Test Procedures

Color Test

The Farnsworth-Munsell 100 Hue and the Farnsworth Munsell D-15 tests consist of colored caps to be arranged in correct color order under controlled lighting conditions.

The D-15 test is used as a fast screening method for dichromatic type defects, while the 100 Hue gives more complete information of discrimination ability around the color chart.

The test administrator records chip arrangements on a standard sheet.

Dark Adaptation Test

The Dark Adaptation Test is a psychophysical test used to determine the ability of the rod photoreceptors to increase their sensitivity in the dark.

This test is a measure of the rate at which the rod and cone system recover sensitivity in the dark following exposure to a bright light source.

Fundus Photography

A fundus camera, or retinal camera, is a specialized low power microscope with an attached camera designed to photograph the interior surface of the eye, including:

  • Retina
  • Optic disc
  • Macula
  • Posterior pole (i.e. the fundus).

Fundus cameras are used by optometrists, ophthalmologists, and trained medical professionals for monitoring progression of an ocular disease, diagnosis of a disease, or in screening programs, where the photos can be analyzed later. Measuring the ratio of the optic cup, documenting a choroidal nevus, or tracking dry ARMD are some of the more common uses of fundus photography.

Fundus photography is also used in clinical trials in order to monitor the effect of new medications and also to have them approved by the FDA. 

Humphrey Visual Field

The primary function of the Humphrey visual field machine is to measure the patient’s peripheral and central vision with repeated light stimulus of varying intensities appearing in different parts of the field while the eye is focused on a central spot. The results are then compared with those of the age-matched normal population.

Visual field testing is performed for screening for glaucoma. Another function is to measure the severity of lid droop of ptosis of the eyelid. Testing for macular diseases such as macular degeneration or toxicity from certain medications such as Plaquenil used for rheumatoid arthritis. Testing can also be performed for the following:

  • The visual pathways to the brain,
  • The visual or occipital cortex and optic nerve looking for:
  • Tumors
  • Brain swelling injury
  • Poor circulation

A baseline test is performed with follow-up testing within  one to three months, six to 12 months, or yearly to compare results is advisable. 

IOL Master

The Zeiss IOL master is an optical device that measures the distance from the corneal vertex to the retinal pigment epithelium by partial coherence interferometry. The IOL master is the first such device to be widely used in clinical ophthalmology calibrated against the ultra-high resolution 40 mhz Grieshaber Biometric System.

The IOL Master allows fast, accurate measurements of the eye length and surface curvature necessary for cataract surgery, that is axial length, anterior chamber and width to width. And because the IOL Master is non-contact (nothing touches the eye itself), there is no need for anesthesia nor potential for spread if contamination from the IOL Master. The patient is seated comfortably and positioned in a chin rest similar to what is typically used for a slit lamp. The overview mode is used for course alignment; the patient looks at a small, yellow fixation light.

Clinical situations may interfere with the partially coherent light beams and decrease the sound/noise rate to the point that preclude a meaningful measurement. These situations include:

  • A mature or darkly brunescent lens
  • Central posterior subcapsular plaques
  • Anterior cortical spokes
  • Corneal scars that pass through the visual axis
  • Vitreous hemorrhages

In the typical ophthalmology practice, approximately 90% of patients can be measured successfully using the IOL Master. The remaining 10% of patients must be measured by A-scan ultrasonography for the reasons outlined above. 

Non-mydriatic Fundus Photography

A fundus camera, or retinal camera, is a specialized low-power microscope with an attached camera designed to photograph the interior surface of the eye, including:

  • Retina
  • Optic disc
  • Macula

Posterior pole (i.e. the fundus).

Fundus cameras are used by optometrists, ophthalmologists, and trained medical professionals for monitoring progression of an ocular disease, diagnosis of a disease, or in screening programs, where the photos can be analyzed later.

A non-mydriatic camera is useful for those patients who should not be dilated, like a patient with narrow angle glaucoma or papillary defects. There are occasions when a patient’s pupil just won’t dilate well and the mydriatic camera is unable to obtain as clear of a view of the fundus. 

Pentacam

The Pentacam is a diagnostic tool used to take measurements of the anterior segment of the eye. This device combines the use of the slit illumination system together with a rotational camera, called a Scheimpflug, to achieve a complete measurement and analysis of the center of the cornea. A thin layer of the eye is illuminated through the slit. The camera is oriented so that the image of the illuminated place appears distinct and sharp from the anterior surface of the cornea right up to the posterior surface of the crystalline lens. The slit-camera device rotates 360 degrees around the eye, generating a series of radially oriented images that combine to create a three-dimensional model of the entire eye chamber.

