2 axes of the eye are not 90 degrees apart so they do not create a right angle. This condition cannot be corrected with spectacle lenses and usually requires contact lens fitting and possibly surgery.
The most serious cause of irregular astigmatism is __
keratoconus: caused by a thinning corneal cap where the cornea actually sags or bulges out, causing the irregularity
Binocular vision gives __, which is the ability to see 3D images and use depth perception.
Binocular coordination between the right and left eye is tested with a Titmus kit.
eyes focusing inward to read
For fusion to successfully occur, the images coming from each eye must be within __ % of the size of each other.
If the difference is greater than 5%, the brain will not be able to fuse them together.
Images from the right and left eyes are not the same by more than 5% and the brain cannot achieve fusion
Aniseikonia can be caused by these 2 different conditions:
There is a difference of 2.00 D or more between the OD and the OS prescription. ex. Rx with +5.00 sph OD +1.00 sph OS
when the right and left Rx signs are different, or "against" one another. ex. -1.00 sph OD +1.25 sph OS
Aniseikonia can be corrected with __. If left uncorrected, it can lead to __
- the use of contact lenses or Iseikonia lenses;
- amblyopia (lazy eye)
condition associated with aging in which the eye exhibits a progressively diminished ability to focus on near objects because over time the crystalline lens loses flexibility
This gradual lessening of the power of accommodation due to this crystalline lens losing flexibility becomes noticeable about the age of 40 years
With age and possibly due to exposure to UV rays, the crystalline lens loses transparency becoming opaque
The crystalline lens will be removed surgically and replaced with an intraocular lens (IOL) when the cataract causes the eyes visual acuity to be 20/50 or poorer.
A patient who has an intraocular lens is called a __ patient.
an eye without a crystalline lens, or an eye with a crystalline lens that is unstable
only has one functioning or good eye
Often the Rx will indicate a balance lens for cosmetic reasons for the non-seeing eye. The best balance lens would be the same power as the seeing eye requires.
a term indicating a generalized eye discomfort or eye fatigue of undetermined cause
an absence of all or part of the iris. This condition allows too much light to enter the eye at all times and is usually related to retinal damage as well
can be assisted with an occluding contact lens, or a simple eye occluder if the patient cannot use contact lenses
unequal pupil size - The right and left eye have different sized pupils
can be caused by injury or illness, such as a stroke that has affected only one side of the patient
2 differently colored eyes or irises
Although it does not usually affect the vision of the patient, some are self-conscious and use a tinted contact lens to correct the condition
describes a visually impaired patient whose vision cannot be corrected with spectacles, contact lenses, or a medical treatment or surgery
A patient with a best corrected eye of 20/70 or worse is visually impaired. Visual aids can help this patient to function.
Legally blind is defined as the patient whose correction in the better eye is 20/__ or worse, or __
200; that of a visual field of no more than 20 degrees
A blind patient __. Total blindness means __
- has no ability to see, although light and shadows might be partially perceived at times;
- no light perception (NLP)
acuity (clarity of vision)
electronic testing charts that can be set for different distance simulations and magnification
peripheral vision (field of vision)
The normal patient has a visual field of approx 190 degrees, with the physiological blind spot serving as a reference point to identify which field belongs to which eye. This test can be performed initially with the Amsler grid but more affectively with electronic visual field equipment.
The Ishiharra test and alternate color plates are used to test for color blindness, which can inhibit learning in a child or be challenging to adults in certain occupations.
tests for low vision
Other than acuity, peripheral vision, and color vision, patients are also assessed for glare issues, contrast sensitivity, night vision, depth perception, and regularity of eye movements.
The leading cause of low vision in the world is __. In the US, it is __.
cataract formation; macular degeneration (since cataract surgery is widely available in the US)
Close to follow in the US is diabetic retinopathy, untreated glaucoma, and then complicated or non-treatable cataract.
- also called age related macular degeneration (AMD)
- affects the cones in the macula and can be a wet or dry form of the disease
- marked by a loss of central vision
- Early symptoms are blurred or wavy vision which progresses to central blindess.
- Peripheral vision is often spared.
- Low vision and special aids can help patients.
- caused by a damage to the blood vessels of the light-sensitive tissue at the back of the eye (retina)
- initially may cause no symptoms or mild vision problems
- can eventually cause blindness
- can be caused by an elevated intraocular pressure
- damages the optic nerve and if left untreated, causes blindness
forms of glaucoma: open-angle, closed-angle, congenital
most common form of glaucoma. The aqueous humor does not vacate the eye as quickly as it is produced. can exist without symptoms until vision becomes impaired
can be long term or chronic, or the acute form occurs suddenly. The acute form is caused by the iris angle shutting and causes sudden loss of vision and possibly nausea, vomiting, haloes around lights and pain. Emergency treatment is needed for acute closed-angle glaucoma.
appears soon after a child is born and can manifest as tearing, photophobia and corneal cloudiness. Various surgeries can help.
magnification aid: relative distance
The distance between the patient and the object being viewed is changed.
magnification aid: linear
The object itself is made larger, such as large print books.
magnification aid: angular
can be hand magnifiers all the way to telescopes which make distance objects appear closer and larger
Improving room illumination, providing light sources without glare, control of reflection and increasing the contrast can greatly increase perception by the low vision patient.
used to evaluate distance visual acuity of 20 feet, or optical infinity. format: 20/20, etc
- most common method to check near visual acuity, specifically reading distance
- referred to as the J4 or J2 test
measures intraocular pressure
An IOP higher than average could be a sign of glaucoma or other ocular illnesses.
Non-contact tonometers can use either a puff of air or ultrasound to measure IOP. However, many still use a contact tonometer, such as the Goldman Tonometer, which is usually attached to the slit lamp, or the indentation tonometer.
visual field testing
can reveal the boundary of a patient's peripheral view as well as any irregularities in the peripheral field. This is one of the easiest tests to administer if foveal or macular problems are suspected.
Color perception charts, such as the Ishihara test, are reliable methods of determining any color deficiency. Each plate (with either images or numbers) is specially designed to measure certain colors and specific sensitivity ranges.
The simple grid can help reveal irregularities in a patient's central field of vision. This is often used to diagnose and track macular degeneration.
A patient with 20/20 vision will see all of the lines clear and crisp. A patient with early macular disease might see some of the central lines as warped or wavy. The patient with advanced macular disease will not be able to see lines at all in the center of the grid.
hand held device that allows for the physician to see the internal structures of the eye and retina
interior view of the eye
This unit holds a series of trial lenses that with a specific cylinder set are mounted on a wheel to accommodate any prescription up to and including +/- 30 diopters and usually +/- 6 diopters of cylinder
visual acuity refinement/Rx
used to give a baseline setting for the phoropter
will give a baseline k reading for the fitting of contact lenses