Fundamentals and Principles of Ophthalmology Flashcards
What is the volume of the adult orbit?
Slightly less than 30cc
What is the average orbital height and width at the entrance, respectively?
35mm and 45mm
What is the depth of the orbit from the orbital entrance to the orbital apex?
40-45mm
What seven bones make up the bony orbit?
Frontal, zygomatic, maxillary, ethmoidal, sphenoid, lacrimal, palatine
These four bones make up the medial wall of the orbit.
Frontal process of maxillary bone, lacrimal bone, orbital plate of ethmoid bone, and lesser wing of sphenoid bone
These three bones make up the orbital floor.
Maxillary, palatine, and orbital plate of the zygomatic bone
This is a small elevation of the orbital margin of the zygomatic bone that lies ~11mm below the frontozygomatic suture. It is the site of attachment for: ligament of lateral rectus, suspensory ligament of the eyeball (Lockwood suspensory ligament), aponeurosis of levator palpebrae superioris, and the Whitnall ligament.
Whitnall tubercle (lateral orbital tubercle)
The superior orbital fissure transmits these four structures.
Lacrimal nerve (CN V1), frontal nerve (V1), CN IV (trochlear), superior ophthalmic vein
These are the three roots that are received by the ciliary ganglion (located about 1cm in front of the annulus of Zinn).
Nasociliary branch of V1 (sensory from cornea, iris, ciliary body), inferior division of CN III (inferior oblique, parasympathetic to iris), sympathetics (do not synapse; innervates blood vessels and dilator muscle of pupil)
These are the lengths of insertions of the medial, inferior, lateral, and superior recti, respectively, that form the spiral of Tillaux.
5.5, 6.5, 6.9, and 7.7mm
This consists of superior and inferior orbital tendons and is the origin of the four rectus muscles.
Annulus of Zinn
This muscle arises from the lesser wing of the sphenoid bone, at the apex of the orbit, just superior to the annulus of Zinn.
Levator palpebrae superioris
This muscle originates from the periosteum of the body of the sphenoid bone, above and medial to the optic foramen.
Superior oblique
This muscle originates anteriorly, from a shallow depression in the orbital plate of the maxillary bone, at the anteromedial corner of the orbital floor near the lacrimal fossa.
Inferior oblique
Innervation of the lateral rectus.
CN VI (abducens nerve)
The upper division of CN3 (oculomotor) innervates these muscles.
Levator palpebrae superioris and superior rectus
The lower division of CN3 (oculomotor) innervates these muscles.
Medial rectus, inferior rectus, and inferior oblique
This type of muscle fiber is unique to extraocular muscles. They are smaller than twitch-type fibers and contract slowly and smoothly. They tend to be more superficial (near the orbital wall) and are innervated by multiple grapelike nerve endings (en grappe). Theya re useful for smooth pursuit.
Tonic-type muscle fibers
These muscle fibers are similar to skeletal muscle fibers. The are larger and located deeper in the muscle. They contract rapidly and have platelike nerve endings (en plaque). They aid in rapid saccadic movements of the eye.
Twitch-type muscle fibers
How much can the upper eyelid be raised by the action of the levator palpebrae superioris muscle alone?
15mm
How much can the upper eyelid be raised by the frontalis muscle?
2mm
The superior eyelid fold is present near the upper border of the tarsus, where this establishes its first insertional attachments. Since few attachments are present in many Asian individuals, the superior eyelid fold is minimal or absent.
Levator aponeurosis
The delicate gray line (or intermarginal sulcus) corresponds histologically to the most superficial portion of this muscle, as well as to the avascular plane of the eyelid. Anterior to this line, the eyelashes (cilia) arise, and posterior to this line are the openings of the tarsal (or meibomian) glands.
Orbicularis oculi (muscle of Riolan)
These are modified sebaceous glands associated with the cilia (eyelashes).
Glands of Zeis
These are apocrine sweat glands of the skin that are around the margins of the eyelashes.
Glands of Moll
This part of the orbicularis oculi muscle acts as a sphincter and functions solely as a voluntary muscle. It inserts in a complex way into the medial canthal tendon and other portions of the orbital rim and the corrugator supercilii muscle.
Orbital part
This part of the orbicularis oculi muscle functions both voluntarily and involuntarily in spontaneous and reflex blinking.
Palpebral part
This is a thin sheet of connective tissue that encircles the orbit as an extension of the periosteum of the orbital floor and roof.
Orbital septum
The levator palpebrae superioris changes near the Whitnall ligament and divides anterior into the aponeurosis and posteriorly into this. It is sympathetically innervated.
Superior tarsal (Muller) muscle
These are modified holocrine sebaceous glands that are oriented vertically in parallel rows through the tarsus. There are 30-40 orifices in the upper eyelid and 20-30 in the lower lid.
Tarsal (meibomian) glands
This is misdirection in the orientation of the eyelashes.
Trichiasis
This is aberrant growth of eyelashes through the orificies of the meibomian glands.
Distichiasis
The medial group of lymphatics in the eyelids drain into these nodes.
Submandibular lymph nodes
The lateral group of lymphatics in the eyelids drain into these nodes.
Superficial preauricular lymph nodes
This is a small, fleshy, ovoid structure attached to the inferomedial side of the plica semilunaris. It is a piece of modified skin that contains sebaceous glands and fine, colorless hairs.
Caruncle
This is a narrow, highly vascular, crescent-shaped fold of conjunctiva lateral and partly under the caruncle. It is a vestigial structure analogous to the nictitating membrane (3rd eyelid) of dogs and other animals.
Plica semilunaris
These cells line the lumen of the lacrimal gland
Acinar cells
These cells surround the parenchyma of the lacrimal gland and are covered by a basement membrane.
