Several different tests are required for a complete assessment of the vision problem because of cataracts. It is possible that poor vision is merely because your prescription for glasses has changed. If attempts to improve the vision by changing the eyeglass prescription fails then the tests mentioned below will be needed to understand the reasons for your poor vision.

Refraction

Slitlamp exam

Dilated Fundus Exam

Keratometry

A-Scan

Visual Acuity Test
Best spectacle refraction is determined and then a vision chart is used to determine the visual acuity (see the online vision chart). Best spectacle corrected visual acuity worse than 20/40 is generally accepted to represent the visual acuity level at which cataract surgery may be reasonably considered with currently available small incision cataract surgery procedure. This level (vision = 20/40) represents approximately 20% reduction in visual efficiency. However, it is becoming increasingly clear that the deficits in a person's functional status, whether involving mobility, face recognition, or performance of various motor tasks cannot be confidently predicted from his or her visual acuity alone. From the published relationships between visual acuity and functional abilities, it might be predicted that an individual with reduced visual acuity would have certain deficits in functional abilities. For example, with vision worse than 20/40 a person is expected to have driving difficulties. Overall functional disability depends not only on the extent of deficits at specific tasks, but also on the relative importance that each of those tasks has in the individual's regular day-to-day activities. Therefore in some patients, even if the vision does not seem that bad on the vision chart, the functional disability may still interfere with the individual's lifestyle and cataract surgery may be considered if the risks of the procedure are acceptable. The reason why visual acuity alone may not adequately represent a patient's functional disability is that with cataracts other parameters that are important for good vision are also effected. These are: 1) Deficits in contrast sensitivity; and 2) Glare disability. Therefore if despite good visual acuity measurement on the vision chart you feel your vision quality is not good, then additional testing as described below is warranted.

Contrast Sensitivity Test
Vision is generally measured using an eye chart which has high-contrast letters; however, the world is almost never seen in such high contrast. The standard high-contrast visual acuity chart measures the ability to see black letters (about 1 or 2 percent reflectance) on a white background (close to 100 percent reflectance) giving close to 100 percent contrast. The real world, however, is far from this ideal. It consists of objects with an average reflectance of only 18 percent, and the contrast between objects of interest and their backgrounds is usually much less than 100 percent. For example, the contrast between the pavement and the sidewalk, which is the main cue that defines the edge of a curb, may typically be just a few percent.
Contrast provides critical information about edges, borders, and variations in brightness. People with poor contrast sensitivity fail to see large, low-contrast objects under conditions of poor visibility (such as fog) despite normal or near normal visual acuity. The importance of measuring contrast sensitivity is that it can provide information that cannot be obtained from visual acuity measures, and it is often a better predictor of performance than visual acuity.

The Pelli-Robson test measures contrast sensitivity using a single large letter size (20/60 optotype), with contrast varying across groups of letters. Specifically, the chart uses letters (6 per line), arranged in groups whose contrast varies from high to low. Patients read the letters, starting with the highest contrast, until they are unable to read two or three letters in a single group. Each group has three letters of the same contrast level, so there are three trials per contrast level. The subject is assigned a score based on the contrast of the last group in which two or three letters were correctly read. The score, a single number, is a measure of the subject's log contrast sensitivity. Thus a score of 2 means that the subject was able to read at least two of the three letters with a contrast of 1 percent (contrast sensitivity = 100 percent or log 2). A Pelli-Robson score of 2.0 indicates normal contrast sensitivity of 100 percent. Scores less than 2.0 signify poorer contrast sensitivity. Pelli-Robson contrast sensitivity score of less than 1.5 is consistent with visual impairment and a score of less than 1.0 represents in visual disability. This score (1.0) represents an approximately 10-fold loss of contrast sensitivity. That is, a person with contrast senstivity of 1.0 requires 10 times as much contrast to see as compared with a person with normal vision. A loss of this magnitude would be quite disabling and will have a huge impact on one's ability to drive or read.
Poor contrast sensitivity adversely effects the ability to read text, for example reading a newspaper. A contrast sensitivity of 1.0 or better is required to read high-contrast print at a normal speed. Most people with a contrast sensitivity of 1.0 or less will read text slowly. This level of contrast sensitivity is disabling with regard to walking speed. A person with contrast senstivity less than 1.3 will have difficulty in identifying the faces of individuals from a distance and will have an increased likelihood of automobile accidents. While performing typical manual tasks (e.g., sewing with a dark thread on dark cloth, doing woodwork etc) the contrast between different crucial parts of the task materials can be very low. It is likely that if one's ability to see under such reduced contrast is impaired, then their ability to perform these tasks will also be adversely affected.  
Bailey-Lovie chart may also be used to measure contrast sensitivity. In this chart all letters have the same contrast but their size varies (as in visual acuity charts).
The Vistech 'Vision Contrast Test System' (VCTS) presents a series of sine-wave gratings at different levels of contrast. Each row or circular grouping of patches tests at a specific spatial frequency (cycles per degree), which measures the observer's sensitivity to a particular object size. The low frequencies test sensitivity to very large objects while, on the other end, high frequencies measure sensitivity to very small objects. Each test frequency begins with a high level of contrast which diminishes progressively with each succeeding patch. The sine-waves, which appear as fuzzy gray bars, vary in their orientation within the patch and may be vertical or tilted left or right. The observer simply reports the lowest contrast patch visible in each grouping and describes the orientation. The tester records the results to produce a contrast sensitivity function, or curve. The curve is then compared to a population norm, and can be converted to a standard visual acuity value that relates to everyday functional vision. The instruction manual for VCTS is available here.
(Reference: National Research Council (2002) Visual Impairment: Determining Eligibility for Social Security Benefits. Committee on Disability Determination for Individuals with Visual Impairments. Peter Lennie and Susan B. Van Hemel, editors. Division of Behavioral and Social Sciences and Education. Washington, DC: National Academy Press)

