Low-noise electroretinogram recording techniques in retinitis pigmentosa

A proposal for an updated staging system for LCHADD retinopathy

OBJECTIVE

To develop an updated staging system for long-chain 3-hydroxyacyl coenzyme A dehydrogenase deficiency (LCHADD) chorioretinopathy based on contemporary multimodal imaging and electrophysiology.

METHODS

We evaluated forty cases of patients with genetically confirmed LCHADD or trifunctional protein deficiency (TFPD) enrolled in a prospective natural history study. Wide-field fundus photographs, fundus autofluorescence (FAF), optical coherence tomography (OCT), and full-field electroretinogram (ffERG) were reviewed and graded for severity.

RESULTS

Two independent experts first graded fundus photos and electrophysiology to classify the stage of chorioretinopathy based upon an existing published system. With newer imaging modalities and improved electrophysiology, many patients did not fit cleanly into a single traditional staging group. Therefore, we developed a novel staging system that better delineated the progression of LCHADD retinopathy. We maintained the four previous delineated stages but created substages A and B in stages 2 to 3 to achieve better differentiation.

DISCUSSION

Previous staging systems of LCHADD chorioretinopathy relied on only on the assessment of standard 30 to 45-degree fundus photographs, visual acuity, fluorescein angiography (FA), and ffERG. Advances in recordings of ffERG and multimodal imaging with wider fields of view, allow better assessment of retinal changes. Following these advanced assessments, seven patients did not fit neatly into the original classification system and were therefore recategorized under the new proposed system.

CONCLUSION

The new proposed staging system improves the classification of LCHADD chorioretinopathy, with the potential to lead to a deeper understanding of the disease's progression and serve as a more reliable reference point for future therapeutic research.

Advance in ERG analysis: from peak time and amplitude to frequency, power, and energy

Purpose. To compare time domain (TD: peak time and amplitude) analysis of the human photopic electroretinogram (ERG) with measures obtained in the frequency domain (Fourier analysis: FA) and in the time-frequency domain (continuous (CWT) and discrete (DWT) wavelet transforms). Methods. Normal ERGs (n = 40) were analyzed using traditional peak time and amplitude measurements of the a- and b-waves in the TD and descriptors extracted from FA, CWT, and DWT. Selected descriptors were also compared in their ability to monitor the long-term consequences of disease process. Results. Each method extracted relevant information but had distinct limitations (i.e., temporal and frequency resolutions). The DWT offered the best compromise by allowing us to extract more relevant descriptors of the ERG signal at the cost of lesser temporal and frequency resolutions. Follow-ups of disease progression were more prolonged with the DWT (max 29 years compared to 13 with TD). Conclusions. Standardized time domain analysis of retinal function should be complemented with advanced DWT descriptors of the ERG. This method should allow more sensitive/specific quantifications of ERG responses, facilitate follow-up of disease progression, and identify diagnostically significant changes of ERG waveforms that are not resolved when the analysis is only limited to time domain measurements.

Refractive surgery in patients with retinitis pigmentosa

PURPOSE

To evaluate the refractive outcomes and safety of laser refractive surgery in a group of myopic patients with retinitis pigmentosa (RP).

METHODS

This was a multicenter, retrospective, noncomparative, interventional case series. A total of 32 eyes of 16 patients with RP with at least 18 months of follow-up were treated with laser refractive surgery (photorefractive keratectomy [PRK], laser subepithelial keratectomy [LASEK]). Refractive outcomes, complete eye examination, corneal topography, and retinal sensitivities were evaluated during follow-up. Mean follow-up was 28.3 months (minimum 18, maximum 50). Mean patient age was 29.6 years (range 24-54). Mean best-corrected visual acuity (BCVA) was 0.75 preoperatively.

RESULTS

Eighteen months after surgery, mean uncorrected visual acuity (UCVA) was 0.8+/-1 line (p=0.02); mean BCVA was 0.85+/-1 line (p<0.0005) with mean spherical equivalent of -0.16 D. Corneal complications were not detected during follow-up; corneal topography did not show corneal ectasia in any patient after surgery. During follow-up visits, no development or progress of macular edema was noted in any eye. Retinal sensitivities increased after surgery; there were no significant changes in electroretinogram amplitude.

CONCLUSIONS

Mean UCVA and BCVA 18 months after surgery were higher than preoperative BCVA. All patients were safely treated without any significant complications. Our results support the safety of performing PRK and LASEK in patients with tapetoretinal degeneration.

Slowing the degenerative process, long lasting effect of hyperbaric oxygen therapy in retinitis pigmentosa

BACKGROUND

Retinitis pigmentosa (RP) therapy is still an unsolved challenge. Recent reports have underlined that hyperbaric oxygen (HBO) therapy could play a role in slowing the retinal degenerative process. The aim of this study was to assess the efficacy of HBO therapy on visual function in RP patients.