Myoepithelial cells
These are two accessory lacrimal glands that are located at the proximal lid borders. They are cytologically identical to the main lacrimal gland and receive similar innervation (secretomotor cholinergic, VIP, sympathetic, and sensory via CN V1 lacrimal nerve)
Accessory lacrimal glands of Krause and Wolfring
This is the approximate diameter of the lacrimal puncta
0.3mm
The inferior and superior puncta are about how far from the medial canthus, respectively?
6.5mm, 6.0mm
This is a mucous membrane consisting of nonkeratinizing squamous epithelium with numerous goblet cells and a thin, richly vascularized substantia propria containing lymphatic vessels, plasma cells, macrophages, and mast cells. In places, there are collections of T and B lymphocytes (they corresond with MALT). It is divided into 3 geographic areas: palpebral, forniceal, and bulbar.
Conjunctiva
This is an envelope of elastic connective tissue that fuses posteriorly with the optic nerve sheath and anteriorly with the thin intermuscular septum (3mm from the limbus). It is the cavity within which the globe moves.
Tenon capsule (fascia bulbi)
This is a fusion of the sheath of the inferior rectus, inferior tarsal muscle, and the check ligaments of the medial and lateral recti. It provides support for the globe and the anteroinferior orbit.
Lockwood ligament
These arteries originate from the ophthalmic artery and supply the whole uveal tract, the cilioretinal arteries, the sclera, the margin of the cornea, and the adjacent conjunctiva. Occlusion (as in giant cell arteritis) can have profound consequences (such as anterior ischemic optic neuropathy). Within the eye, they form the intramuscular circle of the iris, from which branches supply the major arterial circle (which is usually discontinuous). This circle lies within the apex of the ciliary muscle, which it supplies together with the iris.
Posterior ciliary arteries
These arteries arise from the ophthalmic artery and usually supply (in pairs) the superior, medial, and inferior rectus muscles.
Anterior ciliary arteries
These vessels drain the venous system of the choroid, ciliary body, and iris. They exit 14-25mm from the limbus between the rectus muscles.
Vortex veins
These are the radius of the curvature of the cornea and that of the sclera, respectively, making the shape of the globe an oblate spheroid.
8mm, 12mm
How deep is the anterior chamber, and what is its average volume?
3mm, 200 microliters
What is the average volume of the posterior chamber?
60 microliters
What is the volume of the vitreous cavity?
5-6ml
What is the volume of the average adult eye?
6.5-7.0ml
This is the cornea’s posterior landmark, which is the termination of the Descemet membrane.
Schwalbe line
A persistent membrane over this structure in infants leads to excessive tearing and discharge.
Valve of Hasner
What are the three layers of the precorneal tear film, and where are each predominantly produced?
Superficial oily layer (meibomian glands), middle aqueous layer (lacrimal glands), deep mucin layer (conjunctival goblet cells)
The air-tear film interface at the surface of the cornea forms a lens of approximately this power. It is the main refractive element of the eye.
+43D
This is a tough layer of the cornea that consists of randomly dispersed collagen fibrils. It is a modified region of the anterior stroma that is 8-12 micrometers thick. It is not restored after injury but rather replaced by scar tissue.
Bowman layer (membrane)
This is the basal lamina of the corneal endothelium that is PAS positive. It is 3-5 micrometers thick at birth and increases to 10-12 micrometers at adulthood. It is rich in type IV collagen.
Descemet membrane
These are peripheral excrescences of the Descemet membrane that are common especially among elderly people.
Hassall-Henle warts
There are central excrescences in the Descemet membrane that can appear with increasing age or certain diseases (such as Fuch’s corneal dystrophy)
Cornea guttae (guttata)
The active transport of ions by these hexagonal cells leads to the transfer of water from the corneal stroma and the maintenance of stroma deturgescence and transparency. Mitosis is rare in humans, and the overall number decrease with age.
Corneal endothelial cells
Where is the sclera thinnest and thickest?
Thinnest (0.3mm): just behind the insertions of the rectus muscles. Thickest (1.0mm): posterior pole around optic nerve head.
What is the most common site of scleral rupture following traumatic injury?
Superonasal quadrant near the limbus
These five structures are included in the limbus, or transition zone between the peripheral cornea and the anterior sclera.
Conjunctiva/limbal palisades, tenon capsule, episclera, corneoscleral stroma, aqueous outflow apparatus
The anterior chamber angle, which lies at the junction of the cornea and the iris, consists of these five structures.
Schwalbe line, Schlemm canal/trabecular meshwork, scleral spur, anterior border of the ciliary body, iris
This is a nontrabecular drainage pathway across the ciliary body into the supraciliary space. It may be influenced by age, and it accounts for up to 50% of aqueous outflow in young people.
Uveoscleral Pathway
This receives the insertion of the longitudinal ciliary muscle, and contraction opens up the trabecular spaces. Contractile cells are found within this structure, as well as mechanoreceptors which receive sensory innervation.
Scleral spur
These are the three different nerve pathways (and five different nevre fibers) that innervate the myofibroblast-like scleral spur cells and that cause an increase in outflow from the trabecular meshwork.
Sympathetic, sensory, pterygopalatine nerve pathways (neuropeptide Y, substance P, CGRP, VIP, NO) (**NO cholinergic fibers)
This is a circular spongework of connective tissue lined by trabeculocytes, with contractile and phagocytic properties. It is roughly triangular in cross section, with the apex at the Schwalbe line and base formed by the scleral spur and ciliary body.
Trabecular meshwork
This is a circular tube that closely resembles a lymphatic vessel, formed by a continuous monolayer of nonfenestrated endothelium and a thin connective tissue wall. There are giant vacuoles along the internal canal wall, and their size and number are increased by a rise in IOP which may contribute to the pressure-dependent outflow of the aqueous humor.
Schelmm canal
This is the thickest portion of the iris stroma where anastomoses occur between the arterial and venous arcades to form the minor vascular circle of the iris.
