Optics 500 - Study Guide

Palpebral Fissure

The opening between the upper and lower eyelids when the eye is open.

Layers of the cornea (anterior to posterior)

1. Epithelium

2. Bownman's Layer

3. Stroma

4. Decements Membrane

5. Endothelium

Endothelium

The last layer of the cornea. This layer is mainly responsible for maintaining corneal dehydration by pumping out excess water and controlling the thickness.

Corneal layers that regenerate without scarring

1. Epithelium - heals without leaving a scar

3. Decements Membrane -heals without leaving a scar

Polymegathism

Overlapping of cells in the endothelium due to chronic edema and PMMA contact lenses. Different-sized cells.

Corneal Apex

steepest part of the cornea

Aspheric Cornea

Steeper in the center, and the surface gets progressively flatter at the edge. The overall shape of the cornea.

Cornea

The clear tissue that covers the front of the eye.

Power of the cornea

+43.00 Diopters

Radius of the cornea

7.85 mm

Neovascularization

growth of abnormal new blood vessels in the cornea.

Tear Layers (outside in)

1. lipid layer

2. aqueous layer

3. mucous layer

lipid layer

outer layer of the tear film which slows down evaporation. (oily layer)

Average blink rate

12-18 blinks per minute

Crystalline Lens

it is the second most refractive structure of the eye. This lens is inside the eye, which allows changing focus. It has a total power of +19.00 Diopters

Cataracts

clouding of the lens. When the crystalline lens has lost its transparency.

Aphakia

absence of the crystalline lens, usually after cataract surgery. The patients prescription then changes to a very high plus.

Corneal contact lens diameter range:

between 7mm - 11 mm in diameter

Semi-sclera contact lens diameter:

between 12-15 mm in diameter

Scleral contact lens diameter

up to 25 mm in diameter

IPC

Intermediate Posterior Curve- always flatter than CPC and steeper than PPC.

CPC

Central Posterior Curve, also called the Base Curve. This is the steepest curve.

PPC

Peripheral Posterior Curve- always flatter than the base curve

OZ

Optic zone - the central zone of a rigid contact lens that contains the refractive power (Rx)

Junctional Zone (JZ)

The junction of the two curves on the back surface of the contact lens.

Chord Diameter

The overall diameter of a contact lens from one edge to the other edge.

LT: Larger diameter = tighter fit

Base Curve

also known as the CPC. The steeper the BC, the tighter the CTL

DK

oxygen permeability. Measures the amount of oxygen that moves through the CTL plastic material.

Dk/L

oxygen transmissibility. The ability of oxygen that reaches the cornea. Where L is the center thickness. The higher the DK the thinner the lens the more oxygen reaches the cornea.

EOP

Equivalent oxygen percentage. Measures how much oxygen actually reached the cornea while the contact lens in on the eye. For successful CTL wear, the EOP must be at least 7%

Hypoxia

lack of oxygen. When oxygen supply falls lower than 7%

Lenticular

Used for high plus and high minus CTL. Lenticular zone has no refractive power.

Myoflange

lenses for high plus prescriptions. Example: +10.00 D

Hyperflange

lenses for high minus prescriptions. Example: -12.00D

Diagnostic Lenses

Dx/Trial Lens. The best fitting method to fit contact lenses

LLP

lacrimal lens power

Keratometer

instrument used to measure the curvature of the cornea. Used for fitting contact lenses. Measurement is taken at every doctors visit.

Radiuscope

Measures base curve of a contact lens and detects lens warpage

Topogometer

Attachment to make keratometer more accurate

Pachometer

A medical device used to measure corneal thickness.

Slit-lamp

evaluates contact lens fitting. General inspection of anterior surface of the cornea, evaluates contact lens and cornea relationship and detects abnormal stainings.

With The Rule Astigmatism

WTR - the steepest curve is in the vertical meridian (90-degree axis). For example, K's: 44@180/45@90. There is more power @ 90

Against The Rule Astigmatism

ATR - the steepest curve is in the horizontal (180-degree axis). For example, K's: 45.75@180/44.50@90. There is more power @ 180

Oblique Astigmatism

When meridians contain the greatest difference along the 45 & 135 degree axis. For example, K's: 43.50@45/44.50@135

Irregular Astigmatism

meridians not 90 degrees apart. For example. K's: 45@126/46@85

Central Pooling

The fluorescent pattern of a tight contact lens will show fluorescein accumulating in the center of the lens. (Bubbles in the center)

Central Touch

The fluorescent pattern of a loose contact lens will show little to no fluorescein in the center, and all the fluorescein will accumulate on the outer edge of the lens. (Bubbles on the edge)

Bubbles at the center

fluorescent pattern of a tight contact lens.

Peripheral pooling

fluorescent pattern of a loose contact lens.

Corneal astigmatism

The astigmatism that results

from the surface of the cornea (measured by the

keratometer). This is the difference in horizontal and vertical k-readings.

Spectacle Astigmatism

The amount of astigmatism found in the refractive prescription (cylinder and axis of Rx)

Residual Astigmatism

Astigmatism left uncorrected. (leftover) Solve using SA-CA=RA

Back Toric Contact Lens Design

RGP design ordered if corneal astigmatism (CA) is equal to or more than 3.00 diopters

Front Toric Contact Lens Design

RGP design ordered if residual astigmatism (RA) is more than 1.00 diopters

BiToric Contact Lens Design

RGP design if CA is equal to or more than 3.00 AND RA is more than 1.00 diopters