I was never any good at those search-and-find books as a kid. Where’s Waldo eluded me for years. As an adult, my own children have much more of a knack for it than I ever did (or do to this day). Should I be worried about my relatively poor performance at such games, or is this just me being me?
A 2019 study published in Investigative Ophthalmology and Visual Science examines a functional aspect of glaucomatous damage that deserves more attention than it currently receives.1
ODs learn of the crowding phenomenon when studying amblyopia in school (see Figure 1, to the bottom right). Testing visual acuity on amblyopic patients using crowded optotypes has been studied for years.2
However, visual crowding may also have implications for the functional assessment of glaucoma patients. The authors of this study tested 13 subjects with “mild glaucomatous visual field loss” and 13 controls.
Visual crowding was determined by having each subject determine the orientation of the letter “T” presented 10 degrees away from a fixation target in each quadrant. The optotype was crowded, or “flanked,” by two letter “Hs,” and the subjects were asked to determine whether the T was upright or downright during 12 testing blocks consisting of 50 trials a piece for a total of 600 trials.
Prior to the crowding trials, the researchers tested to see if the subjects could initially see the letter T in each quadrant in order to determine if anyone would perform poorly simply because the optotype was in an area of glaucomatous visual field loss.
In addition to standard visual field testing, dilated eye examinations and baseline optical coherence tomography (OCT) studies were obtained on each study participant in order to quantify glaucomatous damage and isolate confounding diseases or conditions that could also cause visual impairment.
Only patients with open angles by gonioscopy were included, and ocular hypertensives without evidence of glaucoma (defined in this study as two or more consecutive abnormal visual field studies and glaucomatous-appearing optic discs) were excluded.
1. Ogata NG, Boer ER, Daga FB, Jammal AA, Stringham JM, Medeiros FA. Visual crowding in glaucoma. Invest Ophthalmol Vis Sci. 2019 Feb 1;60(2):538-543.
2. Levi DM, Klein SA. Vernier acuity, crowding and amblyopia. Vision Res. 1985;25:979–991.
3. Pelli DG. Crowding: a cortical constraint on object recognition. Curr Opin Neurobiol. 2008 Aug;18(4):445–451