The collarette
This term refers to an outfolding over the pupil of the iris pigment epithelium. It is a misnomer because the IPE is derived from neural ectoderm (not neural crest) and therefore is not considered part of the uvea.
Ectropion uveae
What is the pathway of the first order sympathetic neurons to the dilator muscle?
Begin in ipsilateral posterolateral hypothalamus, pass thru brainstem, synapse in the IML of the spinal cord (mainly T1).
What is the pathway of the second order sympathetic neurons to the dilator muscle?
Begin in the IML (mainly T1), exit spinal cord, pass over pulmonary apex and thru stellate ganglion, synapses in the superior cervical ganglion.
What is the pathway of the third order sympathetic neurons to the dilator muscle?
Begin in the superior cervical ganglion, joins internal carotid plexus, enters cavernous sinus, travels with CN V1 to orbit and to dilator muscle.
What is the pathway of the presynpatic parasympathetic neurons to the iris sphincter muscle?
Begin in the Edinger-Westphal subnucleus of CN3, follow inferior division of CN3 into cavernous sinus and to inferior oblique muscle, synapse in ciliary ganglion.
What is the pathway of the postsynpatic parasympathetic neurons to the iris sphincter muscle?
Begin in the ciliary ganglion, travel with short ciliary nerves to the iris sphincter. (unusual in that they are myelinated)
This is a relatively avascular, smooth, pigmented zone of the ciliary body that is 4mm wide and extends from the ora serrata to the ciliary processes. It is the safest posterior surgical approach to the vitreous cavity (3-4mm from the corneal limbus).
Pars plana
This is a PAS-positive lamina resulting from the fusion of the basal laminae of the RPE and the choriocapillaris of the choroid, extending from the optic disc to the ora serrata. It consists of a series of connective tissue sheets that are highly permeable to small molecules (such as fluoroscein). Defects may appear spontaneously in myopia/pseudoxanthoma elasticum, or they may result from trauma or inflammation.
Bruch membrane
This is a continuous layer of large capillaries lying in a single plane beneath the RPE. They contain multiple fenestrations.
Choriocapillaris
How much focusing power does the lens contribute in the average adult eye?
+20.00D
This is the lens basal lamina, which is a product of lens epithelium, that is rich in type IV collagen.
Lens campsule
What is the thickness of the anterior and posterior lens capsule in the adult lens, respectively?
Anterior: 15.5 micrometers; posterior: 2.8 micrometers
This is the orientation of the Y-shaped suture anteriorly and posteriorly in the lens, formed by interdigitation of the anterior and posterior tips of the spindle-shaped fibers.
Anterior: Y-shaped; posterior: inverted Y-shaped
The lens is held in place by these. They originate from the basal laminae of the nonpigmented epithelium of the pars plana and plicata of the ciliary body. Mutations in the fibrillin gene lead to weakening of these and subluxation of the lens.
Zonular fibers (suspensory ligaments)
These are the 10 layers of the neurosensory retina, from inner to outer retina
ILM, NFL, GCL, IPL, INL, middle limiting membrane, OPL, ONL, ELM, rod/cone inner and outer segments
This is a monolayer of hexagonal (cuboidal) cells that extends anteriorly from the optic disc to the ora serrata. It has many functions, including: vitamin A metabolism, maintenance of the outer BRB, phagocytosis of photoreceptor outer segments, light absorption, heat exchange, formation of basal lamina of Bruch membrane, production of mucopolysaccharide matrix surrounding outer segments, and active transport of materials.
Retinal pigment epithelium (RPE)
These are “wear-and-tear” pigments that probably arises from the discs of photoreceptor out segments and represent residual bodies arising from phagosomal activity. These are less electron dense than melanosomes, increase with age, and are responsible for the signal observed with fundus autofluorescence.
Lipofuscin granules
These are glial cells that extend vertically from the ELM inward to the ILM, with their nucleus in the INL. The provide structural support and nutrition to the retina and are crucial to normal physiology.
Muller cells
The inner portion of the retina is perfused by branches of this artery.
Central retinal artery (cilioretinal artery from the ciliary circulation also present in 18-32% of eyes)
This is not a true membrane; it is formed by the attachment sites of adjacent photoreceptors and Muller cells and is highly fenestrated. It is the outermost layer of the neurosensory retina.
External limiting membrane (ELM)
This term refers to the outer plexiform layer (OPL, composed of interconnections between photoreceptor synaptic bodies and horizontal and bipolar cells) in the macular region, where it is thicker and contains more fibers because the axons of the rods and cones become longer and more oblique as they deviate from the fovea.
Henle fiber layer
This region of the neurosensory retina contains nuclei of bipolar, Muller, horizontal, and amacrine cells.
Inner nuclear layer (INL)
This is not a true membrane; it is formed by the footplates of Muller cells and attachments to the basal lamina (smooth on the vitreal side but undulating on the retinal side where it follows the contour of the Muller cells).
Internal limiting membrane (ILM)
Cells and their processes of the neurosensory retina are oriented perpendicular to the plane of the RPE. Because of this, blood or exudates tend to form round blots in the _ layers (where small capillaries are found) and linear or flame-shaped patterns in the _ layer. As a result, radial or star-shaped patterns may arise when these extracellular spaces are filled with serum and exudate.
Outer layers; nerve fiber layer
These are two major carotenoid pigments located chiefly in the Henle fiber layer. Their proportions vary with distance from the fovea, corresponding to the rod-to-cone ratio. The former is more concentrated in cone-dense areas; the latter is more concentrated in rod-dense areas of the retina.
Zeaxanthin, lutein
What is the approximate diameter of the fovea?
1.5mm (comparable to the optic nerve head)
This is where the GCL, INL, and OPL are thickest. It is 0.5mm wide and surrounds the fovea.
Parafovea
This is the most peripheral region of the macula that is about 1.5mm wide.
