At Vista Eye Centre, we offer state-of-the-art non-invasive diagnostic testing during the comprehensive eye examination, in preparation for laser, injection and surgical eye treatments, and to diagnose and monitor most eye conditions.
SLIT LAMP EXAMINATION
A slit lamp is a microscope mounted on a table which allows your ophthalmologist to examine your eye in order to determine your eye health and to detect disease. With the slit lamp, your ophthalmologist can look at specific structures at the front, middle and back of the eye.
The slit lamp exam is a routine part of every eye examination. No special preparation is needed. During the exam, your ophthalmologist will ask you to sit in the exam chair and put your chin in the chin rest and forehead against the forehead band. Your ophthalmologist may also place yellow (fluorescein drops) in the eye in order to highlight problems on the eye surface and to check your eye pressure with a Goldmann applanation tonometer (attached the to the slit lamp).
During the examination, your ophthalmologist will be able to assess different structures in the eye including: the conjunctiva, sclera, cornea, anterior chamber, iris, lens, vitreous, retina and optic nerve.
At Vista Eye Centre, we use the Haag Streit Slit Lamps for this examination.
Haag-Streit is the industry leader for this type of examination. The slit lamps in our practice provide unsurpassed accuracy, efficiency, while ensuring maximum patient comfort during the examination.
AUTO-REFRACTION AND KERATOMETRY
The autorefractor is an instrument used during an eye examination that provides an objective measurement of a person's refractive error and therefore determines if corrective lenses (glasses or contact lenses) will improve your vision. A keratometer measures the front curvature of your eye to detect astigmatism.
The autorefractor-keratometer is used during the comprehensive eye examination and at follow-up visits after cataract surgery. No preparation is needed. The ophthalmic technician will ask you to sit in an exam chair and to place your chin on the chin rest and forehead against the forehead bar. You will be asked to look at an image in the computerized machine. The computer will analyze how light rays are bent as then enter the eye (autorefraction) and the relationship between the size of an image shone on the surface of the eye and its reflected image. (keratometer).
At Vista eye center, we use the Nidek ARK1s Auto refractor/keratometer, which provides precise refraction measurements and also allows the technician to detect the patient’s quality of vision with a low contrast chart (manifest refraction). This information can help determine if a glasses prescription would improve the patient’s vision.
The measures the curve of your cornea to determine if you have astigmatism. Your eye doctor may also use corneal topography to evaluate astigmatism. Corneal topography provides more information about the shape of the surface of the cornea.
Corneal topography is an imaging test that maps the surface curvature or shape and power of the front of the eye or cornea. It is used to diagnose and measure corneal conditions and also for pre-cataract surgery assessment and post-cataract surgery investigations of the eye.
Corneal topography is done when your ophthalmologist suspects a corneal condition or in preparation for most cataract surgery. The cornea provides 70% of the eye’s refractive power, therefore corneal topography is an important measurement when calculating the power of the intraocular lens (IOL) to be used during cataract surgery. (This machine is also used to verify the position of a Toric IOL implanted during cataract surgery.)
Corneal topography is non-invasive picture of the eye performed by an ophthalmic technician. Your ophthalmologist will ask you to use artificial tear drops 3-4 X per day for 1-2 weeks before your corneal topography measurement. During the test, the ophthalmic technician will ask you to sit in an exam chair and to place your chin on the chin rest and forehead against the forehead bar. You will be asked to look at an image in the computerized machine.
At Vista eye centre, we use the NIDEK OPD III. The Nidek OPD-Scan III completes 20 diagnostic measurements in less than 10 seconds per eye by projecting a placido disc onto the cornea and providing a computer analysis of the reflected data points to produce an image of the corneal shape and power. The NidkeOPD also performs wavefront aberrometry providing additional data about the cornea: angle kappa, HOAs, average pupil power, RMS value, and point spread function).
NIDEK OPD-SCAN III FOR PRE-and POST- CATARACT SURGERY ASSESSMENT:
The OPD III provides comprehensive information for pre-operative assessment and post-operative investigations for cataract surgery. By using the Nidek OPD scan, we can determine if patients have dry eye or other corneal abnormalities prior to cataract surgery. If these are detected, the corneal surface can be optimized pre-operatively and the Nidek OPD scan can be repeated to increase accuracy of postoperative results.
