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Optical

Accommodation: The act of focusing. It involves the radially shaped muscles, also known as the Ciliary Body, and the Crystalline Lens. As the Ciliary muscles are flexed, the Crystalline Lens is bent. The shape change of the Lens causes the focal point of the light to be moved relative to the Retina.

Astigmatism: Ophthalmic astigmatism occurs when there is an oval shape to the cornea and/or crystalline lens, thereby resulting in different prescriptions in separate meridians. Astigmatism causes difficulties in seeing fine detail. Astigmatism can be often corrected by glasses, contact lenses, or refractive surgery. Astigmatism is quite common, affecting one in three individuals. The prevalence of astigmatism increases with age. Although a person may not notice mild astigmatism, higher amounts of astigmatism may cause blurry vision, squinting, eyestrain, fatigue, or headaches.

Hyperopia: Commonly known as being farsighted, i.e.. it is easier to see things farther away than to focus on near objects, although far objects may also be blurry (just less so). The causes of hyperopia are typically genetic and involve an eye that is too short or a cornea that is too flat, so that images focus at a point behind the retina.

Myopic: Commonly known as being nearsighted, i.e.. it is easier to see close objects than far ones. The causes are often genetic and involve an eye that is too large or a corneal curvature that is too steep, so that images focus at a point in front of the retina.

Presbyopia: Represents the loss of focusing ability due to age. Specifically, the Crystalline Lens grows minimally throughout life but reaches a critical density near age 40. The ever increasing loss of flexibility due to its growth in size and density result in the diminishing focusing ability. The ability to focus on near objects declines throughout life, from about 20 diopters in a child and leveling off at 0.5 to 1 diopter by age 60-65.

Scratch Resistant Coating (SR): A hardened coating placed on spectacle lenses to increase its resistant to abrasions.This coating is not scratch-proof (none are) but it is a lot tougher than the surface it covers.

Anti-reflective Coating (AR): A coating that reduces reflections off of the spectacle lens surface and aids in night driving vision by increasing the light transmittance through the reduction of reflections.

CR-39: The standard plastic resin that spectacle lenses are made of.

Polycarbonate: Thinner and lighter than CR-39, this material is the lens of choice for sports enthusiasts due to its impact resistance for eye protection and safety, and for high prescriptions due to being 20-25% thinner and lighter than a comparable CR-39 lens.

High Index: A denser lens than polycarbonate, albeit slightly thicker and heavier, but nonetheless preferred in higher prescriptions due to better optics and less chromatic aberration.

Chromatic Aberration: The separation of light into its individual wavelengths, also known as a “rainbow” effect, that occurs as light passes through a dense medium.

Anatomical

Conjunctiva: The clear membrane that lines the inner eyelid (Palpebral Conjunctiva), and continues on to cover the sclera (Bulbar Conjunctiva). The Bulbar Conjunctiva is not the white part of the eye, it is merely the clear membrane that covers it.

Cornea: The clear dome that protrudes from the eye. The cornea is very unique, it is the most sensitive part of the body, it is the only clear skin in the body, and it gets the majority of its oxygen supply from the environment rather than a dedicated blood supply. It is the first and the most powerful of 2 lenses that light must pass through as it gets focused to the Retina.

Iris: The colored muscle that constricts or dilates to regulate the light supply into the eye.

Pupil: The opening in the iris that expands or constricts depending on the action of the iris muscles. It is the opening that light passes through on its way to the Retina.

Crystalline Lens: The second and most flexible lens that light passes through. The Crystalline lens is bent by the surrounding Cilliary Muscle to enable focusing. Further growth of the Lens throughout life contributes to Presbyopia and eventually a clouding called Cataracts.

Aqueous Humor: The watery liquid that fills the ocular space between the Cornea and the Crystalline Lens. This fluid is involved in many of the Glaucomas.

Vitreous Humor: The thick gel that fills the space from behind the Crystalline lens to the Retina. This fluid is involved in the formation of Floaters and in Vitreous Detachments.