Perifovea
This is the boundary between the retina and the pars plana. It is temporally smooth and serrated nasally, and retinal blood vessels end in loops prior to reaching this boundary. It is a watershed zone between the anterior and posterior vascular systems.
Ora serrata
This occupies 4/5 of the volume of the globe and consists of 99% water (although it is twice as viscous as water, mainly due to hyaluronic acid). It becomes more fluid with age and frequently separates from the inner retina.
Vitreous
This is an S-shaped channel that forms due to the regression of the hyaloid vasculature during embryonic development. It passes sinuously from a point slightly nasal to the posterior pole of the lens to the margin of the optic nerve head.
Cloquet canal
This is a point slightly nasal to the posterior pole of the lens present in some individuals that is a remnant of the fetal hyaloid vasculature.
Mittendorf dot
These are remnants of the fetal hyaloid vasculature that can be observed clinically on the optic nerve head in the adult.
Vascular loops and Bergmeister papilla
This comprises ~10 connective tissue plates integrated with the sclera and whose pores transmit axon bundles of CN2. It contains type 1 and 3 collagens, elastin, laminin, and fibronectin. Functions include: scaffold for optic nerve axons, point of fixation for the CRA and CRV, and reinforcement of the posterior globe.
Lamina cribrosa
This is the innermost layer of the optic nerve sheath. It is a vascular connective tissue coat covered with meningothelial cells that sends numerous septa into the optic nerve, dividing its axons into bundles.
Pia mater
This usually occurs from blunt trauma over the eyebrow that can transmit the force of the injury to the intracanalicular region, causing shearing and interruption of blood supply to the optic nerve. It can also cause optic nerve edema and compartment syndrome.
Indirect traumatic optic neuropathy
After passing through the optic canal, the optic nerve passes posteriorly over the carvernous sinus to joint this structure.
Optic chiasm
The optic chiasm divides into the left and right optic tracts, which end in these structures. They are the synpatic zone for higher visual projections.
Lateral geniculate bodies
These arise from the lateral geniculate bodies, and they send signals to the primary visual cortex. Damage to this structure in the anterior temporal lobe gives rise to a wedge-shaped, upper homonymous “pie in the sky” visual field defect.
Geniculocalcarine pathways (optic radiations)
What supplies blood to the retrolaminar optic nerve?
Pial vessels and short posterior cilial vessels, with some help from the CRA and recurrent choroidal arteries
What supplies blood to the laminar optic nerve?
Short posterior ciliary arteries or branches of the arterial circle of Haller and Zinn (circle of Zinn-Haller)
What supplies blood to the prelaminar optic nerve?
Short posterior ciliary arteries and recurrent choroidal arteries; NFL supplied by the CRA
What supplies blood to the intraorbital region of the optic nerve?
Proximally: pial vascular network and branches of the ophthalmic artery; distally: intraneural branches of the CRA; most anteriorly: short posterior ciliary arteries and occasional peripapillary choroidal arteries
What supplies blood to the intracanalicular region of the optic nerve?
Branches of both the ICA and ophthalmic artery
Each of these contain ipsilateral temporal and contralateral nasal fibers from the optic nerves. Fibers (both crossed and uncrossed) from the upper retinal projections travel medially within this, and lower projections move laterally. Macular fibers adopt a dorsolateral orientation toward the lateral geniculate body.
Optic tract
These layers of the lateral geniculate body contain axons from the contralateral optic nerve (layers are numbered consecutive from below to upward).
Layers 1, 4, and 6
These layers of the lateral geniculate body contain axons from the ipsilateral optic nerve (layers are numbered consecutive from below to upward).
Layers 2, 3, and 5
The is the name of the path of the optic radiations that leave the lateral geniculate body and wind around the temporal horn of the lateral ventricle, approaching the anterior tip of the temporal lobe.
Loop of Meyer
This is the thinnest area of the human cerebral cortex. The PCA supplies blood almost exclusively. Macular function occupies the most posterior position, and the most anterior portion of the calcarine fissure is occupied by contralateral nasal retinal fibers only.
Visual cortex
This is used to explain the conjugacy of saccadic eye movement. The law proposes that conjugacy of saccades is due to innate connections in which the eye muscles responsible for each eye’s movements are innervated equally.
Hering’s law of equal innervation
This provides the parasympathetic preganglionic efferent innervation to the ciliary muscle and pupillary sphincter.
Edinger-Westphal nucleus
Describe the pathway of the light reflex (simultaneous and equal constriction of the pupils in response to illumination of one eye or the other).
AFFERENT: Retina -> optic nerve -> optic chiasm -> optic tract -> pretectal nucleus -> Edinger-Westphal nucleus (ipsilateral and contralateral); EFFERENT: bilateral CN3 -> inferior division -> ciliary ganglion -> short ciliary nerve -> ciliary sphincters
Describe the pathway of the near reflex (accommodation, pupil constriction, and convergence when attention is changed from distance to near)
Occipital association cortex -> corticofugal pathways -> pretectal area -> Edinger-Westphal nuclei, motor nuclei of medial recti, nucleus of CNVI
This cranial nerve contains the fewest fibers (~3400) but has the longest intracranial course (75mm). It runs superiorly outside of the muscle cone, so it is usually not affected by injection of retrobulbar anesthetics.
CN IV (Trochlear)
This nucleus of CN V mediates proprioception and deep sensation from the masticatory, facial, and extraocular muscles.
Mesencephalic nucleus
This nucleus of CN V lies in the pons. It receives input from ascending branches of the sensory root and serves light touch from the skin and mucous membranes.
Main sensory nucleus
This nucleus and tract of CN V extend through the medulla to C4. The nucleus receives pain and temperature afferents from the descending tract, including distributions of V1-3 (also carrying cutaneous components of CN VII, IX, and X).
