PBL REPORTSPECIAL SENSE SYSTEMMODULE 1: DECREASE IN VISUAL ACUITY

GROUP MEMBERIIN BANISWIRAC 111 08 193ELDIE RAHIM PRADANAC 111 08 217NEERMALADEVI PARAMASIVAMC 111 08 755THIAGARAJAN KANDAPANC 111 08 763MOHD. ALIFF HALIMIEC 111 08 770NUR ADILAH BT SHAHARUDDINC 111 08 779ZALIKHA BT MOHD NASIRC 111 08 787NAZIRUL MUNIR BIN ABU HASSANC 111 08 795NURAYSHA NURULLAHC 111 08 803MUHAMMAD HAFIY BIN MOHD RUSLIC 111 08 808SUDARMANC 111 07 022RADINAL IRWINSYAHC 111 07 043MUHAMMAD ZULFADLY NURALIMC 111 O7 077RICHA GUNAWAN TANRAC111 07 094THIBAN SHAARMA A/L JAIEPALANC 111 07 333

TUTOR: DR. dr. Habibah S.M., Sp.MCASES SCENARIO: DECREASE IN VISUAL ACUITY A 56 year old man came to the Ophthalmology outpatients clinic with main complaint of decrease in visual acuity. No history of spectacles usage, red eye and eye trauma previously.

Clarification: Visual acuity Red eye

Keywords: 56 years old man Chief complaint: decrease in visual acuity No history of spectacles usage, red eye and eye trauma

Questions:1) What is the anatomy of the eye?2) What is the histology of the eye?3) What is the physiology of the eye?4) What is the relationship between age and decrease in visual acuity?5) What is the possible location of the lesion?6) What is the mechanism of red eye?7) What is the examination to diagnose visual acuity test?8) What are the main criteria in usage of spectacle?9) What is the epidemiology in visual acuity?10) What is the possible differential diagnosis?

Answers:1) What is the anatomy of the eye?

The three tunics of the eyeball are as follows: The outer fibrous layer (tunica fibrosa), consists of two regions: the sclera and cornea. The sclera (white of the eye) covers most of the eye surface and consists of dense collagenous connective tissue perforated by blood vessels and nerves. The cornea is the transparent region of modified sclera that admits light into the eye. The middle vascular layer (tunica vasculosa), also called the uvea; consists of three regions: the choroid, ciliary body, and iris. The choroid is a highly vascular, deeply pigmented layer of tissue behind the retina. The ciliary body, a thickened extension of the choroid, forms a muscular ring around the lens. It supports the iris and lens and secretes a fluid called the aqueous humor. The iris is an adjustable diaphragm that controls the diameter of the pupil, its central opening. The iris has two pigmented layers; one is a posterior pigment epithelium that blocks stray light from reaching the retina and the other is the anterior border layer, which contains pigmented cells called chromatophores. High concentrations of melanin in the chromatophores give the iris a black, brown, or hazel color. The inner layer (tunica interna), which consist of the retina.The optical components of the eye are transparent elements that admit light rays, bend (refract) them, and focus images on the retina. They include the cornea, aqueous humor, lens, and vitreous body. The cornea has been described already. The aqueous humor is a serous fluid secreted by the ciliary body into the posterior chamber, a space between the iris and lens. It flows through the pupil into the anterior chamber between the cornea and iris. From here, it is reabsorbed by a ringlike blood vessel called the scleral venous sinus (canal of Schlemm). Normally the rate of reabsorption balances the rate of secretion. The lens is suspended behind the pupil by a ring of fibers called the suspensory ligament), which attaches it to the ciliary body. Tension on the ligament somewhat flattens the lens so it is about 9.0 mm in diameter and 3.6 mm thick at the middle. When the lens is removed from the eye and not under tension, it relaxes into a more spheroid shape and resembles a plastic bead. The vitreous body (vitreous humor) is a transparent jelly that fills the large space behind the lens. An oblique channel through this body, called the hyaloids canal, is the remnant of a hyaloid artery present in the embryo.

The neural components are the retina and optic nerve. The retina forms from a cup-shaped outgrowth of the diencephalon; it is actually a part of the brainthe only part that can be viewed without dissection. It is a thin transparent membrane attached at only two pointsthe optic disc, where the optic nerve leaves the rear (fundus) of the eye, and its scalloped anterior margin, the ora serrata. Directly posterior to the center of the lens, on the visual axis of the eye, is a patch of cells called the macula lutea50 about 3mm in diameter. In the center of the macula is a tiny pit, the fovea centralis, which produces the most finely detailed images for reasons that will be apparent later. About 3 mm medial to the macula lutea is the optic disc. Nerve fibers from all regions of the retina converge on this point and exit the eye to form the optic nerve. Blood vessels enter and leave the eye by way of the optic disc.

