Electronegative Electroretinograms in the United Arab Emirates

PURPOSE

An electronegative electroretinogram (ERG), defined as having a b:a wave ratio ≤1 in the scotopic flash ERG response, indicates relative inner retinal dysfunction. Causes vary depending upon the study population. In the Arabian Gulf, where inherited retinal disease is relatively prevalent, common diagnoses associated with electronegative ERGs have not been described. In this study, we report the frequency and causes of electronegative ERGs in a cohort of Emirati patients with inherited retinal disease.

METHODS

A retrospective review was performed of all full-field ERGs done for Emirati patients in the Ocular Genetics Service of Cleveland Clinic Abu Dhabi from January 2017 to December 2019. Those who had an electronegative ERG in at least one eye were included in the study.

RESULTS

Out of 137 patients, 9 probands (6.6%) had an electronegative ERG. The mean age at presentation was 24 years (range 5-48 years), and five patients (55.6%) were male. The final clinical diagnoses were congenital stationary night blindness (CSNB) (two TRPM1-related and one Oguchi disease), X-linked retinoschisis (XLRS) (one genetically confirmed and two not genetically tested), cone-rod dystrophy (one CRX-related and one not genetically tested), and enhanced S-cone syndrome (ESCS) (one NRL-related). The one patient who did not have bilateral electronegative ERGs was a male with XLRS whose fellow eye had an unrecordable ERG.

CONCLUSIONS

In this series of Emirati patients, an electronegative ERG was most commonly associated with the inherited retinal diseases recessive CSNB and XLRS. An electronegative ERG was noted in a case of NRL-related ESCS.

Nystagmus in patients with congenital stationary night blindness (CSNB) originates from synchronously firing retinal ganglion cells

Congenital nystagmus, involuntary oscillating small eye movements, is commonly thought to originate from aberrant interactions between brainstem nuclei and foveal cortical pathways. Here, we investigated whether nystagmus associated with congenital stationary night blindness (CSNB) results from primary deficits in the retina. We found that CSNB patients as well as an animal model (nob mice), both of which lacked functional nyctalopin protein (NYX, nyx) in ON bipolar cells (BCs) at their synapse with photoreceptors, showed oscillating eye movements at a frequency of 4-7 Hz. nob ON direction-selective ganglion cells (DSGCs), which detect global motion and project to the accessory optic system (AOS), oscillated with the same frequency as their eyes. In the dark, individual ganglion cells (GCs) oscillated asynchronously, but their oscillations became synchronized by light stimulation. Likewise, both patient and nob mice oscillating eye movements were only present in the light when contrast was present. Retinal pharmacological and genetic manipulations that blocked nob GC oscillations also eliminated their oscillating eye movements, and retinal pharmacological manipulations that reduced the oscillation frequency of nob GCs also reduced the oscillation frequency of their eye movements. We conclude that, in nob mice, synchronized oscillations of retinal GCs, most likely the ON-DCGCs, cause nystagmus with properties similar to those associated with CSNB in humans. These results show that the nob mouse is the first animal model for a form of congenital nystagmus, paving the way for development of therapeutic strategies.

Comparing habitual and i. Scription refractions

BACKGROUND

Many patients voice concerns regarding poor night vision, even when they see 20/20 or better in the exam room. During mesopic and scotopic conditions the pupil size increases, increasing the effects on visual performance of uncorrected (residual) refractive errors. The i.Scription refraction method claims to optimize traditional refractions for mesopic and scotopic conditions, by using the information that the Zeiss i.Profilerplus gathers of ocular aberrations (low and high order). The aim of this study was to investigate any differences between habitual and i.Scription refractions and their relationship to night vision complaints.

METHODS

Habitual, subjective, and i.Scription refractions were obtained from both eyes of eighteen subjects. Low and high order aberrations of the subjects were recorded with the Zeiss i.Profilerplus. The root mean square (RMS) metric was calculated for small (3 mm) and maximum pupil sizes. Subjects rated their difficulty with driving at night on a scale of 1-10.

RESULTS

There was a statistically significant difference between the habitual and i.Scription refractions on both the sphere and cylinder values [(t = 3.12, p < 0.01), (t = 5.39, p < 0.01)]. The same was found when comparing the subjective and i.Scription refractions [(t = 2.31, p = 0.03), (t = 2.54, p = 0.02)]. There were no significant differences found when comparing the sphere and cylinder values between the habitual and subjective refractions or on any combination of spherical equivalent refraction. The maximum pupil size of the subject population on this study, measured with the i.Profilerplus, was 4.8 ± 1.04 mm. Ten out of the eighteen subjects had discomfort at night with an average magnitude of 4 ± 2.7. Ratings of difficulty with night vision correlated with the change in spherical equivalent correction between the habitual and i.Scription refractions (p = 0.01). A sub-analysis of myopic subjects (n = 15) showed an increase in the significance of this relationship (p = 0.002).

CONCLUSIONS

The i.Scription method improves night vision by correcting the sphere and cylinder more precisely. There was a correlation between the amount of change in the cylinder value between habitual and i.Scription prescriptions and the magnitude of the reported visual discomfort at night.

Night Vision after Excimer Laser Photorefractive Keratectomy: Haze and Halos

A series of 85 patients with myopia, up to −6.00D, was treated by photorefractive keratectomy (PRK), using a 5 mm diameter ablation zone. At six months, 38 patients (45%) reported slight disturbances of night vision, nine (11%) of whom had significant problems. Perturbations of night vision after PRK are seen as starbursts and halos around lights. Corneal haze produces the starbursts, which are usually transient. In contrast, halos are myopic blur circles and may be persistent. Using a computer program, halos after PRK were found to be significantly larger than those in emmetropes and myopes corrected with spectacles (p < 0.01). The halos were diminished by using either artificial pupils or negative lens over-correction. In patients with identical bilateral PRK corrections, except for the ablation zone size, the magnitude of the halo was less with 5 mm than 4 mm zones (p < 0.01). Patients treated with 5 mm reported fewer problems attributable to halo than with the 4 mm ablation diameters (p < 0.01). Halos and pupil diameters were measured in nine patients with significant impairment of night vision haze. Those with starbursts had small hyperopic shifts, minimal halos and high haze and light scatter measurements, whilst patients with halos had large hyperopic shifts, little haze and large pupil diameters. Patients with persistent halo problems benefited from either negative lens over-correction or miotics at night.

Mizuo-Nakamura Phenomena

A 21-year-old male presented with a chief complaint of night blindness since early childhood. The patient had no history of hemeralopia or photophobia, and no family history of such illness or use of glasses. On examination, his visual acuity was 6/6 in both eyes. Pupils were reacting normally. Dilated fundus examination revealed diffuse golden-yellow sheen throughout the fundus with prominent retinal vasculature, but arteries and veins were less distinguishable. Choroidal vessels were not visible. The patient was then patched and dark adapted for 6 hours. The dark-adapted fundus showed the disappearance of the golden sheen with normal visible choroidal and retinal vasculature. This characteristic phenomenon observed on fundus examination from dark-adapted state to light adaptation is known as Mizuo-Nakamura phenomenon. Although this phenomenon is classical of Oguchi disease, it is also seen in X-linked cone dystrophy and X-linked retinoschisis. [Ophthalmic Surg Lasers Imaging Retina. 2016;47:1068.].

Treatment of vitamin A deficiency retinopathy with sublingual vitamin A palmitate

PURPOSE

To report treatment of vitamin A deficiency retinopathy with sublingual vitamin A drops.

METHODS

Case report with review of the literature.