Spinal nucleus and tract
This nucleus of CN V receives fibers from both cerebral hemispheres, the reticular formation, the red nucleus, the tectum, the MLF, and the mesencephalic nucleus. It supplies muscles of mastication (pterygoid, masseter, and temporalis), tensor tympani, tensor veli palatini, mylohyoid muscle, and the anterior belly of the digastric muscle.
Motor nucleus
These are the three branches of the ophthalmic division of CN V (V1).
Frontal, lacrimal, and nasociliary
The frontal nerve divides into these two nerves, which provide sensation to the medial portion of the upper eyelid and the conjunctiva, forehead, scalp, frontal sinuses, and side of the nose.
Supraorbital and supratrochlear nerves
This nerve innervates the lacrimal gland and neighboring conjunctiva and skin.
Lacrimal nerve
This nerve supplies sensation to the middle and inferior turbinates, septum, lateral nasal wall, and tip of the nose.
Nasociliary nerve
This nerve exits the skull through the foramen rotundum and passes through the infraorbital canal as the infraorbital nerve. It supplies the lower eyelid, side of the nose, upper lip, teeth, maxillary sinus, roof of the mouth, and soft palate.
CN V2 (maxillary division)
This nerve contains both sensory and motor fibers, exits the skull through the foramen ovale, and provides motor to the masticatory muscles and sensory to the mucosa and skin of the mandible, lower lip, tongue, external ear, and tympanum.
CN V3 (mandibular division)
This is the sensory root of CN VII, which contains special visceral afferent (taste from anterior two-thirds of tongue), general somatic afferent (sensation from external auditory meatus and retroauricular skin), and general visceral efferent fibers (preganglionic parasympathetic to lacrimal submaxillary, and sublingual glands).
Nervus intermedius
These are the six structures located within the cavernous sinus, which is an interconnected series of venous channels located just posterior to the orbital apex and lateral to the sphenoidal air sinus and pituitary fossa.
ICA (surrounded by sympathetic carotid plexus), CNIII, CN IV, CN VI, CN V1, and CN V2
The corneal epithelium is derived from what embryonic structure?
Surface ectoderm
The corneal stroma and endothelium is derived from what embryonic structure?
Neural crest cells
These are the five layers of the Bruch membrane.
Basement membrane of the RPE, inner collagenous zone, elastic fibers, outer collagenous zone, basement membrane of the choriocapillaris
When does lacrimal gland (reflex) tear production begin after birth?
20 or more days (newborns cry without tears)
This is a homeobox (Hox) gene that appears to be a master switch for eye developemtn. It is expressed very early in the primordial eye field, and ectopic expression leads to ectopic eyes.
PAX6 (PAired homeoboX 6)
During which week gestation do the eyelids grow over the eye?
Seven weeks
During which week gestation do the eyelids fuse, and where does fusion start?
Eight weeks, beginning along the nasal margin
This is a disorder involving progressive ptosis and paralysis of eye muscles associated with a ragged red myopathy, usually resulting from a deletion of a portion of the mitochondrial genome. They often have pigmentary retinopathy.
Chronic progressive external ophthalmoplegia
This is chronic progressive external ophthalmoplegia (CPEO) associated with heart block and severe retinitis pigmentosa with marked visual impairment.
Kearns-Sayre syndrome
This mitochondrial disease is associated with a single base change (G to A at nucleotide position 11778 in the ND-4 gene) in human mtDNA involved in the synthesis of NADH dehydrogenase. It is characterized by optic atrophy and peripapillary microangiopathy.
Leber hereditary optic neuropathy
This mitochondrial disease is associated with a single base-pair mutation at nucleotide position 8993 in the ATPase-6 gene. The phenotype occurs when the percentage of mutant mtDNA is less than 80%, whereas >95% mutated genes can cause Leigh syndrome, a severe neurodegenerative disease of infancy and early childhood.
Neuropathy, ataxia, and retinitis pigmentosa (NARP)
These are two different mitochondrial disorders that are associated with an A to G 3243 mtDNA point mutation, affecting an mt transfer RNA. Macular retinal pigment epithelial atrophy has been described with this mutation.
Mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS) and maternally inherited diabetes and deafness (MIDD)
This condition is caused by hemizygosity of the Rb locus within human chromosome band 13q14, a member of a class of genes called recessive tumor-suppressor genes.
Familial retinoblastoma
This occurs from a defect in PAX6, located at 11p13, leading to a panophthalmic disorder characterized by: subnormal VA, congenital nystagmus, strabismus, keratitis due to limbal stem cell failure, cataracts (usually anterior polar), ectopia lentis, glaucoma, optic nerve hypoplasia, foveal hypoplasia, and iris absence or severe hypoplasia.
Aniridia (short arm 11 deletion [11p13] syndrome)
This rare autosomal recessive disorder is characterized by partial aniridia, cerebellar ataxia, mental deficiency, and congenital cataracts.