METHODS

We performed a single-center, comparative, longitudinal case-controlled randomized clinical trial, which lasted 10 years. We randomly divided RP patients into two groups. Group 1, the control group, consisted of 44 RP patients (21 males and 23 females; mean age 35.5) who took Vitamin A. Group 2, with 44 RP patients (21 males and 23 females; mean age 35,02), underwent HBO therapy. No statistically significant difference was found at the beginning of the study between the two groups. We compared the results concerning visual acuity, Goldmann perimetry, static perimetry Humphrey field analyzer (HFA), and electroretinogram (ERG) obtained in the two groups at 5 and 10 years follow-up. Statistical analysis was performed with Kaplan-Meier life-table with the evaluation of log-rank coefficient.

RESULTS

At 5 year follow-up, 87.5% of group 2 patients preserved 80% of the initial visual acuity, while the same result was achieved in only 70.4% of group 1 patients (X(2) = 8.2; p < 0.01); at 10 year follow-up, 63.33% of group 2 patients preserved 80% of the initial visual acuity, while the same percentage of residual visual acuity was maintained in 40% of group 1 patients (X(2) = 3.22; p = 0.05). At 10 year follow-up, Goldmann perimetry (target I4e) did not change in 31.6% of group 2 and in 10.5% of group 1; evaluation of mean defect (MD) with static perimetry HFA showed that 53% of HBO patients had 80% of residual mean sensitivity compared to 23.5% of the control group patients (X(2) = 4.72; p = 0.035). ERG b-wave mean values at the end of the protocol were significantly higher in the HBO treated group (X(2) = 4.53; p = 0.013).

CONCLUSION

Our study underlines that HBO therapy can be a safe alternative approach to RP patients, contributing to the stabilization of their visual function concerning visual acuity, visual field, and ERG responses while waiting for a definite cure.

Retinitis pigmentosa associated with rhodopsin mutations: Correlation between phenotypic variability and molecular effects

Similar retinitis pigmentosa (RP) phenotypes can result from mutations affecting different rhodopsin regions, and distinct amino acid substitutions can cause different RP severity and progression rates. Specifically, both the R135L and R135W mutations (cytoplasmic end of H3) result in diffuse, severe disease (class A), but R135W causes more severe and more rapidly progressive RP than R135L. The P180A and G188R mutations (second intradiscal loop) exhibit a mild phenotype with regional variability (class B1) and diffuse disease of moderate severity (class B2), respectively. Computational and in vitro studies of these mutants provide molecular insights into this phenotypic variability.

Does hyperbaric oxygen (HBO) delivery rescue retinal photoreceptors in retinitis pigmentosa?

As previously reported in the literature, hyperbaric oxygen delivery seems to modify the natural course of retinitis pigmentosa. In order to evaluate these first encouraging data, 48 affected subjects were separately studied in two subgroups (cases and controls). All patients underwent yearly an ophthalmological examination completed by a maximum amplitude electroretinogram, conducted according to our 'differential derivation' system, a new recording technique specifically designed to enhance the signal-to-noise ratio. Oxygen delivery was provided regularly for 90 min daily (2.2 Absolute Atmosphere) in three cycles according to a standard protocol. In the cases, electroretinographic mean values were as follows: at T0 (basal) 4.68 +/- 3.81 microV; after one year (T1) 8.46 +/- 5.71 microV; at two years (T2) 10.7 +/- 7.6 microV; at the end of the study (T3) 14.4 +/- 11.7 microV. In the controls, electroretinographic mean values were as follows: at T0 4.92 +/- 3.05 microV; at T1 5.04 +/- 3.07 microV; at T2 3.46 +/- 2.77 microV: at T3 2.97 +/- 3.61 microV. Amplitudes showed a remarkable (p<0.001) increase in the cases, while a slightly significant (p<0.02) decrease was evident at the end of the study in the controls. In our opinion, retinal oxygen availability may be critical in retinal degeneration and hyperbaric oxygen delivery, inducing hyperoxia, seems to be able to bring about the rescue of the retinal photoreceptors helping them in their metabolic requirements. Unfortunately, our study demonstrates an increase in electroretinographic responses only, which may not necessarily also mean an evident change in visual acuity.

The ocular phenotype of the Bardet-Biedl syndrome. Comparison to non-syndromic retinitis pigmentosa

PURPOSE

To investigate 20 patients affected with Bardet-Biedl (BB) syndrome and compare them to an age-matched group of 70 non-syndromic patients with retinitis pigmentosa (RP) to identify hallmarks peculiar to the BB phenotype.

METHODS

Patients were examined clinically and with functional tests (color vision, kinetic perimetry, electroretinography, ocular motility tests). Fundus findings were numerically graded for statistical purposes.