Retina + Photoreceptors (Rods and Cones): The Retina is made up of millions of Photoreceptors which capture light (the Photoreceptor Head), transform it into a chemical signal (the Photoreceptor Body), and send the chemical message (the Photoreceptor Axon) to the brain’s Visual Center in the Occipetal Lobe. The Rods are most sensitive for motion, peripheral vision, and vision in the dark, and the Cones contribute to color perception and central vision acuity.

Optic Nerve: a misnomer, the “nerve” is actually comprised of millions of nerve fibers which emanate as the axons of each individual Photoreceptor. All of the axons are directed in one direction, the focal point of which then becomes the Optic Nerve as an aggregate of the millions of nerve fibrils which comprise it. There is a natural tunnel in the nerve which blood vessels enter and exit the eye from, this tunnel is referred as the “cup” space and its contours are damaged with Glaucoma.

Pathology

Red Eye/Conjunctivitis/Pink Eye: The small blood vessels sandwiched between the Sclera and the Bulbar Conjunctiva dilate during irritation or infection, giving it a “red” or “pink” look, often times associated with a teary or colored discharge. Contributing factors are allergies, contact lenses, mechanical irritation, and bacterial or viral infection, therefore a visit to an Ophthalmic Physician (Optometrist or Ophthalmologist) is warranted to determine and treat the cause.

Ocular Allergy: Histamine is generally released by sensitized Mast Cells which patrol the ocular surface. The histamine release causes the blood vessels dilation (redness), influx of fluid (congestion), and the itch. Additionally, the histamine serves as a chemical attractant to other immune cell types which further contribute to congestion and scratchiness. Fortunately there are effective allergy eyedrops to greatly reduce the allergy cascade and allow for ocular comfort with or without contact lenses.

Retina Detachment (RD): Nobody wants this, the Retina can separate from the eye and vision can be irreversibly lost if the detachment is not attended to in time. Symptoms typically include the sudden onset of flashes and/or multiple floaters, distorted and or blurry vision that does not improve with corrective lenses, and/or an obstruction to the vision similar to a curtain or flag forming in the vision. The visual symptoms often times progress rapidly over the course of 1-3 days so waiting until Friday 5pm is the worst thing to do since the surgeons and the surgical teams are usually not available on the weekends. It is important to note that only the central 30 degrees of the Retina is observable without dilating the pupils. A routine Dilated Fundus Exam utilizing dilating eyedrops can often identify suspicious retinal defects and prophylactic retinal reinforcement utilizing a laser can avoid serious future consequences. Those at risk for a Retina Detachment are those with high eyewear prescriptions, history of previous ocular injury, and those with active symptoms like flashes of light and numerous or sudden onset of numerous floaters.

Vitreous Detachment (PVD): The Vitreous ages with time and this proteinaceous dense material can separate from the fluid it was mixed with. The protein condensation results in a shrinking effect on the vitreous fluid as a whole. The outer membrane of the vitreous, named the Vitreous Base, pulls off of the Retina and most of the time this separation occurs cleanly although one might experience some brief and mild flashes of light over the course of a few days to a few months, and the vision may permanently become slightly murky due to condensation of the media. However, sometimes the Vitreous Base has abnormally strong attachments to the Retina and the pulling on the Retina during the vitreous separation process can create a Retina tear and an ensuing Retina Detachment. It is important to do a Dilated Fundus Exam utilizing dilating eyedrops to differentiate between a PVD and an RD, it is not uncommon to repeat the dilation a few months later or multiple times if the symptoms persist or become more severe.

Floaters: These are the dark, shadowy objects we see floating in our vision as we look at well lit areas or bright backgrounds. We actually see the shadows of floating condensed protein in the vitreous that can take on the form of a spot, a line, or a complex webbed figure. Floaters are typically normal and fairly common due to the syneresis, or aging, of the fluid in the eye causing the separation of the protein from the vitreous complex. However, a floater can also be due to a “plug” coming off of the retina, termed an “Operculum”, when adhesions from the vitreous form on the Retina and pull on it until it separates. Typically flashing of lights are observed, but not always, so suspicious floaters or sudden onset floaters should be evaluated with a Dilated Fundus Exam.

