This project focuses on the development and evaluation of new vision screening technology and interventions applicable to the pediatric age group. Vision assessment in this age group is problematic, and certain deficits, if not detected and corrected early enough, can lead to partial or total blindness before the usual school-age screenings and interventions occur.
To address these problems, we have been developing and evaluating photographic vision assessment systems for rapid screening in the pediatric clinic or in the field. Emphasis has been placed on reducing the expensive and complex camera and optical systems used for experimental photorefraction to a practical low-cost device. We now have a Polaroid version of our photorefractive screening device, which is particularly suited to detecting the all-important asymmetries in refractive states between the two eyes.
Our modified Polaroid camera-based photorefractive vision screener has been undergoing a large-scale clinical trial to examine its application for detecting potentially blinding vision impairments in the non-specialist (pediatric) clinic. The field trial was conducted in the pediatric clinics of the Kaiser Permanente hospitals in Sacramento and Walnut Creek, in collaboration with Drs. Edward Denz and Leslie Chan. Infants were being screened by pediatricians at the twelve-month immunization visit.
Over 1,000 subjects have been tested, and a large amount of clinical data has been generated. The information we have gained from this trial to date has allowed us to devise modifications to our previous approach based on real-world experience.
As a result of the trial data, we plan further technical changes to the inexpensive camera design, including better exposure control and modifications of certain other design parameters. We also plan to develop a modified protocol to be more optimal for slightly older toddlers, with increased emphasis on the early detection of strabismus and anisometropia, as the system appears better suited to this category of visual impairment than the detection of high myopia in infants.
Under funding from NIH and NSF, we have developed a new Macintosh-based Visual Evoked Potential (VEP) recording system. The laboratory of Dr. Norcia of our staff has pioneered various now widely adopted methods of early vision screening using VEPs, and the new system extends this work even further.
Using a sophisticated adaptive filtering technique developed by staff member Yu Tang, the new system is conservatively estimated to give a 6 db improvement in signal-to-noise ratio, along with concomitant improvements in flexibility and speed. Vision of infants considered to be at risk for visual impairment can now be objectively measured on the new system with only a few seconds of attention span required. The system can also deal with much more complex stimuli for more sophisticated testing.
The new VEP recording system has already been adopted in ten other outside laboratories, confirming the perception that it represents an extremely valuable advance in infant vision screening and assessment for preventive rehabilitation.
We have developed a novel prototype nystagmus test for the early detection and quantification of disrupted binocular vision in persons with strabismus. The new test has several unique features including the ability to generate a sequence of simultaneous left- and right-traveling gratings, the intensity ratio of which can be adjusted to give quantitative readings.
In collaboration with Dr. Davida Teller of the University of Washington, Drs. Norcia and McKee of our laboratories conducted tests using a computer video-generated version of the new test, while simultaneously making eye movement recordings and measuring Visual Evoked Potentials (VEPs). The initial patient testing indicated that the new nystagmus test is based on sound conceptual principles and shows promise for clinical applications in preventative rehabilitation.
There is currently no standard practice for the pre-operative management of patients with infantile esotropia -- a common visual impairment in the pediatric population which, if not properly corrected, can lead to serious visual disability later in life. These infants develop strabismus before 6 months of age and require surgery between 9 months and 2 years of age. Arthur Jampolsky, M.D., has advocated the use of full-time, alternate-day occlusion during the period prior to surgery. Other practitioners use patching only to treat clinically apparent amblyopia. In this case the patch is placed part-time over the dominant eye.
In order to test a hypothesis on the efficacy of early intervention for "preventative rehabilitation," we followed a group of fourteen infants during the course of their pre-operative alternate occlusion therapy. We found that an index of abnormal binocularity -- asymmetrical monocular motion VEPs -- declined during the course of alternate occlusion. The index declined to a value less than that of untreated infantile esotropes of comparable ages. We concluded that alternate occlusion was causing a significant and presumably positive alteration in an otherwise pathological system. The pilot results suggest that alternate occlusion serves to disrupt an active, competitive interaction between the two eyes.
We are now organizing a randomized, prospective study of alternate occlusion therapy in a large group of infantile esotropia patients recruited from a number of different centers. This larger-scale trial, if successful, should produce sufficient evidence to allow this early intervention technique to be adopted as a standard preventive rehabilitation procedure.