Please use artificial tear drops 3-4 x per day for 1-2 weeks prior to coming to the office for a corneal topography scan in preparation for cataract surgery.
Additionally, the OPD-Scan III aids us in consulting our patients on the most appropriate intraocular lens (IOL) in each situation for best visual results after cataract surgery. Wavefront aberrometry measurements (pupillometry, angle kappa, spherical aberration and higher order aberrations) are an important part of IOL selection (especially for multifocal IOLs).
The OPD Scan is used for calculation of astigmatism correction and provides a Toric planning tool for Toric IOLs , which can be used to correct astigmatism during cataract surgery.
If a Toric IOL was implanted during cataract surgery, the Nidek OPDIII can be used to verify the Toric IOL position in the eye
VISUAL FIELD TESTING
Visual field testing is used to determine how wide an area your eye can see when you focus straight ahead. This test is used to diagnose and monitor eye conditions including glaucoma, problems with the optic nerve or retina.
A visual field test can help to map out blind spots (scotomas) in your vision. The location, size and shape of the blind spot can help to explain why your vision is blurred and if this is due glaucoma, optic nerve problems, retina problems or compression of the optic nerve in the brain (pituitary gland disorders or tumors) or other brain disorders (stroke). If you have glaucoma, the visual field test helps to make the diagnosis by mapping out peripheral vision loss, which can be tracked over time. If you have a central retina problem, the visual field test can help to diagnose and monitor the condition.
At Vista Eye Centre, we use an automated visual field machine for visual field testing, called the Humphrey® Field Analyzer 3 (HFA3). This is the gold standard in visual field testing. The HFA 3 reduces testing time with new algorithms (SITA™ Faster) and also provides progression analysis using mixed guided progression analysis (intermixing of SITA Standard, SITA Fast and SITA Faster). Central visual field testing is more accurately evaluated using new SITA Faster 24-2C, which adds additional test points in the central field.
No preparation is necessary for the test. This test is non-invasive. During the test, you will be asked to look into the center of a bowl-shaped instrument with one eye and the other eye will be covered with a patch. The eye being tested will have your lens prescription in front of it. It is important to keep your head still and to continue looking at the center target throughout the test. You will be asked to press a button when you see small brighter as well as dimmer lights in various sizes and in different places throughout the bowl. It is important to keep looking at the fixation light or center target throughout the test (even when you are seeing lights on the side) and to press the button when you see the light on the side. You can continue to blink normally throughout the test. The machine tracks which light you see and which ones you don’t see. The machine also monitors reliability of the test based on gaze, head tracking, and blind spot monitoring.
This test usually takes from 5-10 minutes to do but can take longer in some cases. If you are having problems doing the test, please let the ophthalmic technician know during the test or when you are finished.
IOL MASTER 700 and A SCAN
An A-scan ultrasound and IOL Master are used to provide accurate measurements for intraocular lens implants used in cataract surgery. The A scan uses ultrasonic waves to measure dimensions of the eye and to calculate the intraocular lens (IOL) power for cataract surgery, whereas the IOL master uses laser technology to measure the length and front curvature of the eye and to calculate the recommended intraocular (IOL) lens power.
IOL MASTER 700
At Vista Eye Centre, we use the IOL Master 700. This is latest technology and is more accurate than any other method that has been used in the past. This increased accuracy can reduce the need for glasses after cataract surgery. Additionally, the IOL master accurately predicts the specific IOL power required for each patient at the time of cataract surgery, in order to achieve the best possible vision postoperatively.
The Zeiss IOL Master 700 is a non-invasive test performed by an ophthalmic technician. Please use artificial tear drops 3-4 X per day for 1-2 weeks before this test. During the test, the ophthalmic technician will ask you to sit in an exam chair and to place your chin on the chin rest and forehead against the forehead bar. You will be asked to look at a fixation light in the IOL master.
The IOL master test takes 45-60 seconds and can measure through even very dense cataracts and corneal opacities (99% cataract penetration rate).
