Models of the Visual System, George K. Hung and Kenneth J. Ciuffreda, eds. New York: New York: Kluwer Academic/Plenum Publishers, 2002. Pages: 781. Price: $115.00. ISBN 0-306-46715-1. When I agreed to review this book, I thought, “what a great chance to review and improve my knowledge about how the eye works.” I hadn’t had a chance to do that since graduate school. When the book arrived, its girth and the mathematical modeling symbols on the cover made me afraid of having made one of my typical mistakes of letting my wishful thinking get the best of my good judgment. However, I jumped right into the review of this massive text (781 pages) with the idea of looking it over and then delving into the section that I knew the most about (oculomotor function). However, I did not make it to the oculomotor section of the book right away, as I planned, because I was enticed to do much more than just get a quick overview of each section. I found myself drawn into each section of the book (there are 5 sections) with remarkable strength. In retrospect, I think that is because the authors of each chapter must have anticipated, that to interest the reader, they must “hook” him. They did this by first doing a nice summary of how they organized the chapter and clearly spelled out what they had to offer the reader. Well, I’ll be darned if they didn’t get me every time. I found myself intrigued with things like the model of the aging of the crystalline lens, a topic that I confess I would have, most likely, avoided in another publication. I was drawn in partly by the reader-friendly organization of the material. Each chapter starts with a review to make the reader comfortable, and I found myself saying, “I should read this over just to see what I remember.” This was usually followed by questions about the function of the part of the eye with which the chapter dealt, and I found myself thinking, “Oh, this should be good.” Well, it was. Time after time I found myself feeling good about the time it took to read and consider what the authors had to say. Now don’t get me wrong. most of this book is not read lightly, and sooner or later I found myself thinking, “I’m lost, I will have to read over this again more deeply.” But I found that the interest created was long lasting, and I did go back and try to understand better what I missed the first time. I was not always successful; however a useful text is not one that is mastered in a first read but one that will last and challenge for years to come and perhaps draw us into areas we had not yet considered. The book is organized into five sections: (1) optical systems: cornea and lens; (2) neurosensory systems: retina and visual cortex; (3) oculomotor systems: accommodation, vergence, and eye tracking; (4) perceptual systems: texture, motion, visual attention, and cognitive processing; and (5) clinical systems: refractive error development, clinical vergence testing, reading disability, and nystagmus. I was a little disappointed in the quality of the pictures in the text: all were black and white images. Such images are okay for graphical figures and models, but leaves something to be desired in the pictures. As the editors mention, the book is aimed first toward college seniors and beginning graduate students in biomedical engineering, neurophysiology, optometry, and psychology. It is definitely not just limited to those groups, because it has considerable depth in some areas, and presents important new material in each area to be useful as a reference work for graduate students and post-doctoral fellows as well as interested clinical optometrists and vision scientists. Students need this book to help them understand how the eye works. Clinicians will find the oculomotor and clinical systems sections alone worth the investment. They will be surprised how much else they learn about ocular function on their way to reading what they thought they were most interested in. Vision scientists are always looking for fresh approaches to their areas of interest. The modeling efforts of some very good scientists and their unique attack of important ocular problems show us different strategies at work. FIGUREFigure

BACKGROUND:Standard accommodative facility testing, using +/- 2.00 D lenses @ 40 cm, stresses a much different proportion of the available accommodation for a 10-year-old patient with a binocular accommodative amplitude of 12 D and a 35-year-old patient with a binocular amplitude of 5 D. This may explain why research using adult subjects has failed to associate reduced accommodative facility with symptoms.METHODS:For 19 adult subjects with normal age-related amplitudes of accommodation, accommodative facility was measured with the standard test (+/- 2.00 D @ 40 cm) and 36 experimental combinations of test distance demand and lens power range, based on percentages of each individual's amplitude. In a masked study. these results were compared to symptom scores, quantified by a 9-item quality of vision questionnaire.RESULTS:The strongest relation of facility with symptoms was for the 75% distance demand/30% power range (p = 0.0216), with six other combinations also significant. The standard test combination did not significantly differentiate symptomatic from asymptomatic subjects (p = 0.1 515). The combination of the 45% distance demand/30% power range was significantly related to symptom score (p = 0.0315; r = -0.47603).CONCLUSION:Amplitude scaled facility testing provides the same percentage test distance and range of amplitude stimulated for all patients. The 45%/30% test combination differentiates symptomatic from asymptomatic subjects better than the standard test (+/- 2.00 D @ 40 cm) and is the one we suggest for future clinical investigation. Care should be taken when testing symptomatic patients over a long period of time, as they may compensate by relying on a predictor operator during the highly repetitive accommodative facility test, thus achieving a more-rapid response.

