Intro to CL Flashcards
First real contact lens
made by adolf fick -> scleral contct lens of blown glass
Hard CL
made of PMMA or polymethylmethacrylate
resistent but no oxygen allowed
used 1950-1980
Modern GP lenses (gas permeable)
1st gen GP: polycon, CAB
dia b/n 8.5-9.5 mm
-low oxygen transmitters
2nd gen GPs (Boston, Fluoroperm, etc)
- addition of siloxane to allow more oxygen
3rd gen GPs (Menicon-Z, Contex Paragon CRT)
- daily wear 30 continuous
- used for high cl rx errors
- more oxygen permeable than soft cl
- orthokeratology
Soft lenses (hydrogels)
Soft lenses has HEMA:
-oxygen and water attached to methacrylate
-soft and flexible -> improvement of comfort
-silicone hydrogels for extended wear
(B&L soflens, Vistakon)
silicone hydrogels (SiHy) for extended wear
Who developed HEMA
Dr. Otto Wichterle and Professor Drahoslav Lim
from a children’s toy
CL indications
Optical correction: myopia, hyperopia, astigmatism, aphakia, presbyopia, irregular astig
therapeutic: bandage lens for corneal disease, drug delivery to cornea and ant. seg
amblyopia: fogging or occluder lens
corneal reshaping: reduction of RE, myopia control
prosthetic: cosmetic enhancement
Keratoconus and irregular corneas (enabling these patients to see)
Caution with contact lenses
Pinguecula and pterygia
dexterity problems
hygiene considerations
environment concerns
severe allergies
dermatological problems: acne rosacea, stpah lid disease, psoriasis, eczema
allergies and respiratory disorders: Rhinitis, sinusitis, hay fever, and asthma tend to produce conj. injection and increased ocular sensitivity w/ cl
pts with sac (seasonal allergic conj.)
allergy symptoms: itching, tearing, photophobia, burning, mucus, increased tear debris
dry eyes, glaucoma, DM, thyroid dysfxn, herpetic disease, immunocompromise (HIV)
ocular side effects of systemic medication
oral antihistamines and decongestants: reduction in tear flow and increased dryness
acutane (acne medication): reduces meibomian secretion and increases dry eye symptoms; corneal infiltrates
diuretics (for edema and hypertension) can cause lid and conj. allergic rxn
valium: mydriasis, photosensitivity
dry eye: antihistamines, decongestants, oral contraceptives, antihypertensives, anticholinergics, muscle relaxants
refractive changes: topomax, oral contraceptives, acetazolamide
mydriasis: anti-cholinergics, anti-psychotics, antihistamines
miosis: codeine
ocular irritation: gold salts, salicylates
altered behavior: disulfuram (antabuse)
CL wear in the US
40.9 million americans 18 and older wore CL in 2014 => 17% of US adult population
10% GP, 20% soft, 2% hybrid, 67% silicone hydrogel
Soft contact lenses
hydrophilic
hydrogels (35-75% water)
- soft,pliable
- comfortable
oxygen transmission
- ^H2O => ^ O2
- dec. thickness => ^ O2
soft lenses - semi scleral
CL care and maintenance
huge industry
cleaning/rinsing/storing/disinfecting
purpose: limit deposit build up, kill harmful micro-organisms
toxic preservatives
compliance problems
Daily wear cl
worn during waking hours; removed before sleep; must be cleaned and disinfected before re-use unless daily disposable; replaced daily, 2 weeks, or monthly
extended wear cl
all day wear, including sleep;
typically worn 1-2 weeks without removal; if removed, must clean and disinfect if lenses are to be re-worn (max. 1 month)
greater risk of complications with extended wears usage
continuous cl
extended wear with no lens removal until such time that lens is to be replaced (typically monthly); no reuse; includes bandage contact lens wear
- can wear 1-2 weeks without removal
disposable frequent replacement cl
daily disposable cl
- eliminates care regimen
- lower complications of DW
- safest, most convenient way to wear CLs
varieties of DCL/FR CLs
- correct myopia, hyperopia, astigmatism and presbyopia
- tints for handling and for enhancing or changing color
- uv blocking
silicone hydrogels revolutionized the industry
silicone hydrogel gives highest oxygen content
Types of rigid cl
PMMA lenses
Gas permeable lenses
hybrid contact lenses
PMMA lenses
made of transparent rigid plastic material called polymethylmethacrylate (PMMA)
