Eye Flashcards
The painful structures of eye are……, while painless structures are …….
Cornea, iris, ciliary body
Lens, vitreuous body, choroid, retina
Ant 1/6 of eye is protected by….., post 5/6 of eye is protected by…..
Eyelid
Bony orbit
Center and effert of corneal reflex
Midbrain (suprior colluiculus)
Efferent, facial nerve of both sides
Compare Menace & Dazzle reflex
M, blinking after moving object very close to the eye
D, shining bright ligh t in the eye
Explain types of tear secretion
Basal secretion
Reflex secretion due to corneal/conjunctival irritation afferent is by ophthalmic n and efferent is by parasympathetic (facialn.)
Psychic tears: inc tear secretion by emotion: produced by activation of arasymp supply
Lipid layer of tears is secreted by ……, water layer by……. Which contains……proteins. Mucos layer is secreted by…….
Meibomian glands
Lacrimal glands, lactoferrin/IgA
Gobet cells of conjunctiva
Function of mucous in tear film
Make the corneal and conjuctival surface hydrophilic so tears can spread homogenously over surface
Enumerate functions of tear film
Optimizing corneal optic properties, cleansing, healing effects (supply WBCs), nutritive, protective, lubricant
Mention causes of dry eye
Dec tear secretion, vitamin A deficiency, impaired lid function (exposure keratitis)
Write formula for refractive index
RI= Velocity of light rays in air/velocity of light rays in medium
…..has highest refractive index in eye, while……. causes most refraction of light
Lens
Cornea
Mention factors controlling degree of refraction of light
- Refractive index of medium
- Angle of incidence on interface
- Degree of curvature
Define focal length
The distance between center of lens & focal point
Write formula for lens power
Lens power=1/focal length in meter OR 1/object distance+1/image distance
The central point of the eye as a whole lies……
17 mm in front pf the retina
The total refractive power of the human eye is…..
50-60 dipoters
GR: Most refractive power comes from cornea not the lens
Because the greatest difference in refractive index is at the air-cornea interface, so most refraction occurs there while lens is surrounded by aqueous & vitreous humors which have nearly equal refractive index
Describe image orientation of the retina
Retina, images are inverted but they are processed upright by the visual cortex, if retinal images are turned right side up by means of special lenses, the object viewed would look upside down.
Enumerate functions of the cornea
- Transparent structure allows light entry to eye
2, most powerful refractive medium of the eye - Regular curvature important in formation of sharp retinal images
- Has protective function
Describe nutritional supply of the cornea
Diffusion from aqueous humor, limbal capillaries, tear film (85% of O2 needs is taken from tear film)
Mention causes of corneal transparency
Non-keratinized, avascular, substantia propria fibers are regularly arranged, nerves are unmyelinated, tear film keeps cornea moist and prevents dryness, relative corneal dehydration.
Enumerate causes of corneal dehydration
Both epithelim & endothelium act as barriers to prevent excess flow of water to stroma
1. Surface epithelium is connected by tight junctions and has Na/K pumps forming hypo-osmotic stroma & hyperosmotic aqueous humor
2. Endothelial cells have Na-K pump, carbonic anhydrase and Na-H exchanger that maintain low Na conc and consequently water in substantia propria
Enumerate causes of corneal opacity
- Corneal injury that reaches Bowman’s capsule
- Vitamin A def results in xerophthalmia and corneal keratinization
- Corneal vascularization
Functions of the choroid
The choroid’s pigment absorb extra light. That is not absorbed by photoreceptors to prevent blurring of vision
Choroidal bv provide rerina with O2 and nutrients
Secretory part of ciliary body is……while contractile part is…..
Ciliary process
Ciliary muscle
Describe active secretion mechanism of aqueous humor
Major contributor to aqueous formation (80-90%), carried out by non-pigmented epithelial cells as they contain Na-K pumps which actively pumps Na while Cl and water follow passively. Also contains carbonic anhydrase which helps secretion of HCO3 to intercellular spaces .
Describe circulation & drainage of aqueous humor
Episcleral outflow (90%] it passes through trabecular meshwork to canal of Schlemm to the episcleral veins.