The accessory structures of the eye include the eyebrows, eyelids, conjunctiva, lacrimal apparatus, and extrinsic eye muscles. The eyebrows probably serve mainly to enhance facial expressions and nonverbal communication, but they may also protect the eyes from glare and help to keep perspiration from running into the eye. The eyelids, or palpebrae, block foreign objects from the eye, prevent visual stimuli from disturbing our sleep, and blink periodically to moisten the eye with tears and sweep debris from the surface. The eyelids are separated from each other by the palpebral fissure and meet each other at the corners called the medial and lateral commissures (canthi). The eyelid consists largely of the orbicularis oculi muscle covered with skin. It also contains a supportive fibrous tarsal plate, which is thickened along the margin of the eyelid. Within the plate are 20 to 25 tarsal glands that open along the margin. They secrete an oil that coats the eye and reduces tear evaporation. The eyelashes are guard hairs that help to keep debris from the eye. Touching the eyelashes stimulates hair receptors and triggers the blink reflex. The conjunctiva is a transparent mucous membrane that covers the inner surface of the eyelid and anterior surface of the eyeball, except for the cornea. Its primary purpose is to secrete a thin mucous film that prevents the eyeball from drying. It is richly innervated and highly sensitive to pain. It is also very vascular, which is especially evident when the vessels are dilated and the eyes are bloodshot. Because it is vascular and the cornea is not, the conjunctiva heals more readily than the cornea when injured. The lacrimal apparatus consists of the lacrimal (tear) gland and a series of ducts that drain the tears into the nasal cavity. The lacrimal gland, about the size and shape of an almond, is nestled in a shallow fossa of the frontal bone in the superolateral corner of the orbit. About 12 short ducts lead from the lacrimal gland to the surface of the conjunctiva. Tears function to cleanse and lubricate the eye surface, deliver oxygen and nutrients to the conjunctiva, and prevent infection by means of a bactericidal enzyme, lysozyme. Periodic blinking spreads the tears across the eye surface. On the margin of each eyelid near the medial commissure is a tiny pore, the lacrimal punctum. This is the opening to a short lacrimal canal, which leads to the lacrimal sac in the medial wall of the orbit. From this sac, a nasolacrimal duct carries the tears to the inferior meatus of the nasal cavitythus an abundance of tears from crying or watery eyes can result in a runny nose. Once the tears enter the nasal cavity, they normally flow back to the throat and we swallow them. When we have a cold, the nasolacrimal ducts become swollen and obstructed, the tears cannot drain, and they may overflow from the brim of the eye. The extrinsic eye muscles are the six muscles attached to the walls of the orbit and to the external surface of the eyeball. The extrinsic muscles move the eye. They include four rectus (straight) muscles and two oblique muscles. The superior, inferior, medial, and lateral rectus originate on the posterior wall of the orbit and insert on the anterior region of the eyeball, just beyond the visible white of the eye. They move the eye up, down, medially, and laterally. The superior oblique travels along the medial wall of the orbit. Its tendon passes through a fibrocartilage ring, the trochlea, and inserts on the superolateral aspec of the eyeball. The inferior oblique extends from the medial wall of the orbit to the inferolateral aspect of the eye. Most of the extrinsic muscles are supplied by the oculomotor nerve (cranial nerve III), but the superior oblique is innervated by the trochlear nerve (IV) and the lateral rectus by the abducens (VI).

2) What is the histology of the eye?The eyeball has three layers. The innermost layer is the retina. The middle layer is the uvea. The outer layer is the sclera and cornea.There are ten layers to the retina. The retina contains receptor cells, neurons, pigmented epithelium and supporting cells. The retina consists of the rods, cones, bipolar cells, ganglion cells, horizontal cells, and amacrine cells. The receptors for vision are the rods and cones. The rods are located on the periphery, and are not color sensitive. The cones are the receptors for color. Muller's cells are part of the retina. The anterior pigmented portion of the retina is called the ora serrata. The nervous element in the retina consists of bipolar cells and ganglion cells. The neurons in the retina are bipolar. A bipolar neuron has two process that branch from it: an axon and a dendrite. Bipolar neurons are not very common and are found in some of the organs for special senses. Bipolar neurons are found in the retina, inner ear, and the region of the nose involved with smell. The fovea centralis is part of the retina. There are only cone cells in the fovea centralis. It is the site for maximal visual acuity.The uvea is the middle layer of the eyeball. It consists of the iris, choroid and ciliary body. The most anterior portion of the uvea is the iris. The iris is the colored part of the eyes. The vascular pigmented structure of the uvea is the choroid. The inner layer of the choroid is the lamina vitrea. The lamina vitrea is also referred to as Bruch's membrane. The ciliary body is a thickening in the uvea. It contains the ciliary muscle. The ciliary muscle is within the ciliary body. The ciliary muscle adjusts the shape of the lens.The sclera is composed primarily of collagen fibers. The cornea is transparent and avascular. The cornea is composed primarily of collagen fibers. There are five layers to the cornea: epithelium, Bowman's membrane, substantia propria, Descemet's membrane, and endothelium. Bowman's membrane and Descemet's membrane are acellular. The majority of the cornea is from the substantia propria. The endothelium is a simple epithelium. The surface of the cornea is covered by a non keratinized stratified squamous epithelium. The lamina cribrosa are small openings within the sclera where the fibers forming the optic nerve travel through.

