Contrast Sensitivity: Adding SPARCS to Your Testing

Mr. X – a patient on a fixed-dose prostaglandin with timolol combination for advanced glaucomatous optic neuropathy – visited his doctor. He was finding it increasingly difficult to adjust after entering a room after his daytime stroll. His evening stroll had taken a toll as well because he wasn’t able to see the curb at the roadside.

A junior fellow addressed his concerns: “You already have advanced visual field defects – a repeat test would be non-contributory. Also, because your intraocular pressures (IOPs) are in the early teens, it is unlikely that the disease is progressing.” But then Dr. Y comes in, listens to Mr. X’s concerns, and orders a test to assess contrast sensitivity (CS).

Mr. X had already performed this new web-based, online test – known as SPARCS (Spaeth Richman Contrast Sensitivity) test* – a few months back. The repeat SPARCS test showed that there was a decline in the central score as well as peripheral scores in two quadrants, suggesting progressive functional deterioration. Dr. Y stepped up the therapy and suggested some changes to help improve contrast in the home environment.

This case scenario highlights the need not only to listen to our patients’ concerns regarding a very important visual function, but also to use appropriate tools to quantify it and then use the results for clinical decision making. Unlike standard visual acuity tests, which assess the ability to see black letters on a white background, CS testing evaluates visual function in more real-world scenarios. CS is important for tasks such as reading, driving, and recognizing objects in various lighting conditions. CS decline occurs in several ophthalmic disorders including cataract, glaucoma, diabetic retinopathy, and age related macular degeneration (1).

Choosing the best CS test or stimulus to be used in a clinical practice is a topic of debate. Letter-based CS charts measure recognition, while gratings refer to a detection task. The advantages of SPARCS over letter-based CS charts, such as the Pelli Robson chart, is that SPARCS is independent of the effects of literacy and language, chart fading, inadequate illumination, reflections, and limited optotypes. SPARCS can also be performed on most freely available web browsers, such as Chrome and Firefox – an added bonus given that most CS tests are not sufficiently accessible geographically, economically, or psychologically.

SPARCS also ascertains both central as well as peripheral CS, bridging a critical gap in current CS evaluation techniques. Studies using SPARCS have shown that CS correlates with quality of life and people’s actual ability to perform activities of daily living better than visual field, visual acuity, stereopsis, and IOP (2).

Dr. Y also showed the patient that SPARCS can be administered by anyone with a minimum of training; indeed, it is designed to permit self-testing by anyone who has access to a web browser. Vertical contrast bars of varying levels of contrast are randomly shown in five distinct areas of the field of vision – centrally, upper right, upper left, lower right, and lower left. The patient is instructed to click the area where the contrast images were displayed. When the limits of the individual’s ability to see contrast are established, the score results are displayed for the patient, automatically stored in the patient’s record, and are immediately available for review by the patient’s doctor. The cumulative SPARCS score is the sum of all five areas, with 100 being the highest possible combined score. The data obtained by SPARCS is digital, quantitative, and immediately integrated into databases from which critical patterns, whether for individuals or populations, can be analyzed.

Given that classical glaucomatous visual field loss is usually detected first in the periphery (often as an arcuate scotoma occurring in the superior or inferior hemifield within 20 degrees of the fovea), researchers have attempted to correlate peripheral visual field loss with CS measurements. Glaucoma patients with even early optic nerve rim tissue loss, scored lower CS values than 95 percent of controls (3). And SPARCS scores were one of the best predictors when it came to identifying which glaucoma patients were at the highest risk of progressing rapidly (4). The potential of CS scores as markers to identify high-risk glaucoma patients needs to be explored. As in Mr. X’s case, when the glaucoma is very advanced, the floor effects in structural imaging often impede the accurate detection of progression; in such cases, SPARCS can save the day.

Elderly patients with glaucoma often have coexisting cataracts; for these patients SPARCS is also more adept at identifying decline in CS with increasing cataract severity (5).

CS loss is diffuse throughout the field of vision, unlike the clusters of function loss (scotoma) seen on visual field testing. Therefore, more research is needed to ascertain how CS reduction is associated with the progressive loss of neural tissue in specific areas of the retina.

Testing at a fixed, low-spatial frequency is a relative drawback of SPARCS, but even this low spatial frequency complements the Snellen visual acuity assessment.

As we advance in the field of ophthalmology, innovative tools such as SPARCS are poised to play a pivotal role in enhancing diagnostic and therapeutic approaches, thereby raising the bar for standards of patient care.

* SPARCS was invented by George L. Spaeth, Jesse Richman, and Eric Spaeth. Patent number 8,042,946. SPARCS is in the process of being adapted for licensed use.

^{Article image credit: The Ophthalmologist}