball to develop normally
Congenital Aniridia
Rare anomaly
Lack of iris tissue or almost complete absence of the iris
Results from an arrest of the development at the rim of the optic cup during the 8th week
May be associated with glaucoma, cataracts, and other eye abnormalities
May be familial (dominant) or sporadic
Mutation of the Pax6 gene results in aniridia
Congenital Aphakia
Absence of the lens is extremely rare and results from failure of the LENS PLACODE to form during the FOURTH WEEK
May also result from failure of lens induction by the OPTIC VESICLE
Lens placode formation
4th week of gestation
Congenital Cataracts
lens = opaque with frequent grayish-white appearance
without treatment, blindness results
Many are inherited dominantly
Some are caused by teratogenic agents
- rubella
- physical agents (radiation)
- enzymatic deficiency - congenital galactosemia
Lens vulnerability to Rubella Virus
4th-7th week of gestation when primary lens fibers are forming
Cataracts from congenital galactosemia
Enzyme deficiency cause
Cataracts develop as early as the second week after birth
Because of the enzyme deficiency, large amounts of galactose from milk accumulate in the infants blood and tissues, causing injury to the lens and resulting in Cataract formation
Congenital Glaucoma
Usually results from abnormal development of the drainage mechanism of the aqueous humor during the fetal period
Intraocular tension rises because of an imbalance between the production of aqueous humor and its outflow
-this imbalance may result from abnormal development of the scleral venous sinus
Genetically heterogeneous (many different genotypes)
May result from Rubella infection during early pregnancy
Mutations in the CYP1B1 gene are associated with approximately 65% of cases of congenital glaucoma
Mutations in the CYP1B1 gene
Associated with ~65% of cases of congenital glaucoma
Persistent Hyperplastic Primary Vitreous
The distal part of the hyaloid artery normally degenerates as its proximal part becomes the central artery of the retina
-PHPV = distal part of the hyaloid persisting
May appear freely moving, nonfunctional vessel or worm-like projecting from the optic disc
Sometimes appears as a fine strand traversing the vitreous body
Unusual cases: the entire distal part of the artery persists and extends from the optic disc through the vitreous body to the lens
-microphthalmic eye
Most unilateral and non-hereditary
Bilateral PHPV may follow autosomal recessive or autosomal dominant inheritance
Causes/association of bilateral PHPV
Trisomy 13 (Patau syndrome)
Autosomal dominant
Autosomal recessive
Persistent Tunica Vasculosa Lentis
Congenital ocular anomolay
Form of PHPV (developmental disorder of the vitreous)
Usually unilateral and first noticed in the neonatal period
May be associated with microphthalmos, cataracts, and increased IOP
Elongated ciliary processes are visible through the dilated pupil
Confirmed by USG B-scan in presence of a cataract
Persistent Pupillary Membrane
Remnants of pupillary membrane
May persist as web-like strands of connective tissue or vascular arcades over the pupil in neonates, especially in premature infants
Seldom interferes in vision
VERY RARELY: entire pupillary membrane persists -> congenital atresia of the pupil
Pupillary Membrane
Covers the anterior surface of the lens during the embryonic period and most of the fetal period
Epicapsular Stars
Tiny, stellate, star-shaped pigmented opacities on the anterior lens capsule
Unilateral or bilateral
Remnants of the Tunica Vasculosa Lentis
a vascular network that surrounds the lens during embryogenesis
Epicapsular stars & PPM
Bermeister Papilla
Names after Austrian ophthalmologist O. Bergmeister (1845-1918)
At birth, the hyaloid artery regresses, and is normally completely regressed by the time of eyelid opening
Bergmeister’s papilla is a remnant of the hyaloid artery fibrous sheath (a small tuft of fibrous tissue)
Arises from the center fo the optic disc
Frequently observed as an incidental clinical finding
Mittendorf’s Dot
A small, circular opacity on the posterior lens capsule
Classically nasal in location
Smal gray or white opacity
Represents the anterior attachment of the hyaloid artery
Detachment of the Retina
Occurs when the inner and outer layers of the optic cup fail to fuse during the fetal period to form the retina
Occurs in conjunction with other syndromes (Down’s and Marfan)
Separation of neural and pigment layers of the retina (partial or complete)
May result from unequal rates of growth of the 2 retinal layers
Secondary detachments: occur in association with other defects of the eye/head or trauma
Ocular Albinism
Variance in melanocytes that derive their pigment from neural crest
Melanin production is gene regulated
Melanocytes that are neuroectodermal in derivation (retinal pigment, iris, CB) are densely pigmented in all races
Sensory retina development is affected (absent pigment)
Macula underdeveloped, fovea may be absent
Number of rods may be decreased
Abnormal optic nerve projection to LGN (more crossed fibers than normal) producing binocular problems
Retinopathy of Prematurity
ROP
Potentially blinding eye disorder that primarily affects premature infants weighing 2 3/4 lbs (1250 grams) or less that are born before 31 weeks gestation
Premature infants who are exposed to a high concentration of oxygen (oxygen chamer)
Complications: neovascular invasion of vitreous, vitreoretinal adhesions, hemorrhage, retinal detachment
Occurs in 4 stages
Papilledema
Edema of the Optic Disc
Increase in CSF pressure slows venous return from retina, causing fluid accumulation of the optic disc
Occurs because the retinal vessels are covered with pia mater and lie in the extension of the subarachnoid space that surrounds the optic nerve
Tilted ONH
Common in high myopia
ON typically exits sclera at 90˚ angle
Tilted: occurs when nerve exits eye at oblique angle
Typically bilateral in which superiortemporal disc is raised, simulating disc swelling, which the inferiornasal disc is flat or depressed
Thinning of RPE and choroid in the inferior nasal quadrant
Optic Nerve Hypoplasia
ONH appears abnormally small due to a low number of axons
The disc may appear gray or pale and is surrounded by a light-colored peripillary hallo
At the normal junction between the sclera and lamina cribosa, there is another change in pigmentation, a “double ring sign,” associated with the hypoplasia
Aplasia of the ONH
RARE, congenital developmental anomaly, comprising of absence of ON, central retinal vessels and ganglion cells
Usually accompanied by other central nervous system anomalies, micropthalmous
Often unilateral