excellent optics, no transmit oxygen
replaced by gp lenses
Gas permeable lenses (GP or RGP lenses)
Rigid cl that look and feel like PMMA but allow oxygen to pass through them
advantage over soft/silicon hydrogel lenses is sharper optics due to rigid nature of lens material
hybrid contact lenses
comfort of soft/silicone hydrogel and clear optics of rigid gas permeable
rigid gas permeable central zone surrounded by skirt of hydrogel or silicone hydrogel material
Rigid lens design advantages
superior vision
durability
ease of care
added eye health safety characteristics
ability to correct irregular astigmatism
myopia control for young patients
disadvantage of rigid lenses
initial discomfort (try to keep using positive terms)
allow dirt and dust under lens
unstable for sports or activities
requires more chair time and skill to fit
-teach upper lid touches lens
Patient control on RGP
educate on benefit of RGP
be positive and watch your terminology
avoid: hurt, discomfort, irritation, blurry, hard
substitute: initial awareness, lid sensation, tickling, itchy, water, firm
Anesthetic use
Concerns: staining, effect of eye rubbing, potentially misleads patient
benefits: sensitive patient become less apprehensive, accelerates time for diagnostic lens evaluation
Contact lens for special needs
keratoconus and irregular corneas
bandage lenses for disease
red-green color deficiency and achromatopsia (restores color vision to distinguish colors)
prosthetic lenses (for albinism, aniridia, coloboma)
contact lens fitting
evaluation of trial cl to determine rx
primary fitting criteria: good vision, good comfort, satisfactory physiological response
important role of centration and movement
goal: determine back surface design that is neither too steep nor too flat
prefitting data for GP lenses
pupil size (and location)
palpebral fissure size
eyelid position
HVID (horizontal visible iris diameter): limbus to limbus horizontal
eyelid tension
blink (rate, frequency, fullness)
iris color
keratometry (mire quality)
lid positions
if lid margin is at limbus = 0
if lid margin covers limbus = +
if lid margin is away from limbus (sclera showing = -
blink types
partial
complete
twitch (rgps only)
forced
cl workup includes
keratometry and/or corneal topography
updated manifest refraction and acuities
- always adjusted for vertex distance to corneal plane when over +/- 4.00 D
- prysbyopia/add determination
slit-lamp biomicroscopy
lid eversion
vital dyes: sodium fluorescein, rose bengal, lissamine green
remember: decrease vertex to cornea = less minus or more plus RX for glasses to CL
sodium fluorescein
use in sterile strip form
used to prescreen corneal epithelium for healthy cl wear (no uptake) and to rule out dry eyes
used to evaluate GP patterns on eyes
used for post-cl wear health evaluation
vital dyes
rose bengal is chemically related to sodium fluorescein; may sting on insertion; technically somewhat toxic to epithelium
lissamine green in non-toxic and does not sting
both rose and lissamine green are intracellular dyes:
- stain devalized, desiccated cells (dry eye)
- they both stain walls of dendrites in HSV keratitits where active virus resides
vital dyes stain intracellular: will be devitalized and stain walls of dendrites => active cells
sodium fluorescein stains inter-cellularly
grading of stain
temporal 1/3
central 1/3
nasal 1/3
on scale of 0 - 3
keratometry
measures corneal curvature
only central area
used to fit types of CLs
baseline for early disease detection
corneal topography
keratometry measure only 4 pts (2 in each of two principle meridians)
corneal topography: typically measures 15,000 to 20,000 points all over cornea
preliminary examination of ant. segment
eyelids
conj.
tears
cornea
anterior chamber
iris and lens
biomicroscopy
used to examine front structures of eyes + surroundings
non-invasive viewing
high mag.
high illumination
inspection of both front and back cell layers of cornea
performed: before cl fitting or cl wear, to establish a ‘baseline’
list for successful contact lens fitting
wearing time
comfort
vision
physiological response
appearance