3) What is the physiology of the eye?Eyes consists of several structure generally if we looking from outside which are Iris, Palpebra, Conjunctiva, Sclera, and Pupils.Visual Pathway had been helped by mechanism of refraction.

Refraction is the change in direction of a wave due to a change in its speed. This is most commonly observed when a wave passes from one medium to another at an angle other than 90.Inside the eyes, several structure plays role as refractive medial in visual pathway which is1. Cornea2. Aqueous Humor3. Lens4. Vitreous BodyThe refractive media function to refract the light that passed through the eyes and focus them into the retina (fovea).Fovea contain high visual acuity compared others part of the retina. Light that passing through the eyes first will penetrate into cornea, aqueous humor, lens and vitreous body before it reach fovea. Each refractive medium give different refractive index.Refractive Index:1. Air 1.002. Cornea1.383. Aqueous Humor1.334. Lens1.405. Vitreous Body1.34

Eyes have special ability in focusing image at fovea. It can control the shape of the lens to make it short and fat for near object and long and thin for distant object. This mechanism is facilitating by help from ciliary muscle and suspensory ligament.

When the light penetrates into the retina, several chemical reactions will occurs. This mechanism called phototransduction.Phototransduction is the complex process whereby the energy of a photon is used to change the inherent membrane potential of the photoreceptor. This change thereby signals to the nervous system that light are in the visual field.Activation of a photoreceptor cell is actually a hyperpolarization; when they are not being stimulated, rods and cones depolarize and release glutamate continuously. In the dark, cells have a relatively high concentration of cyclic guanosine 3'-5' monophosphate (cGMP), which opens ion channels (largely sodium channels, though calcium can enter through these channels as well). The positive charges of the ions that enter the cell down its electrochemical gradient change the cell's membrane potential, cause depolarization, and lead to the release of the neurotransmitter glutamate. Glutamate can depolarize some neurons and hyperpolarize others.When light hits a photoreceptive pigment within the photoreceptor cell, the pigment changes shape. The pigment, called iodopsin or rhodopsin, consists of large proteins called opsin (situated in the plasma membrane), attached to a covalently-bound prosthetic group: an organic molecule called retinal (a derivative of vitamin A). The retinal exists in the 11-cis-retinal form when in the dark, and stimulation by light causes its structure to change to all-trans-retinal. This structural change causes it to activate a regulatory protein called transducin, which leads to the activation of cGMP phosphodiesterase, which breaks cGMP down into 5'-GMP. Reduction in cGMP allows the ion channels to close, preventing the influx of positive ions, hyperpolarizing the cell, and stopping the release of neurotransmitters. The entire process by which light initiates a sensory response is called visual phototransduction.

4) What is the relationship between age and decrease in visual acuity?

Uncorrected visual acuity may begin to decrease in a normal healthy person around age 50. Optically, the eye becomes more hyperopic (farsighted; the point of focus falls behind the retina because the cornea is too flatly curved or the axial length is too short) and astigmatic (nonspherical curvature of the cornea or lens causes light rays to focus at different points) with aging. Subtle neurologic changes in brain functioning can cause visual acuity involving fast-moving objects to decline, resulting in the perception of decreased visual acuity. "Normal 20/20 vision" may not be obtainable in the very old.

5) What is the possible location of the lesion?

Location Examples of disease

Cornea Glaucoma

Aqueous HumorGlaucoma

LensCataract

Vitreous HumorPosterior Vitreous Detachment

RetinaDiabetic Retinopathy

Optic NerveOptic Neuritis

Optic ChiasmPituitary Tumor

Lateral Geniculate NucleusInjury

Visual CortexStroke/ Aneurysm

6) What is the mechanism of red eye?