Uveo-scleral outflow (10%): passes through ciliary body to be absorbed by bc, scoeral wall to the periocular orbital tissues .
Mention functions of aqueous humor
Maintain IOP, supplies nutrition and drains waste of avascular structures, one of the refractive media of the eye
IOP is….measured by…..
12-20 mmHg
Tonometer
Enumerate functions of IOP
Maintain spheroid shape of eye, exert two forces on normal focusing mechanism, pressure flattening force on lens surface and stretching force on the lens. Maintain lens during rest.
Compare oper & closed angle glaucoma
O, is caused by damage, sclerosis or obstruction of trabecular meshwork which impairs drainage while the irido-corneal angle is opened.
C, closure of irido-corneal angle by root of iris
Mention results of glaucoma
- Failure of accomodation
- Compression of optic n at optic disc leading to optic atrophy, concentric visual field narrowing and finally blindness
- Headache
The power of the lens at rest is…..while at full accomodation is……, that of cornea is…
20 diopters
34 diopters
40 diopters
Enumerate lens functions
It is an important refractive medium (1/3 of eye power)
It has an important role for near vision (accomodation reflex)
The anterior surface of lens compared to pasterior has…….
Higher refractive index with less curvature
What are causes of lens transparency?
It is a avascualr, lacks nerves, fibers are arranegd in regular manner with little extracellular space, high conc of glutathione which keep protein reduced, protein oxidation leads to aggregation and loss of transparency, it contains Na/K ATPase pumps in lens epithelium that extrude Na & Ca and prevent lens swelling & opacification.
Enumerate causes of cataract
Congenital
Old age, due to accumulation of low molecular weight polypeptides in the lens
Exposure to UV or X-rays
1ry to diseases as DM aschigh glucose level activates polyol pathway and leads to sorbitol accumulation. Sorbitol has high osmotic power.
Describe aim & mechanism of bilateral convergence of both eye
This allows the 2 images of the near object to fall on the fovea centralis of both retinas to fall on 2 corresponding points in both eyes and prevent diplopia.
M, contraction of 2 medial recti muscles
Describe the aim of bilateral miosis
Prevents light falling on peripheral parts of the lens so light falls on center of lens. This prevents spherical & chromatic aberration.
Define:
1. Spherical aberration
2. Chromatic aberration
- It is the formation of blurred image due to inability of lens to collect all the light rays into a single focal point. The refractive index of the peripheral parts is different from the central parts resulting ij different refraction and different foci.
- The peripheral parts of lens act as a prism which analyses white light inti spectral components
Describe aim & mechanism of bilateral accomodation
A, increase the power of the lens to collect divergent light rays so the image of object is shifted to the retina.
M, Ciliary muscle contracts, ciliary body is pulled forward and inward, distance netween edges of ciliary body dec, lens ligament relaxes, lens springs into more convex shape, anterior curvature esp inc.
Mention the center and efferent of accomodation refkex
C, superior colliculus in midbrain sends signals to Edinger Westphal n
E, CN III:
1. Parasympathetic fibers from EWN relay in ciliary ganglion for constrictir pupillae & ciliary muscle
2. Somatic fibers from area 19 to area 8 stimulate somatic part of CN III fir MR
In Purkinje-Sasor images, the small upright image is from……, the large upright image is from……, the small inverted image is from…..
What happens when subject looks at nearer object & what can you deduce?
Cornea (convex mirror)
Anterior surface of the lens (convex mirror)
Posterior surface of the lens (Concave mirror)
The middle image of ant lens dec in size the others remian constant
Accomodation changes curvature of anterior lens
Define:
1. Accomodation amplitude
2. Accomodation range
- It is thexdifference between refractive power of the eye when accomodation is relxed and its power when accomodation is maximum
- It is the distance between the far point of distinct vision (fully relaxed accomodation).and near point of distinct vision
Define:
1. Punctum proximum
2. Punctum remotum
- It is the nearest point to the eye at which an object can be seen clearly with accomodation
- It is the farthest point from the eye at which the onject can be seen clearly when accomodation is fully relaxed
Define:
1. Myopia
2. Hypermetropia
- Refractive condition the eye in which parallel rays come to a point of focus in front of the retina while accomodation is at rest, close objects are seen clearly but distant ones are blurred.