RESULTS

A 69-year-old Caucasian woman with a history of small bowel resection presented with progressive symptoms of bilateral nyctalopia and decreased visual acuity. Ophthalmic examination revealed bilateral conjunctival xerosis and fine white granular deposits in the midperipheral retina suggestive of vitamin A deficiency. Full-field electroretinogram (ERG), multifocal ERG (mfERG), and two-color dark adaptometry revealed significant impairment of rod and cone photoreceptor function. Kinetic perimetry demonstrated depressed macular sensitivity with constriction of the finer isopters. After 5 months of treatment with sublingual vitamin A drops, the patient's vision, ERG, mfERG, dark adaptometry, and perimetry normalized. A review of the literature summarizing the electrophysiologic testing in vitamin A deficiency is also discussed.

CONCLUSIONS

This case highlights novel observations on the effects of sublingual vitamin A supplementation for acquired vitamin A deficiency retinopathy. Sublingual vitamin A may represent a viable and efficacious treatment modality for vitamin A deficiency.

The Physiology, Pathology, and Pharmacology of Voltage-Gated Calcium Channels and Their Future Therapeutic Potential

Voltage-gated calcium channels are required for many key functions in the body. In this review, the different subtypes of voltage-gated calcium channels are described and their physiologic roles and pharmacology are outlined. We describe the current uses of drugs interacting with the different calcium channel subtypes and subunits, as well as specific areas in which there is strong potential for future drug development. Current therapeutic agents include drugs targeting L-type Ca(V)1.2 calcium channels, particularly 1,4-dihydropyridines, which are widely used in the treatment of hypertension. T-type (Ca(V)3) channels are a target of ethosuximide, widely used in absence epilepsy. The auxiliary subunit α2δ-1 is the therapeutic target of the gabapentinoid drugs, which are of value in certain epilepsies and chronic neuropathic pain. The limited use of intrathecal ziconotide, a peptide blocker of N-type (Ca(V)2.2) calcium channels, as a treatment of intractable pain, gives an indication that these channels represent excellent drug targets for various pain conditions. We describe how selectivity for different subtypes of calcium channels (e.g., Ca(V)1.2 and Ca(V)1.3 L-type channels) may be achieved in the future by exploiting differences between channel isoforms in terms of sequence and biophysical properties, variation in splicing in different target tissues, and differences in the properties of the target tissues themselves in terms of membrane potential or firing frequency. Thus, use-dependent blockers of the different isoforms could selectively block calcium channels in particular pathologies, such as nociceptive neurons in pain states or in epileptic brain circuits. Of important future potential are selective Ca(V)1.3 blockers for neuropsychiatric diseases, neuroprotection in Parkinson's disease, and resistant hypertension. In addition, selective or nonselective T-type channel blockers are considered potential therapeutic targets in epilepsy, pain, obesity, sleep, and anxiety. Use-dependent N-type calcium channel blockers are likely to be of therapeutic use in chronic pain conditions. Thus, more selective calcium channel blockers hold promise for therapeutic intervention.

Empirical mode decomposition and neural network for the classification of electroretinographic data

The processing of biosignals is increasingly being utilized in ambulatory situations in order to extract significant signals' features that can help in clinical diagnosis. However, this task is hampered by the fact that biomedical signals exhibit a complex behavior characterized by strong nonlinear and non-stationary properties that cannot always be perceived by simple visual examination. New processing methods need be considered. In this context, we propose a signal processing method, based on empirical mode decomposition and artificial neural networks, to analyze electroretinograms, i.e., the retinal response to a light flash, with the aim to detect and classify retinal diseases. The present application focuses on two retinal pathologies: achromatopsia, which is a cone disease, and congenital stationary night blindness, which affects the photoreceptoral signal transmission. The results indicate that, under suitable conditions, the method proposed here has the potential to provide a powerful tool for routine clinical examinations, since it is able to recognize with high level of confidence the eventual presence of one of the two pathologies.

Lrit3 deficient mouse (nob6): a novel model of complete congenital stationary night blindness (cCSNB)

Mutations in LRIT3, coding for a Leucine-Rich Repeat, immunoglobulin-like and transmembrane domains 3 protein lead to autosomal recessive complete congenital stationary night blindness (cCSNB). The role of the corresponding protein in the ON-bipolar cell signaling cascade remains to be elucidated. Here we genetically and functionally characterize a commercially available Lrit3 knock-out mouse, a model to study the function and the pathogenic mechanism of LRIT3. We confirm that the insertion of a Bgeo/Puro cassette in the knock-out allele introduces a premature stop codon, which presumably codes for a non-functional protein. The mouse line does not harbor other mutations present in common laboratory mouse strains or in other known cCSNB genes. Lrit3 mutant mice exhibit a so-called no b-wave (nob) phenotype with lacking or severely reduced b-wave amplitudes in the scotopic and photopic electroretinogram (ERG), respectively. Optomotor tests reveal strongly decreased optomotor responses in scotopic conditions. No obvious fundus auto-fluorescence or histological retinal structure abnormalities are observed. However, spectral domain optical coherence tomography (SD-OCT) reveals thinned inner nuclear layer and part of the retina containing inner plexiform layer, ganglion cell layer and nerve fiber layer in these mice. To our knowledge, this is the first time that SD-OCT technology is used to characterize an animal model for CSNB. This phenotype is noted at 6 weeks and at 6 months. The stationary nob phenotype of mice lacking Lrit3, which we named nob6, confirms the findings previously reported in patients carrying LRIT3 mutations and is similar to other cCSNB mouse models. This novel mouse model will be useful for investigating the pathogenic mechanism(s) associated with LRIT3 mutations and clarifying the role of LRIT3 in the ON-bipolar cell signaling cascade.

Cav1.4 IT mouse as model for vision impairment in human congenital stationary night blindness type 2

Mutations in the CACNA1F gene encoding the Cav1.4 Ca (2+) channel are associated with X-linked congenital stationary night blindness type 2 (CSNB2). Despite the increasing knowledge about the functional behavior of mutated channels in heterologous systems, the pathophysiological mechanisms that result in vision impairment remain to be elucidated. This work provides a thorough functional characterization of the novel IT mouse line that harbors the gain-of-function mutation I745T reported in a New Zealand CSNB2 family. (1) Electroretinographic recordings in IT mice permitted a direct comparison with human data. Our data supported the hypothesis that a hyperpolarizing shift in the voltage-dependence of channel activation-as seen in the IT gain-of-function mutant (2)-may reduce the dynamic range of photoreceptor activity. Morphologically, the retinal outer nuclear layer in adult IT mutants was reduced in size and cone outer segments appeared shorter. The organization of the outer plexiform layer was disrupted, and synaptic structures of photoreceptors had a variable, partly immature, appearance. The associated visual deficiency was substantiated in behavioral paradigms. The IT mouse line serves as a specific model for the functional phenotype of human CSNB2 patients with gain-of-function mutations and may help to further understand the dysfunction in CSNB.

Assessment of night vision problems in patients with congenital stationary night blindness

Congenital Stationary Night Blindness (CSNB) is a retinal disorder caused by a signal transmission defect between photoreceptors and bipolar cells. CSNB can be subdivided in CSNB2 (rod signal transmission reduced) and CSNB1 (rod signal transmission absent). The present study is the first in which night vision problems are assessed in CSNB patients in a systematic way, with the purpose of improving rehabilitation for these patients. We assessed the night vision problems of 13 CSNB2 patients and 9 CSNB1 patients by means of a questionnaire on low luminance situations. We furthermore investigated their dark adapted visual functions by the Goldmann Weekers dark adaptation curve, a dark adapted static visual field, and a two-dimensional version of the “Light Lab”. In the latter test, a digital image of a living room with objects was projected on a screen. While increasing the luminance of the image, we asked the patients to report on detection and recognition of objects. The questionnaire showed that the CSNB2 patients hardly experienced any night vision problems, while all CSNB1 patients experienced some problems although they generally did not describe them as severe. The three scotopic tests showed minimally to moderately decreased dark adapted visual functions in the CSNB2 patients, with differences between patients. In contrast, the dark adapted visual functions of the CSNB1 patients were more severely affected, but showed almost no differences between patients. The results from the “2D Light Lab” showed that all CSNB1 patients were blind at low intensities (equal to starlight), but quickly regained vision at higher intensities (full moonlight). Just above their dark adapted thresholds both CSNB1 and CSNB2 patients had normal visual fields. From the results we conclude that night vision problems in CSNB, in contrast to what the name suggests, are not conspicuous and generally not disabling.

