Unit 1 Flashcards
When the px is behind the phoropter and eye chart is placed at infinity where (feet and meters)
20 feet
6 meters
When using the phoropter to measure at near where do we measure (inches and centimeters)
16 inches
40 cm
what is the goal when correcting refractive errors
To focus the image on the fovea
we use lenses to move the focal point of an image onto the retina
Is retinoscopy objective or subjective?
Objective
Parts of retinoscope?
-Forehead rest
-Peep Hole
-On/Off
-Magnet for fixation targets (dynamic ret)
-Streak window
-Brightness
-Dust-free sealed optics
-Cross linear polarization filter switch
-Sleeve (ALWAYS DOWN)
Why is it important for the sleeve to be down for ret
To produce divergent light rays and a diffuse, unfocused beam of light
This position is termed plano, or plane mirror effect and is required for proper neutralizatino
When the collar is up what does it do?
Emits convergent light rays and a sharper beam
-This position is termed concave mirror effect, and is used for certain advanced techniques
Where is the fixation target during ret?
-20/200 letter / non accommodative target
-Important to give a target so px is not looking at light // if they look at the light the pupil will constrict and accommodation may be triggered which results in a more myopic result
During ret when the reflection is “off axis” what does this inidicate?
Astigmatism
During ret when the light “scissors” what does this indicate?
Kerataconus
During ret we evaluate streak at 90,45,180 and 135 .. what do we evaluate?
-If the streak looks the same in every direction the refractive error is spherical or close to it
-If the beam is not parallel to the streak this means astigmatism
How to change the angle of the streak on ret?
Rotate the collar
how to know if we are working in sphere for ret?
Because cyl is always in negative so we work with the more positive (least negative)
Devices used to quantify tonometry
-Indentation- Indent (depress) using a fixed weight
-Applanation- Flattening a specific area
Tonometry is good to use for pxs with what?
Glaucoma, key in early detection
Successful management of glaucoma
-monitoring IOP at regular intervals
-Observing optic nerve
-Verifying the integrity of the pxs visual field
pathway of how acqeuous humor flows through the eye
Ciliary body
Pupil
Anterior Chamber
Trabecular meshwork
Schelmms canal
Episcleral veins
Systemic bloodstream
purpose of aqueous humor
-provides nutrients to the cornea and lens
-Create an internal pressure necessary to maintain shape of the glope
-If this system falls out of balance then the optic nerve can be damaged which can lead to gluacoma
what happened in 1865
Albertch von graefe was one of the first to propose an instrument to assess pxs pressure
what happened in 1884
cocaine use to anesthtize the eye
early 1900s
Schiotz mechanical tonometer was introduced / became the “gold standard” for measuring IOPS
1950s
goldmann applanation tonometer came into use
-this became the preffered method of testing and has remained for 50+ years
What is tonometer measured in
mmHG (millimeters of mercury)
Average / normal IOP ??
10 to 22 mm Hg
What is ocular hypertension
when IOP exceeds 22 mm Hg but other diagnostic testing is normal
Factors affecting IOP
-ocular structures
–scleral rigifity
– centreal corneal thickness
-Extraocular influences
Scleral rigity
Sclera is abnormally “tough” and resists “give” when an indentation devicfe is applied to the cornea
-Conversely, an abnormally ‘elastic’ sclera gives tooo much causing a false low reading
Centreal corneal thickness
plays an important role in the accuracy of IOP measurements and in the risk of developing glaucoma
Average CCT ?
555um (micrometer)
Thinner cornea ?
<555um
will elicity artifically low IOP due to less resistance by cornea
Thicker cornea?
> 555um
will yield falsely high IOP readings
what are some extraocular influences?
-body position
-diurnal curve
-ocular profusion pressure
what can body position effect IOP
-IOP is lowest in a sitting position
-increase overnight when in a reclining position
Diurnal curve
over a 24 hr period, IOP normally fluctuates 2 to 6 mm Hg
-In glaucoma pxs, can be greate than 10 mm Hg
Ocular profussion pressure
relationship between IOP and systemic blood pressure
-Systemic blood pressure drops, it decreases the OPP
Clinical skills
-Palpation
-Indentation
-Applanation (contact / non contact)
Palpation
-Tacticle or digital palpation
-Eye w. elevated pressure will feel more rigid
Palpation advantages
-no special equipment is needed
-can be performed in any location
-anesthic drops are not required m
-SImple, non threatening means to guage IOP in young children
Palpation technique
Ask the px to close their eyes - not to squeeze them shut
-W/ the index and middle finger, gently press on the central globe through the eyelid
Indentation
-Measure the distortion of the cornea when acted upon by an external force
-Converted to an equivalent IOP
Indentation tool
Schiotz tonometer
-Premier indentation tonometer
Indentation technique
-Instil topical anesthetic
-have px recline
-hold eyelids open and ask px to breath slowly and fixate on the ceiling
-footplate is slowly lowered perpendicularly onto the cornea
-record the measurment and use the chart to convert the reading to mmHg
Applanation
-Measure the force required to flatten a standard area of the cornea
-displaces much less aqueous in comparission to indentation
Tools for applantation
-goldmann applanation tonometry
-perkins
-pneumotonometer
-Icare
-Tono pen
-Dynamic contour tonometry
Goldmann applanation tonometry
-consists of a funnel shaped prism with a flat applanating surface
-tip creates two semicircular mires when applied to the corneal surface
Technique of Goldmann applanation tono
-instill combined anesthetic drop w. fluroscien dye into the eye
-seat px comfortably at the slit lamp. Examine the corneal surface to make certain its healthy
-Swing tonometer into position. Prism should be rotated to the 180 degree position (unless there is 3D or more of cyl)
-Set mag to lowest power, switch cobalt blue, open the light to the biggest section and position light at an angle between 45 and 60
-move the prism forward until it makes contact w the central cornea
-turn the force adjustment knob until the inner edges of the mires are just toughing eachother
How to record pressure from goldmann applanation
read the number on the force adjustment knob. Multiply the reading by 10 to convert it to IOP in mm Hg
how to disinfect goldmann tip
-soak in hydrogen peroxide 0.3 or household bleach for 10 mins. Rinse with saline and pat dry
Perkins
-Hand-held battery-operated, portable applanation tonometer
-principles are essentially the same as goldmann
If a px had a high IOP and we were doing palpation how would it feel?
