Glossary

Learning anything, especially medicine, is all about learning a new list of terms and vocubulary.  I am going to try and list them according to disease, but don’t hold me to it!

Parts of the Eye

Tear Film – coats the surface of the cornea.  Everytime we blink, the lids respread our tears to keep the cornea clear.

Cornea – the clear portion in the front of the eye.  The curvature of the cornea accounts for up to 2/3 of the total focusing power of the eye!  The cornea is the clear portion of the eye upon which rests a contact lens.  It is the curvature of the cornea that becomes reshaped when patients undergo laser vision correction.

Anterior Chamber – the fluid filled portion of the eye.  It is the space in front of the iris, but behind the cornea.

Iris - a floppy tissue that gives us the “color” of our eyes, e.g. “blue” or “hazel” eyes actually reflect the color of the iris.  It has a central hole that acts as an aperture, constricting when there is lots of light and dilating in low light.  Neovascularization of the iris (aka rubeosis) can be seen here in diabetic retinopathy and a few other retinal diseases.

Lens – the natural lens sits just behind the iris.  With time, all patients, just like grey hair, will develop cataract – a natural clouding of the eye.  The lens has some focusing power, but not as much as the surface of the cornea.

Vitreous – consists mainly of a “gel” which fills most of the eye.  It is similar to a jelly-fish, in that, it has substance, but is composed mainly of water.  The vitreous has no major role once we are born.  As with the appendix, it is a vestigial tissue, that is, there is no real need for it.  Some would argue it may plug large holes in the eye occurring in trauma.

Retina – the light sensitive tissue the lines the inside of the eye much like wallpaper lines the walls of your room.  Via the optic nerve, it has direct communication with the brain.  The retina must be healthy and attached for us to see well.  If not, regardless of glasses, we may not see.

Optic Nerve – the retina contains millions of thin nerve fibers that coalesce and form the optic nerve.  The optic nerve then exits the eye and connects to portions of the brain…..giving us “vision.”

Choroid – one of the vascular layers of the retina.  It lies underneath the retinal pigment epithelium (RPE) and provides nourishment to the RPE.  Abnormal blood vessels, aka choroidal neovascularization, may originate here and penetrate the other layers of the retina.  This is commonly seen in “wet” macular degeneration.

Retinal Pigment Epithelium – aka RPE.  Lies directly underneath the retina and is in direct contact with the photoreceptors of the retina.  It is principally affected in macular deneration where the RPE cells become sick and may degenerate.  A more uniform loss of the RPE layer is seen in cases of retinitis pigmentosa.

Macular Edema - swelling of the macula.  Commonly seen in diabetic retinopathy.  It may also been seen in cases of wet macular degeneration and other retinal diseases.  It causes blurry vision.

Macular Pucker or Epiretinal Membrane - is a thin “membrane” of protein that covers the macula.  It may cause distortion and/or decreased vision.  It is usually surgically removed if it causes problems.

Sclera – the tough, white wall of the eye.  It is the “white” part of the eye.  It is confluent with the cornea.

Conjunctiva - the thin, vascular, transparent tissue that covers the outside of the eye.  When our eyes get “red,”  the vessels in the conjunctiva get thicker and the eye becomes “redder.”

mTor inhibitor – mTOR (mammalian target of rapamycin) kinase, a key protein in cells that regulates cell proliferation, cell growth and cell survival.  (This is a class of cancer drugs that may have potential application to diabetic retinopathy and wet macular degeneration.  None are presently on the market, but several are in the works.  For example,  Macusight’s Perceiva, a formulation of Sirolimus, an mTor inhibitor.)

VEGF – Vascular Endothelial Growth Factor, a protein that is liberated by the retina and is suspected of causing neovascularization, both in proliferative diabetic retinopathy and “wet” macular degeneration.

VEGF-Trap – an antiangiogenesis treatment under investigation.  This is a protein that mimics the receptor to which VEGF binds.  By binding to the VEGF molecule, VEGF-Trap prevents binding of the VEGF molecule to its receptor.  The VEGF pathway is effectively blocked.  VEGF-Trap is also known as aflibercept.

Lucentis® (ranibizumab) – an anti-VEGF drug.  It is manufactured by Genetech.  It is similar in chemical structure and action to its cousin, Avastin® (bevacizumab).  Ranibizumab is a monoclonal antibody against VEGF-A.  It is FDA approved for treatment of ‘wet” macular degeneration.

Avastin® (bevacizumab) – an anti-VEGF drug.  It, too, is manufactured by Genetech.  It is an antibody directed against VEGF.  It was first developed as an anti-tumor drug and has been used for colon, breast, certain brain, lung and kidney tumors.  It is not FDA approved for use in the eye, but has become standard of care in many areas.

Macugen® (pegaptanib) – an anti-VEGF medication.  It was the first intraocular injection developed for “wet” macular degeneration.  Macugen® is an aptamer directed against vascular endothelial growth factor.

Retinal Detachment – there are really only two types of retinal detachment: rhegmatogenous retinal detachment and traction retinal detachment.

Rhegmatonous Retinal Detachment – a retinal detachment associated with a retinal hole or retinal tear.  The retinal hole or retinal tear allows communication between the retina and the potential space underneath the retina.  This is the most common form of “retinal detachment.”

Traction Retinal Detachment – subtle membranes may develop on the surface of the retina and pull or “tug” on the retina.  This causes a small separation between the top layer of the retina the layers underneath.  There can be subtle loss of vision and/or distortion.

More severe, thicker membranes, can also develop on the surface of the retina and exert significant pulling or “traction” on the retinal surface.  These membranes are more often seen in cases of advanced proliferative diabetic retinopathy.  This is the mechanism by which many patients with diabetes may become blind, from longstanding retinal detachment.  Surgical intervention is usually attempted.

A less common form of traction retinal detachment may also be seen in a disease termed proliferative vitreoretinopathy (PVR).

Lattice Degeneration – a normal peripheral retinal degeneration.  It may be associated with retinal holes and create a retinal detachment.  If caught early, laser photocoagulation may be needed to prevent retinal detachment.

Diagnostics

Slit Lamp Biomicroscopy – the slit lamp is the basic unit to used to examine the eye.  A patient rests his/her chin in the device.  The examiner (doctor) can view the eye using binocular (thereby giving us great depth perception) vision.  A light source, in the shape of a vertical beam, or slit, is of great use in examining the various tissues on the surface of, or deeper into the eye.

Fluorescein Angiography - a diagnostic test using an injectable fluorescent dye.  The dye is usually injected into the arm.  As the dye passes through the retina, abnormalities can be seen in retinal blood flow, neovascularization in “wet” macular degeneration, neovascularization in proliferative diabetic retinopathy, swelling of the retina, etc.

OCT - optical coherence tomography is a relatively new diagnostic device that uses a laser to “scan” the retina.  The retina may be viewed in cross-section or topographically.  Abnormalities in the thickness of the retina may indicate bleeding or fluid accumulation.  It is commonly used to monitor macular edema in diabetic retinopathy and macular degeneration.

Visual Field – a test of the peripheral vision.  The most common tests involve testing the peripheral vision with multiple flashes of light.  The test is non-invasive, does not hurt, but does require the patient to be alert.  Glaucoma is usually monitored by visual field testing.  Certain strokes and tumors may be diagnosed with a visual field.

Color Vision Testing – the macula contains cones, and thus, is the only area of the retina that gives us color vision.  Certain retinal conditions may affect color perception.  Certain glaucomas and diseases of the optic nerves can affect color vision as well.  There are several types of color vision testing.