Cone dystrophies with negative photopic electroretinogram.

Abstract

A scotopic electroretinogram with an a-wave amplitude larger than the b-wave amplitude traditionally is termed 'negative'. Six male patients with negative photopic electroretinograms were examined; three of them suffered from progressive cone dystrophy, in which negative electroretinograms are unusual. Another patient without symptoms was the brother of a patient with cone dystrophy. These patients are compared with others who characteristically have negative electroretinograms -one patient with incomplete congenital stationary night blindness and another with X linked congenital retinoschisis. Differential diagnosis between these unusual cases of cone dystrophies and X linked retinoschisis or congenital stationary night blindness was possible with funduscopy, adaptometry, and evaluation of progression, but not with the electroretinogram. Inner retinal defects may occur in cone dystrophies as indicated by the negative electroretinogram. The waveform variations between our patients may be due to different inner retinal defects. The findings in two brothers indicate that cone dystrophy and inner retinal defects may be inherited separately. (BrJ Ophthalmol 1993; 77: 404-409) Cone dystrophies are a group of diseases involving the function of retinal cones in various ways. I2 Several different primary defects within the retina seem to exist: degenerations can be separated according to the retinal area and cone types affected. Different involvement of central and peripheral cones has been described.34 Recently selective cone dystrophies affecting only one or two cone types have been separated from generalised cone dystrophies.5'7 In inherited retinal degenerations, however, the location of the primary retinal defect has always been attributed to the photoreceptor-retinal pigment epithelium complex.2 Occasionally electroretinographic findings were described, that indicated a dysfunction of inner retinal layers in cone dystrophies,8'-yet, these findings were ignored. In those cases the bwave was severely reduced compared with a normal or moderately reduced a-wave, resulting in a 'negative' photopic electroretinogram." Similar electroretinograms were seen in incomplete congenital stationary night blindness,'2-" and X linked congenital retinoschisis.'718We analysed retrospectively the records of three patients who suffered from cone dystrophies, had a negative photopic electroretinogram, and in whom X linked retinoschisis and congenital stationary night blindness could be excluded. The patients are compared with patients with incomplete congenital stationary night blindness and X linked retinoschisis. Electrophysiological methodsThe electro-oculographic technique was as described by Rhode et al." The normal range of the light peak/baseline ratio was 187 (SD 36)% (±2 SD); therefore the lower limit of the normal range was 151%.The electroretinographic recording method has been described in detail.'820 The recording protocol includes all stimuli specified by the Figure 1

Dysfunction of transmission in the inner retina: incidence and clinical causes of negative electroretinogram

“…vigabatrin, quinine) [1] or intraocular metallic foreign bodies resulting in ocular siderosis [22]. In addition, negative ERGs were also reported in few cases of retinitis pigmentosa [3] and cone (-rod) dystrophy [5,13] and in further rare disorders (for a detailed list of disorders with negative ERGs and their references, see Koh et al 2001) [15]. Koh and colleagues reported an incidence of 4.8% of negative ERG in their study from one large tertiary care center [15].…”

Inner Retinal Function in Hereditary Retinal Dystrophies

“…A negative ERG has been described in stationary and progressive hereditary retinal disorders as well as acquired retinal dysfunctions. Hereditary disorders were congenital stationary night blindness [Miyake et al, 1986[Miyake et al, , 1987 and the following progressive disorders: x-linked retinoschisis [Peachey et al, 1987], subtypes of cone dystrophies [Kellner and Foerster, 1993], RP [Cideciyan and Jacobson, 1993] and macular dystrophy [Miyake et al, 1989;Kato and Watanabe, 1990], Duchenne muscular dystrophy [Pillers et al, 1993], and Müller cell sheen dystrophy [Gass, 1997;Kellner et al, 1998]. An acquired retinal dysfunction with negative ERG is melanoma-associated retinopathy [Alexander et al, 1992;Kellner et al, 1994].…”

Electroretinogram in Hereditary Retinal Disorders

“…Kellner and Foerster reported three patients with cone dystrophy who had negative photopic electroretinogram (Kellner & Foerster, 1993). This finding showed that at least in a subset of patients with cone dystrophy, additional inner retinal transmission defect may be present.…”

“…However, recently the term electronegative ERG has been used to describe any ERG in which the b-wave amplitude is smaller than the a-wave amplitude whether a-wave amplitude is normal or reduced (Weleber & Francis, 2006). Although the term was initially applied only to the dark-adapted mixed rod-cone ERG, the term has recently been used to describe a similar configuration for the cone ERG (Weleber & Francis, 2006;Kellner & Foerster, 1993;Swain et al, 1997).…”

“…Enhanced S cone sensitivity syndrome: long-term follow-up, electrophysiological and psychophysical findings. Clinical Vision Sciences, Vol 8, Number 5, Kellner et al, 1993, permission conveyed through Copyright Clearance Center, Inc).…”