Glare Disability Test
Many people with cataracts and other eye opacities are visually disabled in bright light conditions from scattering of light within the eye, that is referred to as glare. Measurement of visual function in the clinic or the laboratory is usually performed under ideal conditions of daytime ("photopic") lighting and the absence of extraneous light sources. Recommended lighting for acuity testing is on the order of 160 cd/m2. In the real world, however, levels encountered in bright sunlight can be up to 400 times greater than this, and in night driving typically 500 times dimmer. Strong extraneous light sources such as oncoming headlights or a bright sky often surround a visual target, creating glare problems. Glare disability is a reduction of the contrast of the retinal image caused by extraneous bright light sources present in the visual field. People with conditions that increase light scatter within the eye experience exaggerated impairments under conditions of glare. Glare resulting from light scatter may be due to optical irregularities within the eye, such as cataract. Glare may also originate external to the eye, such as because of scatter from airborne particles or irregularities on transparent surfaces, such as windows and spectacle lenses.
Brightness Acuity Tester (BAT) is used to test glare disability. The Brightness Acuity Tester can simulate three bright light conditions: 1) Direct overhead sunlight; 2) Partly cloudy day; 3) Bright overhead commercial lighting. The vision is measures using the low, medium or high light settings of the BAT. If the vision falls with light then the patient is deemed to have glare disability. The instruction manual for BAT is available here. Conditions of glare and low lighting arise in the course of many workplace tasks (e.g., driving, construction work, computer use). Strong extraneous light sources such as oncoming headlights or a bright sky often surround a visual target, creating glare problems. In addition to the cataract causing glare, light scatter from airborne particles or irregularities on otherwise transparent surfaces, such as windows and spectacle lenses may also contribute to glare. The impact of glare depends on the demands of the visual task. For example, when looking at a person silhouetted against a window or a very bright sky, contrast reduction can make it difficult to discern features in the face. In driving, detecting pedestrians, the edge of the roadway, or reading signs against a bright sky, sun, or headlights is likely to be difficult if ability to see in the presence of glare is impaired. Disability glare has been associated with the occurrence of motor vehicle collisions.

Potential Acuity Meter
The main purpose of performing this test is to get an idea of the visual acuity that the patient can potentially achieve. Prior to committing to cataract surgery it helps to know that vision improvement is possible (meaning there are no retinal or neurological issues that will not allow vision improvement despite cataract removal). The instruction manual for PAM is available here. An illuminated near card may be used to generate similar data.

Eye drops that are used to dilate pupil are: Phenylepherine and/or Tropicamide. The pupil dilates in about 30 minutes and remains dilated for about 6 hours. In some patients dilatation may persist longer than 6 hours. The drug dapiprazole (Rev-Eyes) can be used to reverse the dilatation. It works well to reverse Phenylepherine induced dilatation (88% reversal at the end of 1 hour). Tropicamide induced dilatation reversal is much slower (38% at the end of 2 hours).

Contact Us Complete the form below to contact us. If you would like a reply, please include your name and email address.