16 however, found that contrast sensitivity scores were lower for all patients with lens opacities than for clear lenses at high frequencies only, and all lens opacity groups scored similarly with each other. This loss was also correlated with decreased Snellen visual acuity. 15 found significant contrast sensitivity loss only in advanced cortical and posterior subcapsular cataracts. 14 documented correlations between early nuclear cataracts with loss of contrast sensitivity in the intermediate and high spatial frequencies (4 to 16 cycles per degree). They suggested that early cataracts cause high-spatial frequency loss, whereas more advanced cataracts produce both high- and low-spatial frequency losses. Hess and Woo 13 first reported contrast sensitivity function loss in patients with cataracts. The second type of devices are based on photographically reproduced sine wave gratings (such as the Arden plates and the Vistech vision contrast test system) or variable contrast optic types (such as the Regan letter chart, the Vistest picture test, the Pelli-Robson letter chart, and the Melbourne edge test), 12
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11 Examples of this are, among others, Optec 3500 Vision Tester (Stereo Optical Co., Inc., Chicago, IL), B-VAT PC system (Medtronic Solan Co., Inc., Jacksonville, FL), Smart System 20/20 (M & S Technologies, Inc., Chicago, IL), and CSV-1000E Contrast Sensitivity Instrument (VectorVision, Inc., Arcanum, OH). 10 The traditional devices consist of sine wave gratings, which are patterns of alternating light and dark bars produced and controlled by computers, wherein the spatial frequency, contrast luminance, field size, and attenuation at the edge of the field are either modifiable or fixed. In general there are two types of devices used for contrast sensitivity testing. Cataracts increase intraocular light scatter causing a reduction in retinal image contrast, and a subsequent decrease in contrast sensitivity. Hence, the cataract needed to be removed to allow the patient to continue driving.Ĭontrast sensitivity is a measure of the amount of contrast required to detect or recognize the target.
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In most states, a minimum requirement for an unrestricted license to drive a vehicle was a visual acuity of 20/40 and a patient could potentially lose his/her driver’s license should his/her Snellen acuity drop below this level. With the development of safer techniques such as the intracapsular cataract extraction (ICCE) technique using the Cryoprobe, and later the extracapsular cataract extraction (ECCE) technique using automated irrigation-aspiration (I/A) devices and implantation of an intraocular lens (IOL), the indication for cataract surgery was lowered to a Snellen acuity of 20/40 or worse coupled with anticipated improvement of vision. Patients were advised to wait until their cataract was “ripe” and their Snellen visual acuity dropped down to 20/80 or worse before contemplating surgery. Magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) spectroscopyĪs recently as four decades ago, as a result of high complication rates, cataract surgery was deferred until a patient did not have much to lose in terms of visual acuity, should intraoperative or postoperative surgical complications occur.Quasielastic or dynamic light scattering (QELS or DLS).Others: Laser slit lamp, sequential color imaging and analysis.Retroillumination imaging and area analysis systems.Scheimpflug slit lamp imaging and densitometry systems.Specialized slit-lamp photography/imaging.Other systems such as the Japanese CCRG Cataract Grading system and the World Health Organization Cataract Grading System.Age-Related Eye Disease Study (AREDS) Cataract Grading System.Oxford Clinical Cataract Grading system.Wilmer Clinical and Photographic Cataract Grading system.Wisconsin Clinical and Photographic Cataract Grading system.Lens Opacities Classification System (LOCS) III Clinical and Photographic Grading system.
Standardized clinical grading and photographic systems (comparing a patient’s cataract with standard photographs).Clinical examination with hand-held light, slit-lamp biomicroscopy and ophthalmoscopy and accessory devices.Clinical examination and documentation of physical lens changes.Others: Short Form 36 (SF-36), Activities of Daily Vision (ADV), Sickness Impact Profile.Functional Impairment/Quality-of life tests.
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