- Parallel ray cone to a point of focus behind the retina while accomodation is fully relaxed. Distant objects seen perfectly but not close objects
Describe long-term effects of hypermetropia
Headache & fatigue due to continuous contraction of MR, may also lead to medial squint in children.
Compare myopia & hypermetropia with respect: far point, near point, range of accomodation, ciliary muscle
Myopia: limited, nearer than normal, decreased, poorly developed
Hypermetropia: normal (with accomodation), farther than normal, decreased, well-developed
(IN ORDER OF THE QUESTION)
Compare myopia & hypermetropia with respect:causes & correction
Myopia: long eyeball (each 1mm leads to -3D) OR inc refractive power of lens due to ciliary muscle spasm, lens dislocation, or inc corneal curvature (keratoconus), corrected by concave spherical lens.
Hypermetropia: short eyeball (each 1mm leads to +3D) OR refractive power of lens dec due to abnormal flat lens or paralysis of ciliary muscle or dec corneal curvature (cornea plans), corrected by convex spherical lens.
What happens in presbypoia?
-Gradual loss of accomodation with aging
- The near point recedes away from the eye
-Far point does not change
-Accomodation power & range decrease
Causes of prebyopia & correct.
- Loss of lens elasticity
- Loss of elasticity of choroid
- Liquefaction of vitreous causing loss of lens support
Coorected by convex lens for near vision only
Describe general feature of astigmatism
Refractive condition of the eye in which parallel rays come into different foci resulting blurred image, the refractive power of the eye is not the same in different meridians. Curvature of lens/cornea is not equal or uniform.
Enumerate types of regular astigmatism +definition + correction
Simple: one meridian is emmetropic the other is ametropic.
Cylindrical lens its axis is placed at right angles to diseased meridian
Compound: both meridians are ametropic with different degrees of error.
Sphero-cylindrical lens correction
Mixed: one meridian is myopic the other is hypermetropic, corrected as previous.
Define irregular astigmatism & its correction
All meridians are irregular with keratoconus & corneal scar
Corrected by hard contact lenses to replace the irregular surface of anterior cornea by regular surface of contact lens OR keratoplasty
With respect to cylindrical lens, meridian of axis power is…..while that of perpendicular meridian is……
Zero
Maximal power
Spherical lens focuses light into……, while cylindrical lens focuses light into……
Point
Line
What are effects of albinism on eye?
Pupils appear reddish bec of absence of pigment and blood vessels of choroid can be seen, they also complain of weak vision as a result of reflection of light in all directions.
Enumerate functions of iris
- It regulates the amount of light that enters the eye by controlling pupil size.
- It prevents light passage through peripheral parts of lens
- It protects the retina by dec UV rays
- Increases the depth of focus which is the distance in front and behind the focal point over which the image may be focused without reduction in the sharpness of image.
- Iris mediates pupillary write reflex which is important in diagnosis of many nervous lesion and diseases
Mention center and efferent of pupillary light reflex
C, pretectal nucleus (midbrain)
E, from Edinger Wesphal nucleus of both sides to parasympathetic fibers then ciliary ganglion the postganglionic parasymp fibers to constrictor pupillae
Light reflex on the same side is called…..while on opposite side…..
Direct
Consensual (indirect)
Mention the importance of pupillary reflex
- Help localize the site of lesion in visual pathway: lesion before relaying in pretectal nucleus (loss of light reflex) and vice versa
- Differentiate between stages of anesthesia
- Fixed dilated unreactive pupil helps in diagnosis of death
- Protective reflex
Mention pathological causes of miosis and mydriasis
Miosis, Horner’s syndrome, potine hemorrhage
Mydriasis, occulomotor nerve lesion
Mention effects of each of the following:
1. Amaurotic pupil
2. Argyll Robertson pupil
- Loss of direct light reflex, consensual light reflex intact
- Loss of light reflex with intact accomodation reflex
Function of PE layer
- Black pigment absorbs light no absorbed by photoreceptors preventing its refkection causing diffuse lighting of retina & blurring of vision.