Night myopia studied with an adaptive optics visual analyzer

PURPOSE

Eyes with distant objects in focus in daylight are thought to become myopic in dim light. This phenomenon, often called "night myopia" has been studied extensively for several decades. However, despite its general acceptance, its magnitude and causes are still controversial. A series of experiments were performed to understand night myopia in greater detail.

METHODS

We used an adaptive optics instrument operating in invisible infrared light to elucidate the actual magnitude of night myopia and its main causes. The experimental setup allowed the manipulation of the eye's aberrations (and particularly spherical aberration) as well as the use of monochromatic and polychromatic stimuli. Eight subjects with normal vision monocularly determined their best focus position subjectively for a Maltese cross stimulus at different levels of luminance, from the baseline condition of 20 cd/m(2) to the lowest luminance of 22 × 10(-6) cd/m(2). While subjects performed the focusing tasks, their eye's defocus and aberrations were continuously measured with the 1050-nm Hartmann-Shack sensor incorporated in the adaptive optics instrument. The experiment was repeated for a variety of controlled conditions incorporating specific aberrations of the eye and chromatic content of the stimuli.

RESULTS

We found large inter-subject variability and an average of -0.8 D myopic shift for low light conditions. The main cause responsible for night myopia was the accommodation shift occurring at low light levels. Other factors, traditionally suggested to explain night myopia, such as chromatic and spherical aberrations, have a much smaller effect in this mechanism.

CONCLUSIONS

An adaptive optics visual analyzer was applied to study the phenomenon of night myopia. We found that the defocus shift occurring in dim light is mainly due to accommodation errors.

A phenotypic study of congenital stationary night blindness (CSNB) associated with mutations in the GRM6 gene

PURPOSE

To describe the clinical phenotype and the molecular pathology in a group of patients with congenital stationary night blindness due to mutations in GRM6, a gene encoding the ON bipolar metabotropic glutamate receptor 6 (mGluR6).

METHODS

Nine patients from seven families (age range, 7-75; median, 10 years) with a clinical diagnosis of autosomal recessive complete congenital stationary night blindness were ascertained. Clinical examination, imaging and electrophysiological assessment were performed. The coding region and intron-exon boundaries of GRM6 were sequenced.

RESULTS

The median visual acuity for the cohort was 0.2 logMAR (range 0-3). Most patients had myopic astigmatism with the median spherical equivalent being -5.375 dioptres (-0.125 to -18.75). Fundoscopy was within normal limits in 15 eyes; there was severe myopic maculopathy in three eyes. Other secondary complications included face turn because of nystagmus and strabismic amblyopia. All patients had electronegative dark-adapted bright white flash electroretinograms (ERGs) consistent with dysfunction occurring postphototransduction. In the two oldest subjects (aged 75 and 58 years), there was additional photoreceptor dysfunction in keeping with myopic degeneration. ON-OFF ERGs showed generalized cone ON bipolar system dysfunction in all five patients tested. Pattern ERG P50 was normal (Ν = 1), subnormal (N = 2) or undetectable (N = 2). Nine mutations in GRM6 were detected in all seven families; six of these changes were novel.

CONCLUSIONS

The phenotype associated with GRM6 mutation is variable in terms of presentation, refractive error, visual acuity and macular function. ERGs are electronegative and suggest ON-pathway dysfunction.

[A case of Oguchi disease with disappearance of golden tapetal-like fundus reflex after vitreous resection]

BACKGROUND

Oguchi disease is a form of congenital stationary night-blindness characterized by a golden tapetal fundus reflex. This reflex is known to disappear in the dark-adapted state ("Mizuo-Nakamura phenomenon"). The origin of the reflex is not clear. We report a case of Oguchi disease with the disappearance of the golden tapetal reflex after vitreous resection.

CASE

An 80-year-old man was referred for rhegmatogenous retinal detachment of the left eye. Golden tapetal reflex was observed in both eyes. Negative b-wave in the electroretinogram and mutation in the SAG gene indicated Oguchi disease. Pars plana vitrectomy and posterior hyaloid membrane peeling were performed. The tapetal reflex in the all regions of the fundus in the operated eye disappeared after the retina was reattached. The reflex partially recovered 2 years after the operation.

CONCLUSION

It is suggested that the change in vitreo-retinal interface after a vitreous operation leads to the disappearance of the reflex. This report presents a hypothesis on the origin of the golden tapetal reflex in Oguchi disease.

Longitudinal assessment of retinal structure and function reveals a rod-cone degeneration in a guinea pig model initially presented as night blind

We have previously reported a naturally occurring retinopathy in a population of guinea pigs, where the affected animals presented a defect of the rod-mediated vision. The purpose of this study was to investigate if the mutants were affected with a stationary or degenerative retinopathy and to identify the cellular origin of this unique disorder. Electroretinogram (ERG) [postnatal day 1 (P1) to P450], light (LM) and electron microscopy (EM) [P5, P150, P450], and immunohistochemistry [P30, P150, P450] were evaluated from normal and mutant animals. Irrespective of age, the scotopic ERGs of mutants could only be evoked by bright flashes, and the resulting ERGs were of photopic waveform. Interestingly, the amplitude of the cone and the rod/cone a-waves was always of smaller amplitude in mutants, but this difference tended to decrease with age. In contrast, the b-waves were of larger amplitude than normal in photopic ERGs obtained prior to age 25 (days) and prior to age 10 for rod/cone ERGs. LM revealed, in mutants, an absence of the outer segment layer (OSL) with a reduction in the outer nuclear layer (ONL) thickness. EM disclosed the presence of cone outer segment (OS) while no rod OS could be evidenced. Immunohistochemistry revealed the presence of rhodopsin, both cone opsins as well as normal synaptophysin immunoreactivity. Finally, neither the retinal structure nor the function in the mutants achieved normal development. Results suggest that mutant animals are suffering from a degenerative retinal disorder that affects the structure and function of rods and cones.

Mutations in TRPM1 are a common cause of complete congenital stationary night blindness

Congenital stationary night blindness (CSNB) is a clinically and genetically heterogeneous group of retinal disorders characterized by nonprogressive impaired night vision and variable decreased visual acuity. We report here that six out of eight female probands with autosomal-recessive complete CSNB (cCSNB) had mutations in TRPM1, a retinal transient receptor potential (TRP) cation channel gene. These data suggest that TRMP1 mutations are a major cause of autosomal-recessive CSNB in individuals of European ancestry. We localized TRPM1 in human retina to the ON bipolar cell dendrites in the outer plexifom layer. Our results suggest that in humans, TRPM1 is the channel gated by the mGluR6 (GRM6) signaling cascade, which results in the light-evoked response of ON bipolar cells. Finally, we showed that detailed electroretinography is an effective way to discriminate among patients with mutations in either TRPM1 or GRM6, another autosomal-recessive cCSNB disease gene. These results add to the growing importance of the diverse group of TRP channels in human disease and also provide new insights into retinal circuitry.

[Long-term observation of two cases of enhanced S-cone syndrome]

BACKGROUND

We report two cases of enhanced S-cone syndrome (ESCS), one in a patient observed for 20 years since age 31 and the other in an elderly patient with ESCS who underwent cataract surgery.