The IOL master 700 test is more accurate than other methods of measuring (axial) length of the eye because it uses swept source OCT images, (based on distance independent laser interferometry). In addition to measuring the length of the eye (axial length), the IOLMaster 700 also includes a unique telecentric (distance-independent) corneal measurement (keratometry) including a measurement of the posterior corneal surface.
Both axial lengths, keratometry and other precise eye measurements (anterior chamber depth, corneal central thickness and lens thickness), which are used to accurately predict the best intraocular lens for during cataract surgery. Various calculation methods are used, including the Barrett suite, integrating the newest IOL calculation formulas (Barrett Universal II, True-K and Toric), as well as the Holladay 1 and 2, SRK and Haigis calculation formulas allowing for improved accuracy in selection of IOL power and Toric IOL selection in preparation for cataract surgery.
The repeatability with the IOL master 700, is outstanding, improving expected outcomes after cataract surgery.
OCULAR COHERENCE TOMOGRAPHY (OCT)
Ocular coherence tomography (OCT) is an imaging test, which uses light waves to take cross-sectional pictures of the retina (with image resolution better than 10 microns) showing distinctive layers at the back of the eye, and helping to diagnose and manage conditions such as diabetic retinopathy, macular degeneration, uveitis, narrow angles and glaucoma.
The OCT is used as baseline testing during many comprehensive eye exams, and to fully evaluate patients with diabetic eye disease (diabetic retinopathy), macular degeneration (dry or wet), uveitis, central retinal (macular) abnormalities, narrow angles and glaucoma. The OCT is also used before and after cataract surgery in order to evaluate macular health.
No preparation is required for this test. This is a non-invasive test which takes 2-5 minutes to do. The ophthalmic technician will ask you to sit in a chair and to place your chin on the chin rest and forehead against the forehead bar. You will be asked to look at an image in the computerized machine. The OCT will shine a light in the eye and will create a series of images from the reflected light (from different structures in the eye) which are then analyzed using interferometry techniques. The ophthalmologist uses these two-and three-dimensional images (micrometer resolution) to diagnose and monitor eye conditions.
At Vista Eye centre, we use one of the newest models of OCT machines, the CIRRUS HD-OCT 5000, with improved resolution visualization capabilities and ability to evaluate and measure not only the retina but also the deeper layers including the retinal pigment epithelial and choroid. En Face views allow for layer by layer retinal analysis including the Vitreoretinal interface, mid-retina and photoreceptor (IS-OS or ellipsoid) views, which helps to diagnose epiretinal membranes, cystoid macular edema and hydrochloroquine toxicity, for example.
OCT is also used for optic nerve evaluation (in glaucoma or other optic nerve conditions), by measuring the retinal nerve fibers (retinal ganglion cell axons) as they approach the optic nerve (peripapillary region). Measurements used to evaluate glaucoma include disc and rim area, cup to disc ratio, cup volume. The enhanced Cirrhus 5000 HD-OCT also measures the retinal ganglion cells in the macula (center of the eye) as part of the glaucoma evaluation. The macula has the highest concentration of retinal ganglion cells in the retina and therefore glaucomatous loss may be detected in the macula before it is evident in the peripapillary region. By reviewing these various measurements, the ophthalmologist can determine the extent of structural damage in glaucoma.
Anterior segment imaging with the OCT
The Cirrus 5000 HD-OCT also includes a module which allows for full anterior chamber imaging and measurements, used for narrow angle and corneal thickness (pachymetry) measurements.
Anterior chamber measurements include a 15.5 mm wide view of the entire anterior chamber which includes tools for measuring anterior segment ocular structures , including the cornea thickness and irregularities in various locations (pachymetry map), anterior chamber angle (OCT goniometry, a non-contact method to help identify patients at risk of angle closure glaucoma) and detailed iridocorneal measurements to quantify and track degree of angle closure .
The new FastTrac™ retinal tracking included in all testing by the Cirrus 5000 HD-OCT reduces eye motion artifacts using high speed 20 Hz LSO camera, and single-pass alignment scanning. This feature enables the highest resolution images to be captured in identical locations from visit to visit providing precise assessment of change of any identified abnormalities.
Wide Angle-to-Angle scan and HD Angle Scan