RESULTS

Recurrent ocular features in BB patients were early and severe reduction of visual acuity, constantly altered color vision, high incidence of strabismus and nystagmus, mild-to-severe atrophic changes of the optic disc, and frequently absent or minimal pigmentary retinal changes. Visual acuity was more closely correlated to optic disc than to macular conditions. These findings were remarkably different from non-syndromic RP.

CONCLUSIONS

This investigation further suggests that retinopathy in BB syndrome has features distinctive from those in non-syndromic RP. The early occurrence of optic disc atrophy in the BB syndrome, even in those patients with healthy maculas, suggests that optic atrophy could often be primary in nature and might play a major role in decreasing central vision in BB patients. Variability of some findings is in line with the documented heterogeneity of the BB syndrome.

Autosomal-dominant retinitis pigmentosa associated with an Arg-135-Trp point mutation of the rhodopsin gene. Clinical features and longitudinal observations

PURPOSE

To report the clinical and functional characteristics of patients affected with autosomal-dominant transmitted retinitis pigmentosa (adRP) from a large Italian pedigree in which a point mutation predicting the Arg-135-Trp change of rhodopsin was identified by polymerase chain reaction-single-strand conformation polymorphism analysis.

METHODS

Seven patients, ranging in age from 6 to 41 years, underwent a full clinical ophthalmologic evaluation, kinetic visual field testing, and electroretinographic testing.

RESULTS

In agreement with previous reports, this rhodopsin mutation yielded a particularly severe phenotype, both clinically and functionally. The evaluation of patients from this pedigree in the first and second decade of life demonstrated that retinal function is still electroretinographically measurable at least until 18 years of age, although reduced to 2% to 4% of normal. Longitudinal measures showed that the rate of progression of the disease was unusually high, with an average 50% loss per year of electroretinographic amplitude and visual field area with respect to baseline. Later in the course of the disease, macular function is also severely compromised, leaving only residual central vision by the fourth decade of life.

CONCLUSIONS

The phenotype associated with mutations in codon 135 of the rhodopsin molecule appears to have an unusually high progression rate and yields an extremely poor prognosis. These distinctive features make the Arg-135-Trp phenotype substantially different from the general RP population, and also from many of the other adRP pedigrees with known rhodopsin mutations reported to date.

Electroretinographic alterations in the Laurence-Moon-Bardet-Biedl phenotype

Maximal 0.5-Hz and cone 30-Hz ERG responses were recorded from 19 patients showing a Laurence-Moon-Bardet-Biedl (LMDD) phenotype. Off-line averaging of 80 to 100 iterations was routinely performed. When needed, our previously described low-noise techniques and off-line fast Fourier transform procedures were used. The maximal ERG response was non-detectable in 52.6% of cases. About half of the recordable signals were below 5% of the lower normal amplitudes. Cone 30-Hz ERGs were measurable in 64.7% of cases. Of these, 63% of tracings were below 5% of the lower normal range. In most cases no dystrophic pattern was definable, due to severe reduction of both signals. Statistical analyses showed no correlation between ERG amplitudes and residual visual field areas. Clinical and electroretinographic observations suggest that retinopathy in most LMBB patients is a widespread form of degeneration, initially affecting rods but rapidly involving cones as well. However, there are also cases with a clear-cut cone-rod pattern, with fairly well preserved maximal ERG responses. The lack of correlation between maximal ERG responses and visual field residual areas, different from non-syndromic retinitis pigmentosa (RP) patients, could be related either to a low reliability of visual field testing in LMBB patients or to mechanisms accounting for the ongoing retinal degeneration in LMBB syndrome that are different from those of pure RP. Variable findings are in line with the documented genetic heterogeneity of the syndrome.

Correlation between Goldmann perimetry and maximal electroretinogram response in retinitis pigmentosa

To evaluate the relationship between Goldmann perimetry and maximal electroretinographic responses in patients with retinitis pigmentosa, analyses were performed on 220 affected subjects and separately on two subgroups with autosomal dominant (n = 35) and autosomal recessive (n = 29) inheritance. Electroretinograms were recorded averaging 100 iterations elicited with a 20-lux/s, 0.5-Hz white flash ganzfeld stimulation. The peripheral isopters of the visual fields were delimited with I4e, IIIe and V4e targets, measured on conventional perimetry charts with a light pen and expressed in square centimeters. Unlike most previously published reports, this investigation showed a definite correlation (p = 0.0001) between maximal electroretinographic response amplitude and visual field areas. This correlation was more evident for I4e and IIIe isopters (r = 0.89 and 0.87, respectively) than for V4e isopter (r = 0.69). This phenomenon appears to be related to distortion occurring on standard isometric charts and to spatial summation effects in the peripheral field. Such correlations held for both the autosomal dominant and autosomal recessive subgroups. It appears that, if enough accuracy is provided, maximal electroretinographic responses and Goldmann visual fields are both good measures of the remaining functioning retina in nonsyndromic retinitis pigmentosa, irrespective of inheritance models and dystrophic patterns.