CASE REPORT

Case 1. A 31-year-old man complained of night blindness and decreased vision. At the initial visit, his corrected visual acuity was 0.7 OD and 0.3 OS. Funduscopy revealed retinal degeneration near the vascular arcade and cystic change in the macular area in both eyes. It was diagnosed as ESCS by electroretinogram (ERG) findings. During a 20-year observation, the cystic change in the macular area became ambiguous and pigmentation appeared in the retinal degeneration region, Goldmann perimetry showed remarkable constriction of I /4 isopter, and ERG showed reduction of amplitude. At age 50, his corrected visual acuity was 0.4 OD and 0.4 OS. Case 2. A 78-year-old woman complained of night blindness and decreased vision. At the initial visit, her corrected visual acuity was 0.03 OD and 0.07 OS. Advanced nuclear cataract was seen in both eyes, and funduscopy revealed retinal degeneration near the vascular arcade. It was diagnosed as ESCS by ERG findings. Cataract surgery was done in both eyes, and postoperative visual acuity was 0.3 OD and 0.2 OS, and she has maintained the same visual acuity for two years.

CONCLUSIONS

These cases indicate that retinal function of patients with ESCS decreases gradually after middle age, and that even if a cystic change in the macular area becomes ambiguous, vision does not improve. Some retinal function of ESCS patients can be maintained into old age.

Association of lens opacities, intraocular straylight, contrast sensitivity and visual acuity in European drivers

PURPOSE

To study the relationship between lens opacity and intraocular straylight, visual acuity and contrast sensitivity.

METHODS

We investigated 2422 drivers in five clinics in different European Union (EU) member states aged between 20 and 89 years as part of a European study into the prevalence of visual function disorders in drivers. We measured visual acuity [Early Treatment Diabetic Retinopathy Study (ETDRS) chart], contrast sensitivity (Pelli-Robson chart) and intraocular straylight (computerized straylight meter). Lens opacities were graded with the Lens Opacities Classification System III (LOCS) without pupillary dilation. Participants answered the National Eye Institute Visual Functioning Questionnaire - 25.

RESULTS

Intraocular straylight was related more strongly to LOCS score than to both visual acuity and contrast sensitivity. Visual acuity and contrast sensitivity were correlated to each other well, but to intraocular straylight to a much lesser extent. Self-reported visual quality was best related to contrast sensitivity; night driving difficulty was best related to visual acuity.

CONCLUSION

Straylight is found to have added value for visual function assessment in drivers, whereas if visual acuity is known contrast sensitivity has limited added value.

Corneal wavefront-guided retreatments for significant night vision symptoms after myopic laser refractive surgery

PURPOSE

To evaluate the results of corneal wavefront (WF)-guided enhancements in patients with night vision symptoms and significantly high positive spherical aberration (SA) after myopic laser refractive surgery.

DESIGN

Noncomparative, interventional case series.

METHODS

Twenty-eight eyes of 20 patients with significant night vision symptoms and positive corneal SA (Z(4)(0)) higher than 0.5 microm after myopic laser refractive surgery were included in the study at Vissum-Instituto Oftalmologico de Alicante, Spain. Enhancement surgery was planned to remove residual refractive error and corneal SA (Z(4)(0)) in all cases. All patients underwent corneal WF-guided excimer laser retreatments using the ESIRIS/SCHWIND excimer laser system (Schwind Eye Tech Solutions, Kleinostham, Germany). The main outcome measures were visual symptoms, change in corneal SA (Z(4)(0)), and corneal asphericity (Q-value).

RESULTS

Subjective reports of night vision symptoms were improved in all patients. Mean corneal SA (Z(4)(0)) decreased from 0.75 +/- 0.19 microm before surgery to 0.43 +/- 0.42 microm after surgery (P < .001). Mean asphericity in the 4.5-mm zone significantly decreased from 1.02 +/- 1.07 before surgery to 0.52 +/- 0.88 after surgery (P = .008), and the mean asphericity in 8 mm did not change significantly (P = .362). The mean spherical equivalent significantly shifted to hyperopia from -0.22 +/- 1.14 diopters (D) before surgery to 0.33 +/- 0.54 D after surgery (P = .025).

CONCLUSIONS

Cornea wavefront-guided retreatment was effective in improving subjective night vision symptoms, reducing corneal SA, and decreasing asphericity in eyes that underwent myopic laser refractive surgery.

The luminance-response function of the human photopic electroretinogram: a mathematical model

The luminance-response function of the brief flash full-field photopic electroretinogram (ERG) rises to a peak before falling to a sub-maximal plateau -- the 'photopic hill'. The combination of on- and off-responses inherent in the brief flash photopic ERG suggests that this luminance-response function could be modelled by the sum of a Gaussian function and a logistic growth function. Photopic ERGs to a luminance series of brief flashes against three different background luminances recorded from seven healthy adults showed the characteristic 'photopic hill' function for b-wave amplitudes which were satisfactorily fitted with the sum of a Gaussian curve and a logistic growth curve. As background luminance increased, both components shifted to the right on the luminance axis. The Gaussian component increased in amplitude while the logistic growth function component decreased in amplitude. The luminance-response function of a complete congenital stationary night blindness patient had almost no logistic growth component.

Gradient of deficit in cone responses in the incomplete form of congenital stationary night blindness revealed by multifocal electroretinography

Multifocal electroretinograms were recorded in one case of incomplete form of congenital stationary night blindness. First order kernel revealed reduced cone macular P1 responses with normal implicit time (22.7 nV, 33.3 ms; normal 43.3 +/- 8.2 nV, 32.7 +/- 0.6 ms) whereas more peripheral responses exhibited low responses of extremely delayed implicit time (5.1 nV, 47.5 ms; normal 7.4 +/- 2.1 nV, 32.3 +/- 0.8 ms). Responses from the first slice of the second kernel were present in the macular area but absent from the more peripheral areas. In comparison, mfERGs in the complete form of CSNB showed normal amplitude but slightly delayed responses at all eccentricities and normal second kernel responses. Results are discussed in terms of the dichotomy in synaptic transmission between macular and peripheral cones.

Fundus albipunctatus in a 6-year old girl due to compound heterozygous mutations in the RDH5 gene

We report a case study of Fundus Albipunctatus (FA) due to compound heterozygous mutations in RDH5, the gene encoding for the 11-cis-retinal dehydrogenase (RDH). A 6-year old Hispanic American female with a clinical presentation suggestive of FA underwent dark-adapted full-field flash electroretinography (ERG) at 30 and 120 min. The pattern of ERG abnormalities was consistent with the working diagnosis FA. However, only ERG responses to dim stimuli were profoundly affected, and maximal ERG responses were already near normal after only 30 min of dark adaptation. The patient also demonstrated a subnormal maximal ERG response b/a-wave ratio at 30 min that resolved after 120 min of dark adaptation. When measurable, dark-adapted post-receptoral responses were normal in timing under all circumstances, and became increasingly faster after prolonged dark adaptation. Cone-driven responses were completely normal at this young age. Sequencing of the RDH5 gene revealed two distinct missense mutations, a G238W mutation, previously reported in patients with FA, and a D128N mutation, which has not been reported before but is known to cause reduced 11-cis-RDH activity. These findings confirmed the clinical and functional diagnosis of FA and excluded that of retinitis punctata albescens (RPA). The behavior of dark-adapted ERG responses in FA displays characteristics that differ from those of RPA patients, which may be useful to differentiate functionally these two conditions at their common albipunctate stages.