Gillespie syndrome
These are the associated findings in WAGR syndrome
Wilms tumor, aniridia, genitourinary anomalies, mental retardation
This is the presentation of multiple phenotypic abnormalities produced by a single mutant gene
Pleiotropism
This occurs with higher frequency in persons of Puerto Rican ancestry. It is an autosomal recessive oculocutaneous albinism that is associated with prolonged bleeding time and abnormal platelet aggregation, leading to easy bleeding and bruising
Hermansky-Pudlak Syndrome
Three abnormal ocular findings in blue-cone monochromatism X-linked carriers
Abnormalities in cone function on ERG, psychophysical thresholds, and color vision
Retinal findings in X-linked carriers of this condition include “moth-eaten” fundus pigmentary changes (w/ areas of hypopigmentation), mottling, and pigment clumping in a striated pattern near the equator
Choroideremia
ERG findings in X-linked carriers of congenital stationary night blindness with myopia
Reductions in ERG oscillatory potentials
Ocular findings in X-linked carriers of Fabry disease
Fingerprint or whorl-like (verticillata) changes within the corneal epithelium
Ocular findings in X-liked carriers of Lowe syndrome
Scattered punctate lens opacities on SLE (nucleated cells in nucleus)
This condition presents in X-linked carriers with chocolate brown clusters of pigment prominent in the midperipheral retina; mottling of macular pigment; and iris transillumination
Ocular albinism
X-linked carriers of this condition have regional fundus pigmentary changes, “gold-dust” tapetal-like reflex, and ERG amplitude and implicit time abnormalities
X-Linked Retinitis Pigmentosa
Three primary functions of the tear film
- Provide smooth optical surface at air-cornea interface
- Serve as medium for removal of debris
- Protect the ocular surface
Four functions of the lipid layer of the tear film
- Slow evaporation
- Contribute to optical properties of tear film
- Prevent tear overflow by increasing surface tension
- Prevent damage to eyelid margin skin by tears
Six functions of aqueous layer of tear film
- Supply oxygen to corneal epithelium
- Maintain electrolyte composition over epithelium
- Antibacterial/antiviral defense
- Smooth minute irregularities of anterior corneal surface
- Wash away debris
- Modulate corneal and conjunctival epithelial cell function
This divides the main lacrimal gland into 2 anatomical parts (orbital and palpebral)
Levator aponeurosis
This accessory lacrimal gland is located in the lateral part of the upper fornix as well as the lower fornix
Glands of Krause
This accessory lacrimal gland is located variably along the proximal margin of each tarsus.
Glands of Wolfring
Four function of the mucin layer of the tear film.
- Convert K epithelium from hydrophobic to hydrophilic (essential for even distribution of tear film)
- Stabilize tear film (interacting with lipid layer to lower surface tension)
- Trap exfoliated surface cells, foreign particles, and bacteria
- Lubricate eyelids as they pass over the globe
This glucose metabolic pathway breaks down 35-65% of glucose in the corneal epithelium and endothelium, but it is not very active in the keratocytes of the stroma.
Hexose monophosphate (HMP) shunt (keratocytes lack 6-phosphogluconate dehydrogenase)
These two enzymes constitute 40-50% of soluble proteins in the corneal stroma. They are thought to contribute to the optical properties of the lens, as well as protect K cells against free radicals and oxidative damage by absorbing UVB irradiation.
Aldehyde Dehydrogenase and Transketolase
This corneal layer is about 50um thick and constitutes 5-10% of total corneal thickness. It is composed of 4-6 layers (1-2 layers of superficial squamous cells, 2-3 layers of broad wing cells, and an inner layer of columnar basal cells)
Corneal epithelium
This corneal layer is 8-12 um thick and is composed of randomly packed type I and V collagen fibers. It is secreted during embroygenesis and does not regenerate when damaged (hence the increased risk of haze after PRK but not LASIK)
Bowman Layer
This corneal layer makes up 90% of the corneal thickness. Its major component is type I collagen, which constitutes ~70% of the total dry weight of this layer. It also contains collagen types V, VI, VII, XII, and XIV
Corneal stroma
These three glycosaminoglycans are found in the corneal stroma
Keratan sulfate, chondroitin sulfate, and dermatan sulfate
This corneal layer is a specialized basement membrane that is 10-12um thick. It is comprised of an anterior banded portion and posterior non-banded portion. It is primarily composed of type IV collagen
Descemet membrane
This corneal layer is a single layer composed of polygonal cells 20um in diameter. The number of cells normally decreases with age, with a concomitant spreading and thinning of the remaining cells. It functions as a permeability barrier and as a pump to maintain the cornea in a dehydrated state. It generates the hydrostatic pressure that serves to hold free corneal flaps (eg, LASIK flaps) in place
Corneal endothelium
Normal corneal endothelial count in a young adult
3000/mm2
This is the result of infiltration of PMN leukocytes in response to severe corneal injury, inducing endothelial cells to become fibroblastic; it forms between the Descemet membrane and K endothelium, leading to significant loss of visual acuity
Retrocorneal fibrous membrane (RCFM)
Three major functions of the aqueous humor
- Nutrients (glucose and amino acids) to support structures of anterior segment
- Removes metabolic waste products (lactic acid, pyruvic acid)
- Helps maintain appropriate IOP
This secretes aqueous humor from a substrate of blood plasma
Nonpigmented ciliary epithelium
Rate of aqueous humor secretion by the ciliary epithelium into the A/C
2-3 uL/min
Orientation of epithelial layers of the ciliary body, as well as their junctions
Apex of NPE to apex of PE, tight junctions at the apical plasma membrane of the NPE (forms blood-ocular barrier in this part of the eye)
Source of oxygen to the corneal endothelium
Aqueous humor (from blood supply to ciliary body and iris; no net flux of atmospheric oxygen across cornea)
Embryological origin of the smooth muscle in the iris and ciliary body
Neuroectoderm
These play a key role in regulation of smooth muscle contractility, mediation of pain and fever, regulation of blood pressure and platelet aggregation, and other physiologic defense mechanisms (including immune and inflammatory responses)
Prostaglandins
Primary collagen of the lens capsule
Type IV collagen
Location of the germinative zone of the lens epithelium
Anterior pre-equatorial region
Location of younger lens fibers in relation to older ones
Exterior (like rings of a tree)
This is the zone or region at the lens equator that is formed by the cell nuclei as new fiber cells elongate and differentiate into mature fibers
Bow zone/region
This is a lens-fiber-specific membrane protein that likely functions as a water channel
Major intrinsic protein (MIP)
These are water-soluble proteins with high abundance in the lens with two obvious attributes: very stable (probably the longest-lived proteins in the body) and soluble under conditions of high protein concentration without forming large aggregates
Crystallins
This is the largest of the lens crystallins
alpha-Crystallin
The most abundant lens crystallin
beta-Crystallin