Cataract: Any opacification of the Crystalline Lens, no matter what the size or density, is technically called a cataract. As the opacity becomes more dense, the vision, contrast and color perception will diminish. The biggest contributing factor to cataracts is age – the Crystalline Lens grows everyday of your life, and as it gets denser and denser, it also gets cloudier and cloudier. Eventually the cloudiness becomes too much to properly see and Cataract Surgery is recommended for safe driving and general mobility. Other contributing factors which can accelerate the age of onset or the progression of cataracts is : UV exposure, Diabetes, radiation, inflammation, trauma, and corticosteroid medications, to name a few.

Macular Degeneration: There are two types of Age-Related Macular Degeneration – Dry and Wet. They are both characterized by the collection of cholesterol-like waste deposits which demonstrate stress to the Retinal Pigmented Epithelium(RPE) – the RPE supports and nourishes the overlying photoreceptors – which can lead to degeneration of the RPE and even influx of fluid into the macula (Wet AMD). When the macular photoreceptors are damaged, central vision is reduced but peripheral vision remains. Contributing factors to AMD is age (50+), smoking, and genetics. Treatment involves daily supplementation of anti-oxidants coupled with Lutein and Zeaxanthin, and intra-ocular injections to cause regression of newly formed leaky blood vessels in Wet AMD.

Glaucoma: Intraocular Pressure (IOP) is created by the dynamics of the production and the drainage of the Aqueous Humour – the fluid within the space of the Cornea and Crystalline Lens. Glaucoma refers to a group of entities which affect the health of the Optic Nerve by way of elevated Intraocular Pressure – ie., Open Angle Glaucoma (OAG) and Closed Angle Glaucoma (CAG) – or if IOP is normal, by way of reduction in blood circulation to the Optic Nerve, ie., Low Tension Glaucoma. To make it even more confusing, a person may have a normal IOP but still be at risk for glaucoma if the Optic Nerve Fibers are (genetically?) too fragile for the eye’s IOP. The progression of Glaucoma is often very slow over decades of life, characterized by thinning of the retina, “notching” of the Optic Nerve, “cupping” (enlargement and deepening) of the tunnel space within the Optic Nerve, and eventual peripheral vision loss. Total blindness occurs if left untreated. Although there is no cure for Glaucoma, control is achieved by eyedrops to lower IOP, and in resistant cases surgery can lower IOP by creating new canals to enhance outflow. Screening for and monitoring of Glaucoma involves taking frequent IOP measurements, peripheral vision testing using a Visual Field Perimeter, imaging the structural components of the Optic Nerve and thickness of the surrounding Retina using a scanner such as the GDX or OCT, and photodocumentation with a Retina Camera.

Pinguecula and Pterygium: Ultra-Violet light can cause damage to the ocular surface, namely the clear membrane (overlying the white of the eye, the Sclera) called the Bulbar Conjunctiva. Since the eye does not contain melanin (it does not tan) it is not protected like the skin on our body so it gets sunburned more easily and more frequently. Eventually the Bulbar Conjunctiva becomes keratinized, a process by which the collagen becomes “leathered” – thickened, elevated, and discolored. Often the area becomes a dry spot since the tears drain from the elevated surface and it becomes exposed. With dryness comes redness, stinging and eventually inflammation. Further UV exposure and/ or chronic dryness may lead to the bulky skin extending onto the Cornea, now called a Pterygium. The more the Pterygium extends towards the corneal apex the more dryness, redness, inflammation and discomfort is experienced. Pingueculae and Pterygiae are treated by using sunglasses and eye drops such as artificial tear lubricants and or steroids. Pterygiae are removed surgically when tear supplementation or steroids cannot sufficiently manage the dry eye or inflammation, and/or when the vision becomes distorted by the growth of the tissue on the cornea.