Sains Malaysiana 48(10)(2019): 2185–2190

http://dx.doi.org/10.17576/jsm-2019-4810-14

Binocular and Monocular Resolution Thresholds throughout Adulthood for Luminance-Modulated and Contrast-Modulated Noise Letters

(Nilai Ambang Resolusi Monokular dan Binokular sepanjang Usia Dewasa untuk Stimulus Hingar Termodulasi Luminans dan Kontras)

PUI JUAN WOI, SHARANJEET-KAUR & MOHD IZZUDDIN HAIROL*

Optometry & Vision Science Programme, Centre for Community Health, Faculty of Health Sciences, Universiti Kebangsaan Malaysia, Jalan Raja Muda Abdul Aziz, 50300 Kuala Lumpur, Federal Territory, Malaysia

Received: 7 October 2018/Accepted: 20 September 2019

ABSTRACT

Contrast-modulated (CM) noise stimuli are thought to be processed in higher, more binocular visual areas compared to luminance-modulated (LM) stimuli, and the ability to perceive them may be more susceptible to ageing. The aim of this study was to determine monocular and binocular resolution thresholds for LM and CM noise letters throughout adulthood. Resolution thresholds for LM and CM noise letters were measured in 25 participants (age 21-70 years old) under monocular and binocular viewing. Stimuli were H, O, T and V letters created by adding or multiplying a luminance modulation function to a binary white noise carrier to create LM and CM noise letters, respectively. Resolution thresholds, determined using a 2-down-1-up staircase procedure, were lower for LM, than for CM, stimuli in both monocular and binocular viewing conditions (p<0.05). Binocular summation ratio for CM noise letters was significantly higher than that for LM noise letters (p<0.05) but declined rapidly with increasing age. For the youngest age group (20-29 years old), binocular resolution threshold was 39% better (~1.5-line improvement on the clinical letter chart) than monocular resolution threshold for CM noise letters, but only 15% better (~0.5-line improvement) when measured with LM noise letters. Binocular performance for CM noise letters declines at a faster rate with increasing age compared to that for LM noise letters. Visual function measurement with contrast-modulated stimuli might be useful to detect subtle binocular vision anomalies that may occur in early adulthood, which may be missed if measured with luminance-based stimuli alone.

Keywords: Ageing; binocular resolution; contrast-modulated; luminance-modulated; monocular resolution

ABSTRAK

Rangsangan hingar modulasi kontras (CM) dianggap diproses lebih tinggi, di kawasan yang mempunyai lebih visual binokular berbanding rangsangan modulasi luminans (LM) dan keupayaan untuk mengamatinya mungkin lebih terdedah kepada penuaan. Matlamat kajian ini adalah untuk menentukan ambang resolusi monokular dan binokular untuk huruf hingar LM dan CM sepanjang tempoh dewasa. Ambang resolusi untuk huruf hingar LM dan CM telah diukur pada 25 peserta (umur 21-70 tahun) di bawah penglihatan monokular dan binokular. Rangsangan adalah huruf H, O, T dan V yang dicipta dengan menambah atau mendarabkan fungsi modulasi luminans kepada pembawa bunyi putih untuk mewujudkan huruf hingar LM dan CM. Ambang resolusi ditentukan menggunakan prosedur tangga 2-turun-1-naik, lebih rendah untuk LM berbanding CM untuk rangsangan dalam kedua-dua keadaan pandangan monokular dan binokular (p < 0.05). Nisbah penjumlahan binokular untuk huruf hingar CM adalah jauh lebih tinggi daripada untuk huruf hingar LM (p < 0.05) tetapi menurun dengan cepat dengan peningkatan umur. Bagi kumpulan umur bongsu (20-29 tahun), ambang resolusi binokular adalah 39% lebih baik (peningkatan garisan ~1.5 dalam carta huruf klinikal) berbanding ambang resolusi monokular untuk huruf hingar CM, tetapi hanya 15% lebih baik (peningkatan garisan ~0.5) apabila diukur dengan huruf hingar LM. Prestasi binokular untuk huruf hingar CM menurun pada kadar yang lebih cepat dengan peningkatan umur berbanding dengan huruf hingar LM. Pengukuran fungsi visual dengan rangsangan modulasi kontras mungkin berguna untuk mengesan anomali visual binokular halus yang mungkin berlaku pada peringkat awal dewasa, yang mungkin terlepas pandang jika diukur dengan berasaskan luminans sahaja.

Kata kunci: Modulasi kontras; modulasi luminans; penuaan; resolusi binokular; resolusi monokular

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*Corresponding author; email: izzuddin.hairol@ukm.edu.my