Vision Science Labs- Vision Assessments

General Vision Assessments (No hardware required)

• Visual Acuity measures the clarity of vision for an individual. Myriad eye diseases negatively affect visual clarity including: Cataracts, Dry Eye, Refractive status (hyperopia, myopia, astigmatism), Macular Degeneration, changes in ocular vascular perfusion which can stem from Diabetes, Glaucoma, venous and arterial occlusion and others.
• Visual Field used to assess the sensitivity of central and peripheral vision monocularly. Can help localize brain lesions, detect stroke or intracranial pathology, screen for visual changes due to potentially damaging medications, frequently used to monitor glaucoma patients who have a tendency to progressively lose peripheral vision sensitivity.
• Amsler Grid assesses the macular contour. For a healthy individual the macula has a smooth dip and provides what we think of as normal vision. If pathology disrupts this contour it can cause visual space to be distorted, making the lines on the Amsler grid appear wavy. Diseases that can disrupt the macular contour include Macular Degeneration, Diabetes (macular edema), Epiretinal membrane, Central Serous retinopathy, retinopathy stemming from medications (e.g. Chloroquine, Hydroxychloroquine)
• Accommodation is characterized by the crystalline lenses ability to change shape. This gives us the ability to change focusing distances. Accommodation has only two overarching ways in which at can be tested. Change the distance between an observer and an object of interest (closer increases accommodative demand), or change lens power (more negative lens powers increase accommodative demand). Testing this would allow for detection of Presbyopia and accommodative conditions such as Accommodative Insufficiency, Infacility, and Excess.
• Tracking - There are two macro types of eye movements (there are some academically relevant micro eye movements but with minimal clinical value at this time) pursuits and saccades. Tracking seems more consistent to me with pursuit eye movements that are employed when someone is tracking a fly ball at a baseball game for instance. Pursuit movements can decline in conjunction with cognitive deterioration. Also in various positions of gaze pursuits can breakdown and result in nystagmus (this can be a giveaway during roadside sobriety testing). Diplopia (double vision) can also emerge during pursuit testing which may prompt further binocular and neurological investigation.
• OKN Drum tests for the optokinetic reflex. This reflex occurs when following a quickly moving object, for instance when looking out the window of a car and you can’t quite keep up with the moving scenery so your eyes jump back to a more straight ahead positioning. The OKN drum creates the same response and can be used as a measure of visual acuity for visually impaired individuals and is sometimes used in assessing visual acuity for infants.
• Contrast Sensitivity is the ability to detect slight changes in the foreground relative to the background. This skill can be tested by measuring the threshold in detecting letters or shading with decreasing levels of darkness, e.g. going from completely black lettering to nearly white. This test can assist in following the progression of macular degeneration and cataracts, and is often tested for athletes in sports vision assessments.

Binocular or Oculomotor Assessments (Most require red-blue 3D glasses)

• Stereo Acuity is an assessment of depth perception. Typically in clinic we don’t test to the very threshold of human capability, but you could do this if testing athletes for a sports vision assessment. Stereo acuity also gives us insight into the binocular development for patients, as binocular vision is necessary for appreciating depth, and if a patient did not achieve binocular fixation during development it is unlikely they will have a significant degree, or any, stereo acuity.
• Cover Test measures the resting position or phoria of the eyes, can be exo (eyes aimed further away than the target), eso (eyes aimed nearer than the target) or ortho (eye in alignment with the target). This test is typically done at near and far and can help to diagnose binocular conditions such as convergence insufficiency, or convergence excess (also divergence misalignments as well) in conjunction with vergence testing and near point of convergence (NPC) testing.
• Fixation Disparity this is a rather subtle measurement and a bit complicated and academic. Basically, the test assesses the degree of misalignment in space between where an individual is looking and where an object is located. This is for a fused object (meaning binocular fusion is intact as opposed to the cover test where fusion is broken). Mostly done for research purposes, or sometimes for prescribing prism in glasses.
• Fusional Vergences assess the eyes ability to maintain binocular fixation. Both the ability to converge (crossing the eyes) and diverging (making the eyes go closer to parallel) can be measured. Used for determining binocular conditions as mentioned in the cover test section. Also called vergence ranges.
• Worth Four Dot relatively simple way of assessing binocular vision, often done for younger patients. Test is conducted using red/green glasses (classically, could use red, blue). Can be used to determine if patient is achieving binocular fixation, or is suppressing (shutting of one eye) or has a tropia (misalignment of the eyes) causing diplopia (double vision).