- It stores large wuantities of vit A
- Phagocytose old photopigment discs of photoreceptors
Function of external limiting membrane
Maintains structural stability of retinal cells
Function of horizontal cells
Lateral inhibition for:
1. Determination of visual contrast: when a cone pathway is excited, horizontal cells suppresses activity in surrounding pathways of weakly stimulated or unstimulated cones, sharpens bounds.
2. Determination of colors, there is reciprocal excitation-inhibition nechanism mediated by lateral inhibition vua horizntal & bipolar cells helps in producing color conrast & helps color differentiation.
Classify bipolar cells with explanation
Depolarizing, hyperpolarizing
One of the bipolar cells recieves direct excitation from the rods & cones (via glutamate NT) whereas the other recieves its signal indirectly through a horizontal cell which releases GABA
Function of bipolar cells
Provide additional mechanism for lateral inhibition which is important for separating contrast borders in visual images
Function of amacrine cells
Interneurons of many types help analyze visual signals before they leave retina as:
Some responds to onset of visual signal others respond to offeset in both cases signal dies out rapidly
Some respond to a spot moving across the retina in specific direction, they are said to be directionally sensitive.
Functions of Müller’s cell
It provides mechanical support to retinal cells its ends form outer & inner limiting membranes
It contributes to the metabolism of retina e.g. uptake of NT, removal of debris, storage of glycogen.
Compare parvocellular and magnocellular cells with respect conduction velocity and function
M cells, high conduction velocity concerned with detection of movement and change in loght intensity.
P cells, low conduction velocity & concerned with color vision and detection of fine details.
Function of on-center/off surround (or opposite) mechanism
Helps sharpen and improve discrimination. Also, it has a role in perception of colors.
What happens in case of inc IOP?
Lamina cribrosa will protrude outward forming cupping of optic disc and compress the nerve fibers against the edges, leading to optic nerve atrophy and blindness.
Optic disc can be seen by….., in case of inc ICT appears……., while atrophy appear…..
Ophthalmoscope
Swelling of optoc disc and papilledema
White with wide and deep central cup
Compare positions of optic disc and macula lutea
OD, 1.5 mm in diameter and lies 3 mm medial to post pole of eye
ML, 1.5 mm in d and lies 3 mm lateral to the optic disc at center of retina
GR: Macila appears yellow
Presence of xanthopyll pigment which has a protective role, filtering UV wavelengths that could be harmful to photoreceptors
Macular degeneration causes…..vision
Doughnut
Describe blood supply of retina
Outer 5 layers avascular supplied by diffusion from choroid capillaries
Inner 5 layers from central retinal art
GR: Central retinal art causes sudden and complete blindness
It supplies most layers of the retina
It has no anastomosis with choroidal bv
Retina has no lymphatics and no pain nerve supply
Fovea centralis is….in diameter
4 mm
Compare fovea and extra-fovea with respect: ratio of receptors to bipolar and ganglion cells, blood supply, vision
Fovea: 1:1, diffusion from choroid capillaries, photopic or day vision
Extra-fovea: 200:1, choroid and retinal bvs, scotopic or dim vision
Discs are found in…..and are…..in number in each.
Outer segment of rod and cones
1000
Discs in rods contain…..while in cones contain…..
Rhodopsin/scotopsin
Iodopsin/photopsin
Describe shape of cones
In fovea, long anf thin
In periphery, short and thick
Enumerate types of iodopsin
Erythrolabe, chlorolabe, cysnolabe
Comapre connections of rods and cones
Rods, many rods (100-300) converge on one bipolar cell (convergence)
Cones, peripheral cones converge on one bipolar cell.
In fovea, there is one to one connection
Compare functions of rod and cones
Rods: scotopic (night) vision, peripheral vision, less accurate vision, black/gray/white vision
Cones: photopic (day) vision, central vision, more accurate vision, color vision.