Eye movements during image acquisition are captured by a second camera, known as the pupil camera, and taken into account in the mathematical evaluation. This produces a set of three-dimensional measurement data which gives a precise geometric description of the anterior eye segment. This data in turn can be used to generate data on elevation, curvature, pachymetry, depth of the anterior chamber and more...

The Pentacam is used to evaluate potential patients for Lasik, cataract, glaucoma surgery and corneal transplants among other procedures. Also, it is a tool used by an eye doctor to determine if a patient is a candidate for a refractive eye surgery by screening for kerataconus. 

Ret Cam Shuttle

The Ret Cam is a mobile, wide-field digital imaging system that specializes in ophthalmic imaging. It contains a variety of lenses that are used to document the optic nerve, the retina, the cornea, and the external view of the eye at a number of magnifications.

The Ret Cam has the same functionality as the fundus camera that is currently used in the office. However, the Ret Cam takes things a step further. This system can be taken to outside offices and hospitals, especially to document those patients who have been admitted into the hospital. It can be used right at their bedside.

The Ret Cam proves to be very helpful in the operating room, as well. It gives Wills Eye the capability of imaging those patients whom we cannot document in the office, such as young children who need to be under anesthesia. It also gives Wills Eye the means to obtain pre and post operative photographs for the doctor to read instantaneously while still with the patient.

The Ret Cam also specializes in the imaging of babies outside of the operating room. It can be difficult to obtain a clear view in the eye of a child since they may have a hard time keeping their eyes or even themselves in one position. The Ret Cam has a video feature verses still imagery, which gives us more versatility in circumstances where the child is in the office and not under anesthesia.

Altogether, the Ret Cam proves to be a valuable tool in the documentation, the diagnosis, and the treatment of ophthalmic diseases. 

Slit Lamp Camera

The slit lamp camera is an instrument that consists of a high-intensity light source that can be focused to shine a thin sheet of light into the eye. It is used in conjunction with a biomicroscope.

The lamp facilitates an examination of the anterior segment, or frontal structures of the human eye, which includes:

  • Eyelid
  • Sclera
  • Conjunctiva
  • Iris
  • Lens
  • Cornea

The binocular slit-lamp examination provides a stereoscopic magnified view of the eye structures in detail, enabling anatomical diagnosis to be made for a variety of eye conditions.

The slit beam serves as a great tool for documentation and can be manipulated to obtain a multitude of visual effects, which can illuminate the area of interest. This can help to dictate the severity of a disease, like how many layers a mass may be penetrating through, how narrow the anterior chamber angle is, or how dense a cataract is.

Visual Evoked Respons​e

This test measure how long takes the signal to go from the optic nerve to the visual center of the brain (located in the back of the head).

Visual evoked response (VER) is an objective test of cortical visual activity. An electrode is placed on the inion to record a mass electrical signal from cells in the visual cortex. A positive result from this test depends upon the adequate functioning of the afferent visual pathway from the retina to the brain.

Electroretinogram

This test checks the electrical activity of the retina. Electroretinogram (Erg) is an objective test of the electrical function of the retina. Contact lens electrodes placed on the cornea allow recording of a complex electrical response from the entire retina to appropriate light stimulation. Dim lights test the rod responses and the brighter lights test the cone responses.

Multifocal Electroretinography

This test stimulates all different parts of the retina. Multifocal Electroretinography (MFERG) records complex electrical response from individual areas of the retina to standardized stimuli. Provides objective information about retinal function of the cone systems. Individual ERG waveforms are mapped out in the report.

Electrooculography

The eye acts as a dipole in which the anterior pole is positive and the posterior pole is negative.
Left Gaze: the cornea approaches the electrode near the outer canthus resulting in a positive-going change in the potential difference recorded from it.

Right Gaze: the cornea approaches the electrode near the inner canthus resulting in a positive-going change in the potential difference recorded from it (A, an AC/DC amplifier).

 

Ophthalmological Diagnosis

 

The EOG is used to assess the function of the pigment epithelium. During dark adaptation, the resting potential decreases slightly and reaches a minimum ("dark trough") after several minutes. When the light is switched on, a substantial increase of the resting potential occurs ("light peak"), which drops off after a few minutes when the retina adapts to the light. The ratio of the voltages (i.e. light peak divided by dark trough) is known as the Arden ratio. In practice, the measurement is similar to the eye movement recordings. The patient is asked to switch the eye position repeatedly between two points (usually to the left and right of the center). Since these positions are constant, a change in the recorded potential originates from a change in the resting potential.