Evaluation of photoscreener instruments in a childhood population. 1. Otago photoscreener and Dortmans videophotorefractor

Wave-front analysis as screening technique for amblyogenic ametropia with and without cycloplegia

INTRODUCTION

For many years, attempts have been made to find an easy, efficient and inexpensive method to screen children for amblyogenic ametropia. Wave-front analysis is a new way to determine the refractive state of the eye from a distance. This technique could be a useful tool for infant screening.

PURPOSE

The purpose of the study was the evaluation of the efficacy of a commercially available wave-front analyzing autorefractometer (SureSight, software version 2.0, Welch Allyn, Skaneateles Falls, NY 13153, U.S.A.) in detecting amblyogenic ametropia in patients with and without cycloplegia.

METHODS

256 eyes (-28.25 D to +7.88 D spherical equivalent) of 128 patients (1-81 years) were examined with the wave-front autorefractometer under cycloplegia. Prior to this investigation, 108 eyes (-21.38 D to 75 D) of 54 of these patients (1-76 years) were refracted without cycloplegia. The readings of the wave-front autorefractometer were compared with the results of retinoscopy under cycloplegia.

RESULTS

Without cycloplegia, the sensitivity in detecting any amblyogenic ametropia such as anisometropia, astigmatism, myopia or hyperopia was 94%, while the specificity was 63%. Following cycloplegia, the sensitivity decreased to 87% and the specificity increased to 80%.

CONCLUSION

Wave-front analyzing refractometry is highly applicable for infant screening. At the present state of development, the efficacy in detecting amblyogenic ametropia is similar to that of other screening techniques and instruments that operate from distance. Cycloplegia enhances the sensitivity in detecting hyperopia and decreases the sensitivity in detecting astigmatism.

Evaluating photoscreeners II: MTI and fortune videorefractor

BACKGROUND

Amblyopia is a public health problem, usually amenable to treatment if detected early. Photoscreeners are camera-based instruments which can detect risk factors for amblyopia such as squint, refractive errors and media opacities.

OBJECTIVE

To evaluate two commercially available photoscreeners, namely the MTI photoscreener (Medical Technology, Iowa City, IA, USA) and the Fortune Optical VRB-100 (Fortune Optical, Padova, Italy) videophotorefractor, in a selected childhood population, having a high prevalence of amblyopia, before undertaking a full-scale trial in the general population.

SUBJECTS AND METHODS

The study design was a double-masked study. One-hundred and five children aged between 12 and 44 months with either normal vision or known visual disorders were photoscreened without cycloplegia using the Fortune and the MTI photoscreeners. Each child had a full ophthalmic examination either on the day of screening or in the preceding 6 months. Risk factors were: any manifest strabismus (squint), hypermetropia >3.5 D, anisometropia > or =1 D sphere, myopia > or =2 D sphere, astigmatism > or =2 D, media opacity or fundus abnormality affecting vision. The prevalence of risk factors for amblyopia was 60%. Photoscreen images were reviewed by two independent masked observers for indicators of amblyopiogenic risk factors and compared to the full ophthalmological examination to determine sensitivity and specificity for each instrument.

RESULTS

Sensitivities and specificities for the detection of risk factors for amblyopia were as follows. Fortune photoscreener: reader 1, sensitivity 60%, specificity 75%; reader 2, sensitivity 68% specificity 86%. MTI photoscreener: reader 1, sensitivity 56%, specificity 79%; reader 2, sensitivity 61%, sensitivity 86%. The results for reader 1 and 2 showed no significant differences for either instrument.

CONCLUSION

Both instruments performed unsatisfactorily in a study population aged 1-4 years with a high prevalence of amblyopiogenic risk factors. Accordingly, we do not believe that either instrument can be recommended to screen for eye disorders in children between the ages of 1 and 4 years because the low prevalence of amblyopia in this population demands very high sensitivity and specificity in order to avoid inappropriate over- or under-referral.

Photoscreening for refractive errors in children and young adults with severe learning disabilities using the MTI photoscreener

PURPOSE

To test the potential ability of the MTI photoscreener to facilitate screening for significant refractive errors in children and young adults with severe learning disabilities.

METHODS

Thirty-eight patients with severe learning disabilities from a special school were examined with the photoscreener, and underwent cycloplegic refraction, an ophthalmological and an orthoptic examination. The age at examination, the cause of learning disability, the pupil size, the number of photographs required for accurate interpretation, the co-operation of the subject and the presence or absence of strabismus were recorded. An educational psychologist had performed a psychological assessment on all the children. The results of the cycloplegic retinoscopy were compared with the photorefraction results.

RESULTS

A photorefraction was possible in 37 patients and cycloplegic refraction in all the patients. The patients had severe learning difficulties with an intelligence quotient of less than 50. All the patients had behavioural problems, 9 patients had associated cerebral palsy, 8 had chronic epilepsy, 1 patient was brain damaged from a non-accidental injury and 1 from a road traffic accident. The mean age of the patients was 10.0 +/- 4.9 years (range 3-18 years), the average pupil diameter during photoscreening was 6.1 +/- 0.9 mm (range 4-8 mm) and the average number of photographs required for each subject was 2.1 +/- 0.9 (range 1-4). The photoscreener detected 10 patients with a manifest strabismus. There was one false positive and one false negative result giving a sensitivity of 92.8% and a specificity of 90%.

CONCLUSION

The examination of children with severe learning disabilities for refractive errors can be extremely difficult. The MTI photoscreener is an effective means of screening such children and young adults for refractive errors and strabismus so that the children with these abnormalities may be targeted for a more detailed evaluation.