Calcium channelopathies

Intracellular calcium ([Ca2+]i) is highly regulated in eukaryotic cells. The free [Ca2+]i is approximately four orders of magnitude less than that in the extracellular environment. It is, therefore, an electrochemical gradient favoring Ca2+ entry, and transient cellular activation increasing Ca2+ permeability will lead to a transient increase in [Ca2+]i. These transient rises of [Ca2+]i trigger or regulate diverse intracellular events, including metabolic processes, muscle contraction, secretion of hormones and neurotransmitters, cell differentiation, and gene expression. Hence, changes in [Ca2+]i act as a second messenger system coordinating modifications in the external environment with intracellular processes. Notably, information on the molecular genetics of the membrane channels responsible for the influx of Ca2+ ions has led to the discovery that mutations in these proteins are linked to human disease. Ca2+ channel dysfunction is now known to be the basis for several neurological and muscle disorders such as migraine, ataxia, and periodic paralysis. In contrast to other types of genetic diseases, Ca2+ channelopathies can be studied with precision by electrophysiological methods, and in some cases, the results have been highly rewarding with a biophysical phenotype that correlates with the ultimate clinical phenotype. This review outlines recent advances in genetic, molecular, and pathophysiological aspects of human Ca2+ channelopathies.

The dilemma of the late-onset “Dystrophy”

A case of late-onset (age 51) visual loss and night-blindness is presented to illustrate the challenges of diagnosis. This patient had anti-enolase antibodies, and demonstrates the importance of auto-immune retinopathy as a potential cause of late-onset retinal "dystrophy."

Electroretinographic assessment and diagnostic reappraisal of children with visual dysfunction: A prospective study

PURPOSE

To assess the presence or absence of a retinal cause of visual impairment using electroretinography (ERG) in children with no obvious discernable cause on ocular examination.

DESIGN

Prospective observational case series.

MATERIALS AND METHODS

A prospective study was carried out involving 120 children with the mean age 4.4+/-3.2 years with visual dysfunction. All children underwent ERG under general anesthesia using a special handheld mini-Ganzfeld (Kurbisfeld) dome.

RESULTS

Fifty-two (43.3%) children were male and 68 (56.7%) were female. The clinical diagnosis was as follows: Leber's congenital amaurosis (LCA) (n=47), achromatopsia (n=25), congenital stationary night blindness (CSNB) (n=9) and others (unclassifiable, n=39). The visual acuity ranged from perception of light (PL) to PL with projection in children with LCA. In the rest (n=73), some sort of visually guided behavior was discernable. Following ERG, a diagnostic reappraisal resulted as follows: LCA (n=49), achromatopsia (n=28), CSNB (n=4), cone-rod dystrophy (n=22), rod-cone degeneration (n=7), normal (n=8) and others (unclassifiable, n=2). Except for the two unclassifiable cases, ERG was successful in the diagnosis or exclusion of retinal dysfunction in the rest. By Pearson Chi-square test, there was a statistically significant association between the clinical and ERG diagnosis (P < 0.001).

CONCLUSION

LCA was the commonest cause of visual dysfunction in our series. A statistically significant correlation between clinical and electrophysiological diagnosis was seen. ERG helped in firmly establishing the presence or absence of global retinal dysfunction in the majority (118/120) of pediatric patients with visual dysfunction.

Improvement of scotopic electroretinograms and night blindness with recovery of serum zinc levels

BACKGROUND

We sought to determine the cause of reduced scotopic and photopic electroretinograms (ERGs) and night blindness in a 46-year-old man with liver dysfunction but no history of alcoholism.

CASE

A 46-year-old Japanese man with a complaint of visual difficulties in dim light for 1 month.

OBSERVATIONS

By electrophysiological investigation, the patient was found to have low levels of serum zinc and vitamin A on admission. The rod b wave was unrecordable, and the bright-flash ERGs were reduced, with the a wave > b wave. The amplitudes of the cone and 30-Hz flicker responses were also reduced, and their implicit times were prolonged. Three weeks after admission, the patient's serum zinc level recovered to normal levels, but his serum vitamin A level was still low. The symptoms of night blindness were gone, and the rod ERGs and single bright-flash responses were within normal limits. However, the cone ERGs and 30-Hz flicker responses were still depressed.

CONCLUSIONS

The recovery of scotopic function together with the recovery of zinc but not vitamin A levels suggests that the ERG changes were most likely related to low zinc levels.

Electrophysiological findings in persons with nyctalopia

INTRODUCTION

Ophthalmologists are occasionally confronted with an individual presenting with nyctalopia (i.e., a relatively greater difficulty seeing at night). When there is no accompanying abnormality seen in the fundus, visual electrophysiology becomes useful as an objective means of assessing rod (scotopic) photoreceptor function or pathway defects.

MATERIALS AND METHODS

A retrospective study was performed on 50 consecutive patients, aged less than 40 years, with seemingly normal fundi and good vision [visual acuity (VA) >6/12] presenting to the Visual Electrodiagnostic Unit, Singapore National Eye Centre, for the investigation of nyctalopia over a 2-year period. Subjective scotopic threshold sensitivity (STS) and objective full-field electroretinogram (ERG) were performed. Persons with abnormal test results were identified.

RESULTS

Normal ERG scotopic responses were obtained in 74% of subjects. There was no significant difference in age, refraction and STS levels between subjects with abnormal and normal ERG. In the group with abnormal scotopic ERG responses, 9 were identified to have nonspecific rod dysfunction, 2 had rod-cone dystrophies and 2 had ERG changes suggestive of congenital stationary night blindness (CSNB).

CONCLUSION

A large number of subjects presenting with nyctalopia had normal ERG findings. We can only assume that in these patients, no significant rod pathway dysfunction exists and that optical (e.g., night or instrument myopia) and psychological aetiologies should be considered. The fact that an abnormal result occurs in 26%, however, suggests that ncytalopia should be evaluated with electrophysiolgoical testing even when the fundi appear normal.

A novel homozygous GRK1 mutation (P391H) in 2 siblings with Oguchi disease with markedly reduced cone responses

PURPOSE

The only mutations reported to date in Japanese patients with Oguchi disease, a rare form of stationary night blindness with autosomal recessive transmission, have been in the SAG (arrestin) gene. The objective of this study was to describe the ophthalmic features and a novel mutation in the GRK1 (rhodopsin kinase) gene in 2 Japanese patients with Oguchi disease.

DESIGN

Molecular genetic and observational case study.

PARTICIPANTS

A consanguineous family including 2 siblings with Oguchi disease (a 35-year-old man and a 31-year-old woman).

METHODS

Best-corrected visual acuity (BCVA), fundus examinations, Goldmann perimetry, color vision tests, and full-field electroretinograms (ERGs) were evaluated. Mutation screening of the SAG and GRK1 genes was performed with polymerase chain reaction amplification and direct sequencing.

MAIN OUTCOME MEASURES

Mutations in the GRK1 gene, BCVA, color vision, fundus photographs, visual fields, and ERG findings.

RESULTS

Molecular analysis revealed a novel homozygous missense mutation (p.P391H) in the GRK1 gene in both patients. Proline 391 is not only within the functionally important catalytic domain, but is also a phylogenetically conserved amino acid residue among GRK1 orthologs and homologs. No mutation was found in the SAG gene. The unaffected parents were heterozygous carriers of the mutation. Both patients had night blindness, 1.5 BCVA for each eye, normal color vision, and typical fundus appearance with golden-yellow discoloration. The visual fields were normal in the male sibling. The ERGs showed no rod B waves, reduced standard combined responses, and markedly reduced single-flash cone and 30-Hz flicker responses in both patients.

CONCLUSIONS

A novel homozygous GRK1 mutation (p.P391H) was found in 2 Japanese siblings with Oguchi disease. Visual function in the 2 patients has not deteriorated with age, indicating that the disease is stationary. This is the first report of any patient with GRK1-associated Oguchi disease with markedly reduced cone responses.