Primary pathway of ATP production in the crystallin lens
Anaerobic glycolysis
Rate-limiting enzyme of the glycolytic pathway
Hexokinase
Glucose metabolic pathway that is activated under conditions of oxidative stress, since it is responsible for replenishing the supply of NADPH that becomes oxidized through the increased activity of glutathione reductase under such conditions
Pentose phosphate pathway (hexose monophosphate shunt)
Condition under which a “snowflake” cataract develops (rapidly-developing, bilateral cataracts)
Poorly controlled type 1 diabetes (“sugar” cataracts)
This is caused by a deficiency of galactose-1-phosphate uridyltransferase, leading to bilateral cataracts within a few weeks of birth unless lactose is removed from the diet
Classic galactosemia
The glucose metabolic pathway responsible for diabetic cataracts
Polyol pathway (leading to increased sorbitol in the lens, which creates an osmotic gradient and draws water into the lens, swelling cells, damaging membranes, and causing cataracts)
This is a specialized connective tissue with the following functions: transparent gel that occupies the major volume of the globe and acting as a conduit for nutrients and other solutes to and from the lens
Vitreous body
Three types of collagen that comprise the vitreous collagen fibrils
Types II (major component), IX (surface of fibril), and V/XI
This is a polysaccharide (glycosaminoglycan) with a high affinity for water molecules; it occupies an extremely large volume and probably uses all of the space in the vitreous expect for that occupied by the collagen fibrils
Hyaluronan
These are two novel glycoproteins that are thought to play key roles in the structure of the collagen fibril
Opticin and VIT1
These are the two laminar structures that arise from an invagination of the embryonic optic cup that folds an ectodermal layer into apex-to-apex contact with itself, creating the subretinal space
Neurosensory retina and RPE
This is a specialized organelle of the photoreceptor cell that catches light and converts its minute amount of energy into a neural response
Outer Segment
This is a freely diffusible membrane protein in rods that is capable of responding to a single quantum of light, absorbing green light best at wavelengths of 510nm (it absorbs blue and yellow light less well and is insensitive to red light or longer wavelengths)
Rhodopsin
Three types of cones in humans
L- (long-wavelength), M- (middle-wavelength), and S- (short-wavelength) cones
This is the most common mutation in the rhodopsin gene, causing autosomal dominant retinitis pigmentosa; it is responsible for 10% of RP in the US
P23H
This disease is caused by a dominant G38D mutation (rod transducin), leading to the oldest known form of autosomal dominant stationary nyctalopia (constitutively active rods that do not degenerate)
Nougaret Disease
This disease is a form of stationary nyctalopia that is caused by a homozygous defect in codon 309 of the gene for the protein arrestin; it produces as frameshift mutation with truncation of the protein. This disease is also caused by null mutations of rhodopsin kinase.
Oguchi Disease
This disease is caused by null mutations of the guanylate cyclase gene, causing a childhood autosomal recessive form of RP that shows genetic heterogeneity
Leber Congenital Amaurosis (LCA)
This disease is caused by recessive defects of the ABC transporter proteins; mild defects cause macular degeneration, intermediate ones cause cone-rod dystrophy, and severe ones cause RP (heterozygous defects are found in 4% of cases of AMD)
Stargardt Disease
This disease is caused by defects of the L-type calcium channel gene, a protein that seems to determine transmitter release from the rod synaptic terminal that may also affect cones
X-linked Stationary Nyctalopia
Mutations in this gene can lead to several disorders, including ADRP, macular degeneration, pattern macular dystrophy, vitelliform macular dystrophy, butterfly macular dystrophy, and fundus flavimaculatus
Peripherin/RDS (PRPH2)
This is a protein found in cochlear hair cells and in the cilium of connection rod inner and outer segments; heterozygous mutations cause Usher syndrome type I (deafness + vestibular ataxia at birth with development of autosomal recessive RP)
Myosin VIIA
Heterozygous missense mutation of this gene produces Best disease, a dominantly inherited form of macular degeneration that involves the entire RPE layer but causes damage only in the macula; it codes for a chloride channel found on the basolateral surface of the RPE
Bestrophin
Heterozygous point mutations of this gene produce Sorsby macular dystrophy; its protein inhibits metalloproteinase that regulates the extracellular matrix (antiangiogenesis factor)
TIMP3
Homozygous defects of this gene causes retinitis punctata albescens; the protein facilitates 11-cis-retinal formation and shields the plasma membrane from the potential lytic effects of its aldehyde moiety
CRALBP (cytoplasmic retinal-binding protein)
Homozygous defects in this enzyme cause fundus albipunctus, a form of stationary nyctalopia; the enzyme forms 11-cis-retinal from 11-cis-retinol
11-cis-retinol dehydrogenase
A single heterozygous mutation of this gene causes Malattia Leventinese (Doyne honeycombed retinal dystrophy), a dominant form of macular degeneration
EFEMP1 (EGF-containing fibrillin-like extracellular matrix protein)
This is an X-linked gene that is involved in prenylating Rab proteins, which facilitates their binding to cytoplasmic membranes and promoting vesicle fusion; its X-linked mutation causes choroideremia
REP-1 (Rab escort protein-1)
Homozygous defects in this gene cause gyrate atrophy; the enzyme breaks down ornithine which, in high concentrations, seems toxic to the RPE
Ornithine Aminotransferase (OAT)
Homozygous defects in this gene cause abetalipoproteinemia, or Bassen-Kornzweig syndrome, a condition characterized by autosomal recessive RP and the patient’s inability to absorb fat (treatable with fat-soluble vitamins)
MTP (microscomal triglyceride transfer protein)
Homozygous defects in this gene cause infantile Refsum disease, with RP, cognitive disabilities, and hearing defects; the gene codes for peroxins (needed for peroxisome biogenesis)
PEX1
Homozygous defects in this gene cause Refsum disease (with RP, cerebellar ataxia, and peripheral neuropathy); the enzyme degrades phytanic acid and is located in peroxisomes, and patients with Refsum disease may be treated with a phytanic acid-restricted diet
PAHX
These cells are inhibited by glutamate transmitter released by cones; they are excited (turned on) when light hyperpolarizes the cones and inhibited (turned off) when a shadow depolarizes the cone)
On-bipolar cells
These cells are excited by glutamate transmitter released by cones; they are inhibited (turned off) when light hyperpolarizes the cones and excited (turned on) when a shadow depolarizes the cone)
Off-bipolar cells
These are antagonistic interneurons that inhibit photoreceptors by releasing GABA when depolarized; their dendrites synapse with cones. One class modulates L and M cones, and another class S cones. A thin axon terminal emanates from the cell body and sends dendrites to rods. This provides negative feedback. When light hyperpolarizes cones, it stops its transmitter release, causing these cells to also hyperpolarize (turn off), stopping the release of GABA and depolarizing the cone.
