prefi CL Flashcards by Norhannafarina Hamdag

TYPES OF CL CL ACCORDING TO MATERIAL (4)

● PMMA
● HEMA
● RGP (CAB) Cellulose acetate butyrate
● SiHy

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Hard CL is similar to ___when it comes to the size

RGP

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Soft CL hugs the cornea and goes beyond the____

HVID/corneal
diameter

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ACCORDING TO WEARING SCHEDULE (5)

● Extended Wear Lens
● Frequent Wear Lens
● Daily Wear Lens
● DISPOSABLE
● Daily Disposable

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ACCORDING TO WATER CONTENT (3)

● LOW 20-40%
● MEDIUM 41-60%
● HIGH >60%

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“best” Cl since it has ____ water content due to its balance. Stable and Durable

MEDIUM 41-60%

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ACC. TO DESIGN (5)

● MONOCURVE
● BICURVE
● TRICURVE
● MULTICURVE
● ASPHERIC

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Has “blends” that smoothens the two curves.
This is the transition between the curves.

TRICURVE

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ACCORDING TO POWER (3)

● Spherical
● Toric
● Multifocal

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Multifocal are dependent to ____ size. For presbyopic patients.

pupil

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multifocal CL: alternating rings of near and distance powers

concentric

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multifocal CL: the near power is at the center and gradually transitions to distance (edges)

aspheric

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multifocal CL: near power is below the distance power, flatter bottom prevents rotation

segmented

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ACCORDING TO PDA CLASSIFICATION (3)

I. LOW WATER(<55%), NON-IONIC
Below 55
II. HIGH WATER(>55%), NON IONIC
Above 55
III. LOW WATER(<55%)IONIC
IV. HIGH WATER(>55%)IONIC

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It repels dirt. Also, it is hard to clean
since it is slimy.

Non-Ionic

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attracts everything. It attracts dirt, protein deposits,
easy to get dirty. but easy to clean.

Ionic

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SOFT LENSES ALTERNATIVE NAMES (6)

● HYDROPHILIC
● HYDROGEL
● GEL
● FLEXIBLE
● LIMBAL & SEMI SCLERAL, LIMBAL & PARALIMBAL
● PLIABLE

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SOFT LENSES SIZE: GENERAL DESCRIPTIONS

● RANGE OF TDs
=13-15MM
● MOST COMMON TDs
=13.5-14.5MM

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When the CL is on the cornea, it touches 3 points. ____

The cornea’s shape is spherical in the center going flat towards the periphery sowhen the CL is placed, there are remaining spaces.

corneal apex
limbus
peri-limbal region

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WHEN TO FIT SPHERICAL SCL? (4)

● LENS OF FIRST CHOICE
Unless the power of the eor of px is above 5.00
so you have to consider other lenses
● EOR’s-Sph & Cyl (<0.75 D cyl)
● Comfort is prime issue
● Low and extreme EOR’s including aphakia

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SCL PERFORMANCE REQUIREMENTS
Soft lenses must: (4)

● PRODUCE GOOD AND STABLE VERSION
● PROVIDE MINIMAL PHYSIOLOGICAL
DISTURBANCE
● BE WEARABLE FOR PRACTICAL PERIODS
● BE COMFORTABLE

SOFT LENSES CENTRATION
There are two ways to measure centration:

● Cartesian System
● Binasal System

Cartesian coordinates is ____.

Mono

Binasal system is Bino. We now take into consideration the nose of the px.

Anything that goes toward the nose is _____ and anything outside/temporal of the nose is negative.

Up is positive and down is negative.

positive

FITTING DESCRIPTION

● GOOD, OPTIMUM, IDEAL ● STEEP, TIGHT, BOUND ● FLAT, LOOSE, MOBILE (moving) ● CENTERED, DECENTRED ● LOW RIDING (loose), HIGH RIDING (steep) ● SUPERIOR, INTERIOR, NASAL, TEMPORAL AND COMBINATIONS OF THE ABOVE

WHAT GOVERNS LENS FIT?