Mutations in CABP4, the gene encoding the Ca2+-binding protein 4, cause autosomal recessive night blindness

Mutations in genes encoding either components of the phototransduction cascade or proteins presumably involved in signaling from photoreceptors to adjacent second-order neurons have been shown to cause congenital stationary night blindness (CSNB). Sequence alterations in CACNA1F lead to the incomplete type of CSNB (CSNB2), which can be distinguished by standard electroretinography (ERG). CSNB2 is associated with a reduced rod b-wave, a substantially reduced cone a-wave, and a reduced 30-Hz flicker ERG response. CACNA1F encodes the alpha 1-subunit of an L-type Ca2+ channel (Cav1.4 alpha ), which is specific to photoreceptors and is present at high density in the synaptic terminals. Ten of our patients with CSNB2 showed no mutation in CACNA1F. To identify the disease-causing mutations, we used a candidate-gene approach. CABP4, a member of the calcium-binding protein (CABP) family, is located in photoreceptor synaptic terminals and is directly associated with the C-terminal domain of the Cav1.4 alpha . Mice lacking either Cabp4 or Cav1.4 alpha display a CSNB2-like phenotype. Here, we report for the first time that mutations in CABP4 lead to autosomal recessive CSNB. Our studies revealed homozygous and compound heterozygous mutations in two families. We also show that these mutations reduce the transcript levels to 30%-40% of those in controls. This suggests that the reduced amount of CABP4 is the reason for the signaling defect in these patients.

Phototransduction in a transgenic mouse model of Nougaret night blindness

The Nougaret form of dominant stationary night blindness is linked to a G38D mutation in the rod transducin-alpha subunit (Talpha). In this study, we have examined the mechanism of Nougaret night blindness using transgenic mice expressing TalphaG38D. The biochemical, electrophysiological, and vision-dependent behavioral analyses of the mouse model revealed a unique phenotype of reduced rod sensitivity, impaired activation, and slowed recovery of the phototransduction cascade. Two key deficiencies in TalphaG38D function, its poor ability to activate PDE6 (cGMP phosphodiesterase) and decreased GTPase activity, are found to be the major mechanisms altering visual signaling in transgenic mice. Despite these defects, rod-mediated sensitivity in heterozygous mice is not decreased to the extent seen in heterozygous Nougaret patients.

Different amino acid substitutions at the same position in rhodopsin lead to distinct phenotypes

PURPOSE

Identification of a novel rhodopsin mutation in a family with retinitis pigmentosa and comparison of the clinical phenotype to a known mutation at the same amino acid position.

METHODS

Screening for mutations in rhodopsin was performed in 78 patients with retinitis pigmentosa. All exons and flanking intronic regions were amplified by PCR, sequenced, and compared to the reference sequence derived from the National Center for Biotechnology Information (NCBI, Bethesda, MD) database. Patients were characterized clinically according to the results of best corrected visual acuity testing (BCVA), slit lamp examination (SLE), funduscopy, Goldmann perimetry (GP), dark adaptometry (DA), and electroretinography (ERG). Structural analyses of the rhodopsin protein were performed with the Swiss-Pdb Viewer program available on-line (http://www.expasy.org.spdvbv/ provided in the public domain by Swiss Institute of Bioinformatics, Geneva, Switzerland).

RESULTS

A novel rhodopsin mutation (Gly90Val) was identified in a Swiss family of three generations. The pedigree indicated autosomal dominant inheritance. No additional mutation was found in this family in other autosomal dominant genes. The BCVA of affected family members ranged from 20/25 to 20/20. Fundus examination showed fine pigment mottling in patients of the third generation and well-defined bone spicules in patients of the second generation. GP showed concentric constriction. DA demonstrated monophasic cone adaptation only. ERG revealed severely reduced rod and cone signals. The clinical picture is compatible with retinitis pigmentosa. A previously reported amino acid substitution at the same position in rhodopsin leads to a phenotype resembling night blindness in mutation carriers, whereas patients reported in the current study showed the classic retinitis pigmentosa phenotype. The effect of different amino acid substitutions on the three-dimensional structure of rhodopsin was analyzed by homology modeling. Distinct distortions of position 90 (shifts in amino acids 112 and 113) and additional hydrogen bonds were found.

CONCLUSIONS

Different amino acid substitutions at position 90 of rhodopsin can lead to night blindness or retinitis pigmentosa. The data suggest that the property of the substituted amino acid distinguishes between the phenotypes.

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

BACKGROUND

Only limited data exist on the incidence of negative electroretinograms (ERG) in clinical practice. The purpose of this study is therefore to determine the incidence and clinical causes of a negative ERG in a tertiary care centre focused on inherited and acquired retinal degenerations.

METHODS

All ERGs recorded (in accordance with ISCEV standards) in our electrophysiological laboratory from 1992 to 2004 were retrospectively reviewed. The negative ERGs (criterion: ERG with b:a wave ratio<or=1 in the scotopic standard combined response in at least one eye) were analysed in the context of further clinical results. The photopic ON- and OFF-responses were recorded with long duration (200 ms) stimuli.

RESULTS

A total of 1999 ERGs from 1644 patients were performed during the study period. 47/1644 patients (2.9%) presented with a negative ERG and were included in the study. Clinical diagnoses included inherited retinal dystrophies [X-linked congenital retinoschisis (XRS) (n=17), congenital stationary night blindness (CSNB) (n=6), retinitis pigmentosa (RP) (n=6), cone (-rod) dystrophy (n=5), choroideremia (n=1), Müller cell sheen dystrophy (MCSD) (n=1)] and acquired retinopathies (melanoma-associated retinopathy (MAR) (n=1), vigabatrin retinotoxicity (n=1)). In nine patients a definitive diagnosis could not be established. Unilateral negative ERGs were seen in 10/37 patients where ERG was bilaterally recorded. The fellow eye presented with a b:a wave ratio >1 (8 eyes) or ERG responses were not detectable (2 eyes). Photopic ON- and OFF-responses were recorded in 38 eyes of 29 patients and 32/38 eyes presented with a negative ERG. The ON-response was reduced in 25/32 eyes, whereas the OFF-response was reduced in only 11/32 eyes.

CONCLUSIONS

The incidence of a negative ERG can differ between the laboratories depending on the causes for ERG recording and was in our laboratory 2.9% in a consecutive series of patients with inherited or acquired retinal degenerations. A disorder characteristically associated with negative ERG (e.g. XRS, CSNB, MAR) was diagnosed in 53% of these patients, whereas in 47% the negative ERG indicated an unexpected post-receptoral dysfunction, e.g. in cone (-rod) dystrophy or RP. The ON-bipolar pathway was affected in most cases.

Night blindness with depolarizing pattern of ON/OFF response in electroretinogram: a case report

PURPOSE

To present a patient who has night blindness with a depolarizing pattern of ON/OFF response by electroretinography (ERG).

CASE

A 43-year-old woman had had night blindness and poorly corrected visual acuity since childhood. Parental consanguinity was noted. The patient had suffered from mental retardation, epilepsy, and mild cerebellar ataxia. Corrected visual acuity was 20/30 in the right eye and 20/25 in the left. Goldmann perimetry showed no scotoma but slight depression with internal isoptors. No evidence for rod activity was observed by Goldmann-Weekers adaptometry. The ocular fundi appeared normal.

METHODS

Conventional full-field ERGs to scotopic (dim and bright flash) and photopic (bright flash and flicker) stimuli were recorded. Photopic ERG responses to long flash stimulation (200 ms) were also examined.

RESULTS

The scotopic responses to dim flash were non-recordable, while those to bright flash were severely reduced. The photopic responses to bright flash were decreased. The amplitudes of flicker responses also were significantly decreased, and the implicit times of those responses were prolonged. Although the amplitudes of a- and d-waves to long flash stimulation were reduced, those of the b-wave were within normal range. The implicit times of a-, b- and d-waves were significantly prolonged. The patient showed a normal rise for the photopic b-wave but lacked a normal falling slope after the b-wave peak. An OFF-response late-negativity was also noted.

CONCLUSIONS

The abnormal ON/OFF response found in the patient could be diagnosed as depolarizing pattern, characterized by elevation of the plateau to a positive potential above the prestimulus baseline. Since the ERG waveforms and clinical features found in our patient were different from those in previous reports, her ERG findings might reflect another retinal physiological mechanism.