Horizontal cells
These are non-neural retinal cells that play a supportive role to neural tissue, extending from the inner segments of the photoreceptors to the ILM, which is formed by their end-feed. They buffer the ionic concentrations in the extracellular space, seal off the subretinal space by forming the external limiting membrane, and may play a role in vitamin A metabolism of cones.
Müller cells
These cells structurally support the retinal capillary endothelial cells; they play a role in the autoregulation of retinal blood cells. Their loss leads to increased permeability and the development of microaneurysms.
Pericytes
Five crucial functions of the RPE
1) Rhodopsin regeneration (via 11-cis-retinaldehyde)
2) Phagocytosis of shed photoreceptor outer-segment discs
3) Transport of nutrients/ions to photoreceptors and removal of waste products
4) Absorption of scattered and out-of-focus light via pigmentation
5) Adhesion of the retina
This molecule is derived from photosensitive membranes and is responsible for generating the signal detected in fundus autofluorescence imaging.
Lipofuscin
This is the most common electrophysiologic test for evaluating the RPE. It measures the trans-RPE potential.
Electro-oculogram (EOG)
These are molecules or atoms that possess an unpaired electron, making them highly reactive toward other molecular species.
Free radicals
This is a process by which oxygen is activated electronically by light to form singlet oxygen, which in turn reacts at a diffusion-controlled rate with unsaturated fatty acids or other cellular constituents.
Photo-oxidation
This acts as a major scavenger of active oxygen species in the lens. It is first synthesized in the lens epithelium and then migrates to the lens cortex and nucleus. Its levels decline significantly with age.
Glutathione (GSH)
This vitamin scavenges free radicals in the retina. Retinal levels increase until the sixth decade of life and then decrease (which coincides with the age at which the incidence of AMD increases in the population).
Vitamin E
These two carotenoids (xanthophylls) are present in the Henle fiber layer of the macula (the former is dispersed in the retina, whereas the latter is concentrated primarily in the fovea).
Lutein and zeaxanthin
This is the concentration of an active drug at the therapeutic site.
Bioavailability
This is the cycle of a drug through the body, which includes the drug’s absorption, distribution, metabolism, and excretion.
Pharmacokinetics
This refers to the biological activity and clinical effects of a drug.
Pharmacodynamics
This refers to the administration of a drug so as to reach a given clinical endpoint (such as prevention or treatment of disease).
Pharmacotherapeutics
This refers to the adverse effects of either medications or environmental chemicals, including poisoning.
Toxicity
Average volume of a therapeutic eyedrop.
50-μL
The average volume of the tear lake in the blinking eye of an upright patient, before and after instillation of an eyedrop.
7-μL -> 10-μL
Amount of atropine in a 1% solution.
1g/100ml, or 10mg/1ml
Amount of epinephrine in a 1:1000 solution
1g/1000ml, 1mg/1ml, or 0.1%
This is the prodrug of acyclovir
Valacyclovir
This is the prodrug of penciclovir
Famciclovir
This device was designed to deliver pilocarpine at a steady rate of 40μg/hr (equivalent to 2% pilocarpine QID), but with significantly reduced miosis and induced accommodation.
Ocusert delivery system (discontinued after pilocarpine use decreased)
This is the physical process of moving charged molecules by an electrical current. It places a relatively high concentration of a drug locally where it can achieve maximum benefit with little waste or systemic absorption.
Iontophoresis
Three actions of direct-acting muscarinic agonists.
1) Miosis (also shifts forward the lens-iris diaphragm)
2) Accommodation (contraction of circular fibers of ciliary muscle, relaxing zonular tension)
3) Increased aqueous outflow (contraction of longitudinal fibers of ciliary muscle, putting tension on scleral spur and opening trabecular meshwork)
Unwelcome ocular side effects of topical muscarinic therapy.
Miosis, cataractogenesis, induced myopia
Systemic adverse effects of muscarinic agonists.
Salivation, diarrhea, urinary urgency, vomiting, bronchial spasm, bradycardia, diaphoresis
2 classes of cholinesterase inhibitors (including examples of each)
Reversible (physostigmine, neostigmine, edrophonium) and Irreversible (echothiophate/phospholine iodide, diisopropyl phosphorofluoridate, demecarium bromide) Inhibitors
Long-term use of this medication may cause toxic reactions from systemic absorption of local anesthetics containing ester groups (eg, procaine). It may also cause prolonged respiratory paralysis when succinylcholine is administered during anesthesia induction.
Echothiophate (phospholine iodide)
Ocular side effect of phosphorylating cholinesterase inhibitors (eg, echothiophate) in children and adults, respectively.
Iris pigment epithelial cysts (children) and cataract formation (adults)
This medication can be used to prevent iris cyst development in children taking phospholine iodide.
2.5% phenylephrine drops