Generally, red eye is a symptom that inflicted by many diseases. Red eye is defined as the abnormalities that change the eye colour to red, including the bulbar and the skin surrounding the eye such as palpebra. The examples of red eye seen involve localized dense haemorrhage in subconjunctival haemorrhage, the red, dry or flaky periocular skin in contact dermatitis, generalized conjunctival redness, or tarsal conjunctival redness in viral conjunctivitis. The mechanism of red eye differs on each disease. It may involve overgrowth of cornea by thickened or degenerative conjunctiva such as in pterygium, post operation infection, obstruction of gland opening at the edge of eyelid such as in chalazion, trauma, or even a forceful cough which make a direct blow that burst the blood vessels of the eye. Commonly, it involves the dilation of blood vessels in conjunctiva or episclera, which happened due to the increase blood flow to this area.Below are some of the causes and the examples of diseases that accompanied by red eye:

7) What is the examination to diagnose visual acuity test?

Vision TestsVision tests check many different functions of the eye. The tests measure your ability to see details at near and far distances, check for gaps or defects in your field of vision, and evaluate your ability to see different colors. Visual acuity tests are the most common tests used to evaluate eyesight. They measure the eye's ability to see details at near and far distances. The tests usually involve reading letters or looking at symbols of different sizes on an eye chart. Usually, each eye is tested by itself. And then both eyes may be tested together, with and without corrective lenses (if you wear them). Several types of visual acuity tests may be used. Refraction is a test that measures the eyes' need for corrective lenses (refractive error). It is usually done after a visual acuity test. Refractive errors, such as nearsightedness or farsightedness, occur when light rays entering the eye can't focus exactly on the nerve layer (retina) at the back of the eye. This causes blurred vision. Refraction is done as a routine part of an eye examination for people who already wear glasses or contact lenses, but it will also be done if the results of the other visual acuity tests show that your eyesight is below normal and can be corrected by glasses. Visual field tests are used to check for gaps in your side (peripheral) vision. Your complete visual field is the entire area seen when your gaze is fixed in one direction. The complete visual field is seen by both eyes at the same time, and it includes the central visual field-which detects the highest degree of detail-and the peripheral visual fields. Color vision tests check your ability to distinguish colors. It is used to screen for color blindness in people with suspected retinal or optic nerve disease or who have a family history of color blindness. The color vision test is also used to screen applicants for jobs in fields where color perception is essential, such as law enforcement, the military, or electronics. Color vision tests only detect a problem-further testing is needed to identify what is causing the problem.

Visual acuity testVisual acuity is a measure of the spatial resolution of the visual processing system and is usually tested in a manner to optimize and standardize the conditions. To this end black symbols on a white background are used (for maximum contrast) and a sufficient distance allowed to approximate infinity in the way the lens attempts to focus. Twenty feet is essentially infinity from an optical perspective (the difference in optical power required to focus at 20 feet versus infinity is only 0.164 diopters). Whilst in an eye exam lenses of varying powers are used to precisely correct for refractive errors, using a pinhole will largely correct for refractive errors and allow VA to be tested in other circumstances. Letters are normally used (as in the classic Snellen chart) as most people will recognize them but other can be used instead.In the term "20/20 vision" the numerator refers to the distance in feet between the subject and the chart. The denominator is the distance at which the lines that make up those letters would be separated by a visual angle of 1 arc minute, which for the lowest line that is read by an eye with no refractive error (or the errors corrected) is usually 20 feet. The metric equivalent is 6/6 vision where the distance is 6 meters. This means that at 20 feet or 6 meters, a typical human eye, able to separate 1 arc minute, can resolve lines with a spacing of about 1.75mm. 20/20 vision can be considered nominal performance for human distance vision; 20/40 vision can be considered half that acuity for distance vision and 20/10 vision would be twice normal acuity. The 20/x number does not directly relate to the eyeglass prescription required to correct vision, because it does not specify the nature of the problem with the lens, only the resulting performance. Instead an eye exam seeks to find the prescription that will provide at least 20/20 vision.A visual acuity of 20/20 is frequently described as meaning that a person can see detail from 20 feet away the same as a person with normal eyesight would see from 20 feet. If a person has a visual acuity of 20/40, he is said to see detail from 20 feet away the same as a person with normal eyesight would see it from 40 feet away. It is possible to have vision superior to 20/20: the maximum acuity of the human eye without visual aids (such as binoculars) is generally thought to be around 20/10 (6/3) however, recent test subjects have exceeded 20/8 vision. Some birds, such as hawks, are believed to have acuity of around 20/2; in this respect, their vision is much better than human eyesight.When visual acuity is below the largest optotype on the chart, the reading distance is reduced until the patient can read it. Once the patient is able to read the chart, the letter size and test distance are noted. If the patient is unable to read the chart at any distance, he or she is tested as follows:

Tools using for visual acuity test Snellen chart Sloan letters Landolt C E Chart Golovin-Sivtsev Table

Classifying low visionAnyone with reduced vision not corrected by spectacles or contact lenses can be considered to be visually impaired. The World Health Organization uses the following classifications of visual impairment. When the vision in the better eye with best possible glasses correction is: 20/30 to 20/60: is considered mild vision loss, or near-normal vision 20/70 to 20/160: is considered moderate visual impairment, or moderate low visionLegal blindness 20/200 to 20/400: is considered severe visual impairment, or severe low vision 20/500 to 20/1,000: is considered profound visual impairment, or profound low vision More Than 20/1,000: is considered near-total visual impairment, or near total blindness No Light Perception: is considered total visual impairment, or total blindnessThere are also levels of visual impairment based on visual field loss (loss of peripheral vision).

8) What are the main criteria in usage of spectacle?

An eyeglass prescription is an order written by an eyewear prescriber, such as an optometrist or ophthalmologist, that specifies the value of all parameters the prescriber has deemed necessary to construct and/or dispense corrective lenses appropriate for a patient.If an examination indicates that corrective lenses are appropriate, the prescriber generally provides the patient with an eyewear prescription at the conclusion of the exam. In fact, in the United States, the FTC (Federal Trade Commission) requires eyewear prescribers to give each patient a copy of their prescription, immediately following the concluding exam, even if the patient doesn't ask for a copy. The parameters specified on spectacle prescriptions vary, but typically include the power to which each lens should be made in order to correct blurred vision due to refractive errors, including myopia, hyperopia, astigmatism, and presbyopia. It is typically determined using a phoropter asking the patient which lens is best, computer automated refractor, and through the technique of retinoscopy. Opticians are not eye doctors and, therefore, are not licensed to write an eyeglass prescription. A dispensing optician will take a prescription written by an optometrist or ophthalmologist and order and/or assemble the frames and lenses to then be dispensed and sold to the patient.The most important characteristic of a lens is its principal focal length, or its inverse which is called the lens strength or lens "power". The principal focal length of a lens is determined by the index of refraction of the glass, the radii of curvature of the surfaces, and the medium in which the lens resides. For a thin double convex lens, all parallel rays will be focused to a point referred to as the principal focal point. The distance from the lens to that point is the principal focal length of the lens. For a double concave lens where the rays are diverged, the principal focal length is the distance at which the back-projected rays would come together and it is given a negative sign. For a thick lens made from spherical surfaces, the focal distance will differ for different rays, and this change is called spherical aberration. The focal length for different wavelengths will also differ slightly, and this is called chromatic aberration.The lens power and the type of lens are very important in correcting one's vision problems and the only way to establish the right power and type of lens a person needs is by visiting an eye doctor. Although some people buy their eyeglasses on the shelf, individuals who need their vision corrected are recommended to use prescription glasses according to their needs because otherwise their problems will worsen in time.Prescriptions for eyeglasses are measured in diopters. The measurement starts at zero ("plano"), with four quarters to a diopter: 0.25 (a quarter diopter), 0.50 (one half a diopter), 0.75 (3/4 of a diopter), and 1.00 (one diopter). The higher the numbers, the higher (stronger) the prescription.Here are estimates for the approximate correction needed for each line seen on the Snellen chart:Snellen 20/1020/1520/2020/3020/4020/5020/10020/200Estimated prescription Plano (zero)PlanoPlano to -0.25-0.50-0.75-1.00 to -1.25-1.75 to -2.00-2.00 to -2.50

Degree of Farsighted VisionJust like myopia, the degree of hyperopia is measured in diopters, which are units of measurement that describe lens strength. Myopic prescriptions have negative numbers and measurements of hyperopia are made with positive numbers. A person with a prescription of +2.0 diopters or less has mild hyperopia. A degree of hyperopia of between +2.0 and +4.0 diopters considered moderate. Someone who is severely farsighted will need a prescription of +4.0 diopters or higher.

9) What is the epidemiology in visual acuity?The study population was composed of 9980 persons, ages 20 to 84, from the general population of Copenhagen, Denmark.Results:The age-standardized prevalence rates of visual impairment and blindness were 0.66% and 0.20%, respectively, and rose significantly with age (P