LED-generated Multifocal ERG On- and Off-responses in Complete Congenital Stationary Night Blindness – A Case Report

We report on the application of a light emitting diode (LED) screen to elicit multifocal ERG on- and off-responses in a patient presenting with the complete type of congenital stationary night blindness (cCSNB): A 63-years old woman was diagnosed with cCSNB by means of standard ERG procedures and dark adaptometry. To confirm this diagnosis and to investigate topographical differences of on- and off-responses a multifocal approach employing long-duration stimuli was added. Results of mfERG-testing were averaged in three groups (a central area of 7.5 degrees , a ring area of 7.5-21.9 degrees and a peripheral ring of 21.9-31.1 degrees ). When compared to normal controls (n = 4) on-responses (P1-amplitudes) were severely reduced symmetrically at all eccentricities, while off-responses showed no reduction resulting in an increased off/on-ratio. Furthermore on-latencies of P1 were delayed symmetrically at all eccentricities, whereas off-latencies were normal. To our knowledge this is the first report of multifocal on- and off-responses in a CSNB-patient. Stimulus-generation with a LED-screen provides the advantage of a stable luminance during the long-duration on-phase.

Mutations in GRM6 cause autosomal recessive congenital stationary night blindness with a distinctive scotopic 15-Hz flicker electroretinogram

PURPOSE

Congenital stationary night blindness (CSNB) is a group of nonprogressive retinal disorders characterized by impaired night vision that occurs in autosomal dominant, autosomal recessive, or X-linked forms. Autosomal recessive (ar)CSNB seems to be very rare. Mice lacking the metabotropic glutamate receptor 6 (Grm6) have a defect in signal transmission from the photoreceptors to ON-bipolar cells. In the current study, the human orthologue (GRM6) was screened as a likely candidate for arCSNB.

METHODS

arCSNB individuals of five families were screened for mutations in GRM6. Subsequently, they were examined with standard and 15-Hz flicker electroretinography (ERG). These recordings were compared with those of patients with X-linked CSNB1.

RESULTS

Affected individuals in three of five families carried either compound heterozygous or homozygous mutations in GRM6. Strikingly, all of them displayed a distinctive abnormality of the rod pathway signals on scotopic 15-Hz flicker ERG.

CONCLUSIONS

The novel profile identified in this study suggests the existence of more than two rod pathways. The distinctive ERG feature was not observed in patients with X-linked CSNB1 and additional affected individuals with unknown molecular defect. These observations will help to discriminate autosomal recessive from X-linked recessive cases by ERG and molecular genetic analysis.

Photoreceptor calcium channels: Insight from night blindness

The genetic locus for incomplete congenital stationary night blindness (CSNB2) has been identified as the CACNA1f gene, encoding the α1F calcium channel subunit, a member of the L-type family of calcium channels. The electroretinogram associated with CSNB2 implicates α1F in synaptic transmission between retinal photoreceptors and bipolar cells. Using a recently developed monoclonal antibody to α1F, we localize the channel to ribbon active zones in rod photoreceptor terminals of the mouse retina, supporting a role for α1F in mediating glutamate release from rods. Detergent extraction experiments indicate that α1F is part of a detergent-resistant active zone complex, which also includes the synaptic ribbons. Comparison of native mouse rod calcium currents with recombinant α1F currents reveals that the current–voltage relationship for the native current is shifted approximately 30 mV to more hyperpolarized potentials than for the recombinant α1F current, suggesting modulation of the native channel by intracellular factors. Lastly, we present evidence for L-type α1D calcium channel subunits in cone terminals of the mouse retina. The presence of α1D channels in cones may explain the residual visual abilities of individuals with CSNB2.

A variant form of Oguchi disease mapped to 13q34 associated with partial deletion of GRK1 gene

PURPOSE

The purpose of this paper is to map the locus for a variant form of Oguchi disease in a Pakistani family and to identify the causative mutation.

METHODS

Family 61029 was ascertained in the Punjab province of Pakistan. It includes three 13- to 19-year-old patients with night blindness and 12 unaffected family members. A complete ophthalmological examination including fundus photography and electroretinography (ERG) was performed on each family member. A genome-wide scan was performed using microsatellite markers at about 10 cM intervals, and two-point lod scores were calculated. Polymerase chain reaction (PCR) cycle dideoxynucleotide sequencing was used to screen candidate genes inside the linked region for mutations and to delineate the deletion. Multiplex PCR and long template PCR were used to detect deletions and to define the size of deletions. Evaluation of fundus changes and ERG, lod score estimation, and identification of a mutation in the GRK1 gene were carried out.

RESULTS

All patients had night blindness since early childhood. Irregular coarse pigmentation was observed in the peripheral retina of each patient. The fundus appearance before and after 4 h of dark adaptation was similar except that the peripheral retinal pigmentary changes were slightly less evident after extended dark adaptation. Minimal or no rod function with normal cone function on ERG recordings were detected in all three affected members. The rod showed slow recovery to nearly normal amplitude after 4 h in the dark ERG in one individual but not in two other patients. A genome-wide scan showed linkage only to D13S285. Fine mapping defined a region from D13S1315 to 13qter, with a lod score of 2.89 at theta=0 shown by D13S285 and 2.90 at theta=0 by the D13S261-D13S285-D13S1295-D13S293 haplotype. Analysis of the GRK1 gene, which is included in this interval, identified a c.827+623_883del mutation. This intragenic deletion cosegregates with the disease in the family and is only homozygous in affected individuals. This mutation was not detected in 96 controls.

CONCLUSIONS

The retinal disease in the family reported here has several features differing from typical Oguchi disease, including an atypical Mizuo-Nakamura phenomenon and a non-recordable rod ERG even after 4 h of dark adaptation. Normal visual acuity, normal caliber of retinal blood vessels, and normal cone response on ERG recording suggest retinal dysfunction rather than degeneration (i.e., a variant form of Oguchi disease but unlikely to be retinitis pigmentosa). The disease in the Pakistani family localizes to 13q34 and is caused by a novel deletion including Exon 3 of the GRK1 gene.

A New Night Vision Disturbances Parameter and Contrast Sensitivity as Indicators of Success in Wavefront-guided Enhancement

PURPOSE

To determine the level of success of wavefront-guided repair of night vision disturbances after conventional (Munnerlyn) myopic LASIK using a new parameter to describe higher order aberrations, and to compare the improvements to matched myopic LASIK controls who were symptom-free.

METHODS

We developed a single parameter metric to represent raw spherical aberration (RAWS) to functionally describe the cumulative spherical aberration for an eye over a range of physiological pupil sizes. To derive the RAWS parameter, spherical aberration is plotted over pupil analysis zones from 3000 to 6000 microm. The RAWS parameter (unit = microm2) is then equal to the area under the plot. Sixteen eyes treated for night vision disturbances by wavefront-guided repair were each compared to the mean of four matched control eyes (total 64 eyes) treated by aspheric myopic ablation and without night vision disturbances. Contrast sensitivity and RAWs parameter for spherical aberration were determined for each of the repair eyes and control eyes before and after surgery.

RESULTS

Following wavefront-guided repair, 76% of eyes were subjectively reported to have night vision disturbances improved by at least 80%. The percentage of eyes within normal contrast range increased from 25% to 80% following wavefront-guided repair (P < .05). For the control eyes, LASIK increased RAWS by 126% (RAWS was 122 microm2 preoperatively and 276 microm2 postoperatively). For the night vision disturbances repair eye group, RAWS at presentation was 104% (563 microm2) above the respective postoperative RAWS control eyes. Following wavefront-guided repair, RAWS was decreased (P < .05) to only 49% (410 microm2) above the postoperative control group.