Saturday, December 14, 2002: Posters: Binocular Vision, Pediatric Optometry, Public Health, Vision Science: PDF Only

BACKGROUND:Accommodative facility testing is used in clinical care to assess functioning of the ocular accommodative system. The current clinical standard (binocular assessment using +/- 2.00 D lenses at 40 cm with a vectographic suppression check) was first described nearly 20 years ago as part of the last comprehensive review of the literature. The standard accommodative facility test imposes a variable requirement on patients of different ages who have a wide range of accommodative amplitudes.METHOD:In this article, we critically reviewthe present body of literature on accommodative facility testing, with emphasis on the relation between symptoms, accommodative amplitude, and the results found during accommodative facility testing.RESULT:We include discussion of the five broad categories of accommodative facility studies: (11 recommendations for testing criteria; (2) normative data investigations; (3) reliability and variability assessment; (4) relation between accommodative facility and symptoms; and (5) other relationships (e.g., effect of test parameters on accommodative facility).CONCLUSION:Given the substantial variation in demand when testing patients of different ages (amplitudes), it is not surprising that a significant variation in responses has been reported in the clinical accommodative facility literature. Future clinical investigation of accommodative facility would benefit from a systematic investigation into the relationship between age and amplitude. The presence or absence of symptoms needs to be considered so that results of testing can be analyzed in relation to the severity of binocular vision-related symptoms.

Morse, Stephen E. OD, PhD; Woodbury, Michelle OTR/L, MA; Hoxie, Judy COT, MA Author Information

Night myopia is the increase in ocular refraction occurring in low levels of illumination. Although night myopia has been known for centuries, there is still no effective method for prescribing the optimal lens to correct the condition. One difficulty is that the tendency of accommodation to seek its dark focus at low luminance may be opposed by convergence. For example, if there is enough luminance to sustain binocular vision, accommodation is influenced by fusional vergence. Therefore, the best optical compensation for night myopia should depend not only on the dark focus of accommodation, but also on the influence that vergence has on accommodation. The degree to which fusional vergence influences accommodation is known as the convergence accommodation to convergence (CA/C) ratio. Our PURPOSE was to perform an experiment under realistic night myopia conditions (binocular viewing and natural pupils) which would allow us to relate the power of the best optical correction to individual differences in the dark focus of accommodation and CA/C ratio. METHODS. The optimal optical compensation for night myopia was determined by measuring visual acuity under binocular conditions across three luminances (0.04, 0.4, and 4.0 cd/m2) and four lens powers (0.0, -0.5, -1.0, and -1.5 diopters). The dark focus was measured with an infrared optometer, and CA/C ratio was measured with an infrared optometer and eyetracker. Sixteen subjects (mean age 25.4 years) with unaided visual acuity of 20/20 were tested. RESULTS. Regardless of CA/C ratio, the optimal lens power was significantly correlated with dark focus. However, the slope of the regression line relating lens power to dark focus was much steeper for subjects with low CA/C ratios than with high ones. CONCLUSIONS. It appears that variability in night myopia can be explained by intersubject differences in dark focus and CA/C ratio. We found that a lens equal to approximately the full dark focus value optimized vision in subjects with low CA/C ratios, and that a one-half dark focus correction did the same for subjects with high CA/C ratios. In addition, we also found evidence for a previously unknown natural mechanism that appears to limit the amount of night myopia through a non-random association of dark focus and CA/C. This process we termed “night emmetropization” because it appears to result in less night myopia than would be expected if there were only a chance association between CA/C and dark focus.

1College of Optometry, University of Houston, Houston, TX; 2U.S.Army Aeromedical Research Laboratory, Ft. Rucker, AL.

: Many factors which could affect visual acuity (VA) with night vision goggles (NVGs) already have been studied, e.g., night sky condition and target contrast (Levine and Rash, 1989a and 1989b; Wiley, 1989; Kotulak and Rash, 1992) , NVG generation (Miller et al., 1984; Kotulak and Rash, 1992), nuclear flashblindness protection (Levine and Rash, 1989a and 1989b), chemical protective masks (Miller et al., 1989; Donohue-Perry, Riegler, and Hausman, 1990), signal-to-noise ratio (Riegler et al., 1991), interpupillary distance misadjustment (King and morse, 1992), and instrument myopia (Kotulak and Morse, 1992, 1994a, and 1994b; Kotulak, Morse, and Wiley, 1993). Another factor which could influence NVG VA is decreased unaided VA, i.e., VA without NVGs; however, relatively little is known about it.

Morse, Stephen E. OD, PhD; Kotulak, John C. OD, MS; Rabin, Jeffrey C. OD, PhD Author Information

: Emmetropic subjects focus optical instruments as though they were myopic when the level of accommodation with instrument viewing is no greater than it is without.