Structure and func of opsin
-found in membranes of the discs and is one of the G protein coupled receptors.
-It determines the molecule’s absorption of light to a particular region of the spectrum
During dark, Na channel proteins of rods and cones remain opened by….., thus membrane potential is…., which is considered…..
cGMP
-40 mV
Depolarized
Describe photochemical changes in photopigment
At light exposure, Rhodopsin decomposes. The only effect of light is the conversion of 11-cis retinal (curved) to all-trans retinal (straight) , this alters configuration of opsin and bleaching occurs. Metarhodopsin-II is formed which activates the associated G prptein called transducin (initiaor orlf electrical events)
Describe electrical events that take place in rods
Transducin activates cGMP phosphodiesterase that causes reduction in cGMP conc leading to closing cGMP-gated Na-channels thus Na inflex is reduced and membrane is hyperpolarized (-70 to -80 mV) which decreases glutamate release amd results in action potential in optic nerve.
Describe the return to resting state of rods and cones
This is done by rhodopsin kinase enzyme which inactivates activated rhodopsin (metarhodopsin II), which reverses the cascade by inactivation of phosphodiesterase,inc conc of cGMP, inc influx of Na, return of membrane potential to resting state.
Name the enzyme which directly reforms 11-cis retinal
Retinal isomerase
Only…..have all-or-none AP in eye
Ganglion cells
Describe intensity discrimination of the eye
The photoreceptor potential is proportional to the logarithm of light intesity.
Receptor potential is faster in…..
Cones
Compare cone and rod adaptation
Cone, the early portion of the curve (5-10 mim) is caused by adaptation of the cones because all chemical events of vision including adaptation occur in cones 4 times faster than the rods.
Rod, the latter portion of the curve (25-40 min) which is slower and greatrr than cones adaptation. The added sensitivity is due to convergence of 100 rods on one ganglion cell in retina these rods summate to increase sensitivity.
Define neural adaptation
When light intensity decreases, the signals transmitted by the bipolar cels, horizontal cells, amacrine cells, gangliom cells are rapidly increased at different stages of transmission in the neural circuit, and vice versa.
Compare neural and chemical adaptation
N, occurs in a fraction of second, fewfold change
C, becomes full after 40 min, many thousandfold change
Purlinje cirve shows that during scotopic vision, maximal retinal sensitivity is…..while in photopic vision……
505 nm (blue-green zone)
550 nm (green-yellow zone)
Define normal visual field
Normal visual field is not circular bec it is limited by anatomical structures
60°upwards, 70°downwards, 60°nasally, 100° temporally
What is the significance of measurement of fueld of vision?
Diagnosing different field defects as:
Generalized field contraction (progressive optic atrophy)
Scotomas: localized areas of blindness
Neurological field defects occur due to lesion in visual pathway
Signals from macular area terminate
…..while those from more peripheral retina terminate……
Lower portion is presented….while upper portion is presented….
Posteriorly (near the occipital pole)
Anteriorly (ant to occipital pole)
Inf, sup
Mention functions of primary visual cortex
- Perception of visual stimuli without understamding their meaning
- Perception of color vision
- Fusion of the 2 images fprmed on both retinas
- Localization of objects in space
Mention functions of 2ry visual areas
- Recognition of the nature of the objects seen and understanding the meaning of various visual sensations
- Localization of object in relation to the observer
- Perception of visual details of colors and their integration with other somatic sensations
- Mediating the accomodation reflex by sending signals to frontal eye field if the details of object are not clear
Define hemianopic pupil and mention an example
Light reflex is obtained only when light falls on one half of the retina (healthy half), while the other half is blind e.g. lesions in optic chiasma or in optic tract
Lesions of optic chiasma
Mention effects of lesion of optic tract lesion
Contralateral homonymous hemianopia
If in ant 2/3: hemianopic pupil, post 1/3: normal reaction
Describe effects of visual cortex
Inf bank of calcarine fissure: contralateral homonymous superior quadrantanopia
Sup bank of calcarine fissure: contralateral homonymous inf quadrantanopia
Both banks of calcarine fissure: contralateral homonymous hemianopia
ALL have macular sparing & normal pupillarycreaction
GR; Lesion of occipital lobe usually have the macula spared
Due to large cortical area of representation, macular representation is separate from that of peripheral fields,
Macular region recieves double blood supply (MCA & PCA)
Capillary heamgiomina may appear within….