It would feel hard / firm
Pneumotonometer
-Regulated flow of air runs from an internal pump through a tube to a probe-The probe detects the force of air flowing through it and the force of resistance as it slightly indents the cornea
-The balance of these two forces represents the IOP
Technique of pneumotonometer
-Turn on device
-Ensure good air flow (no kinks in the hose)
-Administer anesthetic and have px focus straight ahead
-Gently place the tonometer tip against the pxs central cornea
-A “beep” (change in tone) will signal when a measurement has been obtained
Icare
-Utilizes the principle of “rebound technology”
-Magnetized coils propel a tiny, disposable probe onto the cornea
-bounces back once it makes contact
-the firmer the eye (higher the IOP), the faster the probe rebounds
-Useful as a screening tool for uncooperative pxs or children
-Home-monitoring device where the px is trained to use themselves
ICare technique
-No calibration or anesthetic needed
-Insert a fresh probe into the base
-Hit the measurment button once (00 will appear)
-Adjust forehead support so the device is aligned properly
-Ask the px to look straight ahead. Press the measrument botton
-Six measurments are made consecutively.
-Once all 6 are obtained, the IOP reading will be displayed following a “P”
Tono-Pen
-Translate mechanical deformation of the cornea into an electrical signal
-Some devices require daily calibration prior to use
-Portable and easy to use in any position
-Not very accurate when testing in the very high or very low ranges
Tono-Pen techniques
-Administer anesthetic drops
-Instruct the px to focus on a distant object
-Ensure a fresh tip cover is in place (confirm px does not have latex allergy)
-Direct the tip perpendicularly to within 1/2inch of the center of the pxs cornea.
-Press the operators button once (8888) will appear on display “====” should appear followed by a beep / begin measuring
-Briefly touch then remove the tonometer tip from the corneal surface
-A chirp will sound when a valid IOP is obtained
-After a given number of valid measruments are acquired a final been will sound
Dynamic contour tonometry (DCT)
-Eliminates errors inherent in measuring IOP caused by corneal rigidity or thickness
-A microscope analyzes the force measurements and the ocular pulse amplitudes
-Takes 100 readings per second
-Measures pulsatile IOP directly and continuously (dynamically)
-Attaches to the slit lamp
Cons with Dynamic contour tonometry
Takes longer than GAT
Increased contact time with cornea
Price
Non contact applanation tonometry
-Air puff tonometer
-Diation
-Ocular response analyzer 8 (ORA)
Air Puff Tonometer
-Uses infared and photoelectric sensors to calculate the time it takes for a standardized pulse of air to flatten the cornea
-Great screen device
-Tend to read IOP 2.7 to 3 mmHg higher compared to GAT / confirm suspicious measurments with GAT
Air puff tonometer - does a soft eye take longer or shorter
Takes a shorter amount of time in comparison to a firmer one
Diaton
-Hand-held, pen like device that takes IOP transpalpebrally (through the eyelid) px is looking up
-Essentially we are measuring the scleral not the cornea
-Does not directly touch the cornea
-Works on “ballistic principle”, which is similar to indentation
-Discrepancy between the diaton and GAT
-Accurate readings require precise placement of the tip of the correct eyelid location
Ocular Response Analyzer 8 (ORA)
-Emits a noncontct pulse of air, which pushes the cornea in until it becomes slightly concanve (past the usual depth achieved by applanation)
-The cornea rebounds to its original convex shape
-The system captures both readings
-The difference between these readings is the corneal hysteresis (CH)
-Numbers are averaged and converted to IOP
what does CH stand for and mean?
Corneal hysteresis
-CH is the ability of the cornea to absorb and dissipate energy
Potential risks of tonometry ?
-Any method of tono should be avoided in all cases of corneal ulcer or orbital trauma
-Caution when taking IOP on an infected eye (may spread infection to the opposite eye or other pxs)
-Corneal abrasion / scratch
-Rubbing the eye while anesthetized
what is Vasovagal Reaction and what can happen to px
-Result of a stimulation in one branch of vasovagal nerve which can cause you to faint
-Px may become very quiet and suddenly feel unwell
-Nauseous or warm
-Pale, sweaty, or clammy
What to do when Vasovagal reaction happens to a px
-Stop procedure
-Have px lower their head or recline chair backward to bring hear at/or below level of the heart
-Tell px to take slow, cleasning breaths
-Call for help, DO NOT leave px unattended
-Reaction usually last for less than a min with a full recovery
-Be cautions of a second reaction when the px stands up
-Check blood pressure and pulse before allowing px to leave
-Document reaction in the chart for future refrence