CONCLUSIONS

The RAWS parameter enabled a single digit descriptor of overall higher order aberrations for an eye over the principal physiological pupil range. By comparing RAWS parameter changes in wavefront-guided repair eyes to matched postoperative asymptomatic eyes, we were able to determine the magnitude of the deficit in the symptomatic eyes and the relative efficacy of wavefront-guided repair.

Pharmacological management of night vision disturbances after refractive surgery

PURPOSE

To evaluate the efficacy and safety of diluted aceclidine eyedrops in reducing night vision disturbances after refractive surgery.

SETTING

Department of Ophthalmology, Istituto Clinico Humanitas, Rozzano-Milano, Italy.

METHODS

This double-masked randomized clinical trial included 30 patients (60 eyes) with chronic night vision disturbance after refractive surgery. Patients were randomly allocated to receive (1) placebo, (2) aceclidine 0.016%, or (3) aceclidine 0.032%. Drugs were administered once or twice daily. Anterior segment, haze, uncorrected visual acuity, best corrected visual acuity, intraocular pressure, corneal maps, and scotopic pupil size were determined at baseline and at follow-up examinations (15 and 30 days after inclusion). Halos and double vision 4-step scales were built to determine subjective grading of night vision disturbance, and the root mean square (RMS) was calculated to determine objective changes in night vision disturbance.

RESULTS

The effect of diluted aceclidine started about 15 minutes after instillation and lasted for about 5 hours. No difference between the 2 dilutions could be found. Thirty-nine of 40 treated eyes showed a reduction in night vision disturbance. The mean reduction in halos and double vision grading was 1.42 +/- 0.5 (SD) and 1.14 +/- 0.4, respectively. A mean decrease in pupil size of 2.5 mm was measured. Thirty minutes after the instillation of diluted aceclidine, the topography-derived wavefront error showed a statistically significant reduction in RMS values (total, spherical, astigmatic, coma, and higher order), which was maintained for 5 hours. A transitory conjunctival hyperemia was the only side effect reported.

CONCLUSION

Diluted aceclidine seemed to be an effective and safe treatment for night vision disturbance following refractive surgery.

Congenital stationary night blindness type 2 mutations S229P, G369D, L1068P, and W1440X alter channel gating or functional expression of Ca(v)1.4 L-type Ca2+ channels

Mutations in the CACNA1F gene (voltage-dependent L-type calcium channel alpha1F subunit) encoding retinal Ca(v)1.4 L-type Ca2+ channels cause X-linked recessive congenital stationary night blindness type 2 (CSNB2). Many of them are predicted to yield nonfunctional channels. Complete loss of Ca(v)1.4 function is therefore regarded as a pathogenetic mechanism for the impaired signaling from photoreceptors to second-order retinal neurons. We investigated the functional consequences of CSNB2 missense mutations S229P, G369D, and L1068P and the C-terminal truncation mutant W1440X. After expression in Xenopus laevis oocytes or human embryonic kidney tsA-201 cells, inward Ca2+ current (I(Ca)) and inward Ba2+ current (I(Ba)) could be recorded from mutations G369D and L1068P. G369D shifted the half-maximal voltage for channel activation (V(0.5,act)) significantly to more negative potentials (>11 mV), slowed inactivation, and removed Ca2+-dependent inactivation. The L1068P mutant yielded currents only in the presence of the channel activator BayK8644. Currents (I(Ba)) inactivated faster than wild type (WT) and recovered more slowly from inactivation (I(Ba) and I(Ca)). No channel activity could be measured for mutants S229P and W1440X after oocyte expression. No W1440X alpha1 protein was detected after expression in tsA-201 cells, whereas S229P (as well as G369D and L1068P) alpha1 subunits were expressed at levels indistinguishable from WT (n = 3). Our data provide unequivocal evidence that CSNB2 missense mutations can induce severe changes in Ca(v)1.4 function, which may decrease (L1068P and S229P) or even increase (G369D) channel activity. The lower activation range of G369D can explain the reduced dynamic range of photoreceptor signaling. Moreover, we demonstrate that loss of channel function of one (L1068P) CSNB2 mutation can be rescued by a Ca2+ channel activator.

Cone and rod dysfunction in fundus albipunctatus with RDH5 mutation: an electrophysiological study

PURPOSE

A prior study showed that some patients with fundus albipunctatus (FA) have severely reduced full-field cone ERGs. The purpose of this study was to investigate the frequency of cone dysfunction and to determine the cause of the reduced full-field cone ERGs in patients with FA and whether the rod system is affected in patients with FA.

METHODS

Sixteen consecutive patients with FA (from 1993 to 2003; eight males, eight females; mean age, 25.4 years) with an RDH5 gene mutation were studied. The amplitudes and implicit times of the standard cone ERGs in the patients with FA were compared to those obtained from normal subjects (n = 55). The a-waves of cone ERGs were also elicited by a bright flash and were fitted to a mathematical model of the a-wave. Rod ERG responses were elicited by dim blue flashes after 3 hours of dark adaptation.

RESULTS

The amplitude of the b-wave of the cone ERG in the FA group varied considerably from within the normal limits to markedly decreased. Six of 16 patients with FA had b-wave amplitudes that were smaller than the lowest limit of the control subjects. The degree of cone dysfunction tended to be more severe in older patients. The analysis of the cone a-wave demonstrated that R(m) (maximal response amplitude) in the patients with FA with reduced standard cone ERGs was significantly smaller than that in control subjects. Rod ERGs were also reduced in the patients with FA who had reduced cone ERGs.

CONCLUSIONS

In patients with FA, 38% had extensive cone dysfunction. The reduced full-field cone ERGs were mainly due to the loss of cone photoreceptors, and the rod system was also affected in some patients.

A dominant form of congenital stationary night blindness (adCSNB) in a large Chinese family

Summary A pedigree of congenital stationary night blindness (CSNB) is described in a large Chinese family. The clinical description, pedigree, dark adaptation and elctroretinogram (ERG) studies indicate that the patients have an autosomal dominant form (ad) of CSNB. The disorder has been transmitted through at least 12 generations with over 40 affected individuals identified. The ERG data reveal that affected persons have severely diminished b-wave responses to dim light, but normal a-wave and subnormal b-wave responses to maximum light stimuli. The dark adaptation curves of three patients show a monophase curve, typical for night blindness. We have excluded the five previously known mutations in the three genes (RHO, PDE6B and GNAT1) associated with adCSNB, and linkage studies have excluded tight linkage between the disease locus and markers associated with these three genes. Thus, this family has adCSNB caused by a different gene from the previously identified RHO, PDE6B, and GNAT1.

Unique characteristics of two types of retinitis pigmentosa patients with different rod sensitivities

PURPOSE

To determine the psychophysical differences between two types of retinitis pigmentosa (RP) patients with different rod sensitivities.

METHODS

Thirty-five RP patients with a visual acuity of > or =0.7 or better were classified by cone-rod perimetry into type 1, those with undetectable rod sensitivity, and type 2, those with measurable rod sensitivity. Their symptoms, age at onset of symptoms, cone and rod sensitivity, and full-field electroretinograms (ERGs) were compared.

RESULTS

The age when the symptoms of night blindness were first noticed was 13.1 +/- 3.3 years (mean +/- SD) for type 1 and 34.5 +/- 14.4 years for type 2 patients (P = 0.0001). One of nine type 1 patients (11%) and 10 of 26 type 2 patients (38%) did not have any symptoms of night blindness. The average rod sensitivity within the central 10 degrees was 43.7 +/- 12.0 dB for type 2 patients with night blindness, and 54.8 +/- 6.4 dB for type 2 patients without night blindness (P = 0.014). One of nine (11%) type 1 patients and 9 of 23 (39%) type 2 patients had recordable ERGs (P = 0.13).

CONCLUSIONS

These findings indicate that the two types of RP patients, distinguished by their rod sensitivity, have different psychophysical characteristics of the visual system. The course of the disease process and the long-term prognosis for these two types of patients are different.