6 months of life
Describe etology of retrolental fibroplasia
Developmental disorder occurring in pre-mature or low birth weight infants treated with oxygen. The temporal aspect of retinal periphery is incompletely vascularized, whereas medial aspect is vascularized. Thus the latetal zone is more sensitive to high dose of oxygen therapy and constrict, rendering the tissue distal to this zone ischemic.
Resulting in upregulation of proangiogenic factors such as VEGF, leading retinal angiogenesis. Contraction of the neovasculature may cause retinal detachment.
Mention the most common 1ry ocular malignancy in the white adults in NA ans Europe
Malignant melanomas arisimg from neural crest-derived pigment epithelium of the uvea
Factors of prognosis of melanoma
- Size (lateral extent of the tumor)
- Cell type (tumors containing epithelioid cells have worse prognosis than containing exclusively spindle cells)
- Proliferative index
The most common 1ry ocular tumor in children is….
Describe its familial type
Retinoblastoma
AD trait by RB susceptibility gene located on ch13.
Wavelength of visible light is….
400-700 nm
Define the 3 attributes of color
- Hue: name of color
- Saturation: it is the degree of freedom from dilution with white.
- Brightness: it is the amount of ligh involved.
Define commplementary colours
2 colour when properly mixed give sensation of white
The sensation of any given color is determines by…..
The relative frequency of impulses from each of the cone systems
The primary visual cortex has….layers. …. are. Considered the 1ry areas for color coding
Color blobs
Mode of inheritance of color blindness is…..
Recessive and X-linked
Compare the 3 types of color blindness
Trichromats: have the 3 cone systems but one of them is weak, so individual can recognize deep but not pale color (-anomaly)
Dichromats: have only 2 cone systems which they match their color spectrum with (-anopia)
Monochromats: have only 1 cone system which they match their spectrum with.
Flicker sensation disappears by……….due to…… . The rate at which flicker disappears is called….
Increasing the frequency of visual stimulation
Afterdischarge
Critical fusion frequency
Define corresponding points
Are retinal points at which the image of object must fall to be seen binocularly. They are present at nasal side of one retina and the temporal side of the other retina.
The area of monocular vision is…….
Cresecntric area at the peripheral part of each temopral field
Describe development of binocular vision
- Macular vision starts at 6 weeks
- Binocular fixation starts at 6 months
- Binocular vision development is completed at 6 years
Mention and define grades of binocular vision
Grade I: simultaneous perception it means the brain is able to recieve images from both eyes at the same time
Grade II: the fusion of 2 retinal images to give one mental impression
Grade III: stereoscopic vision (3D)
Enumerate advantages of binocular vision
- It compensates for the weak eye as defect in one eye can be masked by the other
- It is essential for perception of depth
- It gives wider field of view than each eye separately
Define vestibular movements
Are the eye adustments that occur in response to stimuli initiated in semicircular canals, which maintain visual fixation as the head moves.
Define fixation movements and explain its mechanisms
It is movement of the eye to fix on object is visual field to see details of the object, done by 2 neuronal mechanisms:
1. Voluntary fixation: it is voluntary movement of the eye to find the object on which the individual wants to fix vision, done by area 8 (frontal eye field)
2. Involuntary fixation: it is fixes the eyes firmly on the object once it has been found, controlled by area 19 in occipital lobe.
Loss of vision due to neglevt of squinted eye is called……
Ambylopia exanopsia
Describe blood supply & lymph draiange of auricle
BS: posterior auricular & superficial temporal vessels
LD: preauricular, posterior auricular & cervical LNs
The external auditory meatus is…..long
1 inch
The narrowest point of external auditory meatus is……..loacted…..
Isthmus
5mm from tympanic membrane
Blood supply of inner part of EAM
Deep auricular branch of maxillary art