● RELATIONSHIP BETWEEN SAGITTAL HEIGHTS OF LENS AND ANTERIOR EYE(LENS>EYE) ● ANTERIOR EYE TOPOGRAPHY INCLUDING CORNEA ● BLINK-INDUCED PRESSURE ● PHYSICAL PROPERTIES OF THE LENS ● LID CHARACTERISTICS, LID/LENS INTERACTION

PHYSICAL PROPERTIES OF THE LENS (4)

- PHYSICAL PROPERTIES OF MATERIALS - RX - THICKNESSES - LENS DESIGN Thickness and Rx is connected. The thickness depends on the Rx of the px.

HOW IS LENS FIT ALTERED?

Either we manipulate the base curve or manipulate the diameter. We cannot alter the topography of the eye, Rx, Lid characteristic.

BY ALTERING ONE OR MORE FACTORS WHICH GOVERN LENS FIT BUT … THE CONSTANTS ARE: (3)

● ANTERIOR EYE TOPOGRAPHY ● RX ● LID CHARACTERISTICS

SOFT LENS FITTING (Parameter Selection) (14)

● Total diameter ∅T ● BOZR, r0 ● Centre thickness, tc ● Optic Zone Diameter ● Water Content ● Material Selection ● Method of manufacture ● Total diameter ∅T ● BOZR, r0 ● Centre thickness, tc ● Optic Zone Diameter ● Water Content ● Material Selection ● Method of manufacture

For every increase in the total diameter of 0.5mm, you should also increase the base curve by 0.3 mm to maintain the same fitting characteristic.

Rule of Thumb (Soft Lenses)

rule of thumb sample: Example: TD- 14mm BOZR- 8.1mm However in your clinic, the lens that you have is only 14.5mm. So since the TD is increased by 5, you must adjust the base curve so it would be 8.04 mm.

SOFT LENS FITTING (BOZR Selection) Measure Ks (mm) then add either:

* 0.3 - 0.9 mm to flattest K * 1 mm to average of Ks * 4 D flatter than average K Select lens of nearest BOZR from ∅T trial set

WHAT TO ASSESS DURING LENS TRIAL Observe decentration and/or lag:

● Primary gaze (0.2 - 0.75 mm acceptable) ● Upgaze (up to 1.5 mm acceptable) ● Lateral eye movements (up to 1.5 mm acceptable)

The need for Corneal Coverage: Mechanical prevention of (3)

● corneal trauma ● limbal trauma ● conjunctival trauma

The need for Corneal Coverage: Optical (3)

● centration (often decentred up, sometimes up and out) ● shape regularity ● post-lens tear film uniformly

The need for Corneal Coverage: Physiological (3)

● corneal exposure this will cause dryness ● corneal dessication ● tear film disturbance, lens & eye wettability

The need for Corneal Coverage (4)

optical mechanical prevention comfort physiological

About 1 mm symmetrical overlap is ____

ideal

Soft Lens Fitting (Effect of a Blink) (2)

Too steep Flat

- the vision is clear immediately after a blink. - Before and after blinking= clear

Too steep SCL

- Vision is blurred immediately after a blink. - Because it goes out of place

Flat SCL

Why is CL movement required? (3)

● Removes and disperses ocular debris ● Promotes tear exchange (minimal) ● Possibly aids epithelial wetting by mucin spreading and smoothing.

Lens movement of Soft CL depends on (7)

* Lens type * Lens design * Physical properties of lens ● material especially rigidity * Fitting relationship * Lid factors * Anterior eye topography

What is not acceptable? (4)

* Lens edge curling/wrinkling - too loose (slit-lamp or pen torch will disclose) * Conjunctival indentation - too tight * Excessive decentration exposure * Excessive movement producing visual disturbances.

It is useful to remember that ___ dehydration tends to tighten the fit.

on-eye

Excessive Looseness Indications: (4)

* If extreme, lens will not stay in eye * Excessive lens movement * Wrinkling/buckling of lens edge * Vision variable but worse immediately after blink if decentred - if lens centred blink may be little or no difference

Tint Selection

Handling: Enhancing

- full diameter – light tint to avoid halo - iris diameter

handling

- for lighter colored eyes only - usually, tint similar to iris e.g. blue or aqua lens – blue eyes

Enhancing

Back Vertex Power (BVP)

● Spectacle Rx = VD corrected ● Add trial and over Rx BVP’s ● Calculate best sphere

Calculate best sphere

- If low to moderate astigmatism present: 4:1 rule - Reduced VA may be acceptable for “social” wear - If BS fails to provide required VA, consider toric SCL