[Studies of the distribution of lipofuscin in the retinal pigment epithelium using high-resolution TV laser scanning ophthalmoscopy]

BACKGROUND

The fundus autofluorescence imaging technique has been modified allowing improved image resolution (768 x 572 pixel). We present results of fundus autofluorescence studies using this technique.

MATERIALS AND METHODS

Fundus autofluorescence was studied in 286 eyes of 143 patients with retinitis pigmentosa, macular dystrophies and age-related macular degeneration using a confocal laser scanning ophthalmoscope prototype (Zeiss, Oberkochen; excitation wavelength: 488 nm, cut-off filter at 521 nm).

RESULTS

The spatial distribution of autofluorescence was different in all diseased eyes investigated compared to the normal pattern of fundus autofluorescence. Each disorder showed a specific fundus autofluorescence appearance.

CONCLUSIONS

The advanced technique of imaging fundus autofluorescence allows detailed studies of the lipofuscin distribution. In vivo analysis of the dynamics of accumulation and degradation of lipofuscin in eyes with tapeto-retinal dystrophies and age-related macular disease may contribute to elucidation of the pathogenesis of these disorders.

Further refinement of the Usher 2A locus at 1q41

Usher syndrome (USH) is characterised by congenital sensorineural hearing loss and progressive pigmentary retinopathy. All three subtypes (USH1, USH2, and USH3) are inherited as recessive traits. People with Usher type 2 (USH2) have normal vestibular responses and moderate to severe hearing loss. These syndromes have been found to be genetically heterogeneous, with a single locus for USH2 at 1q41 (USH2A), six loci for USH1, and one for USH3. Some USH2 families have been excluded from the 1q41 locus suggesting that a second, as yet unidentified, locus (USH2B) must exist. Linkage studies suggest that around 90% of USH2 families are USH2A. Four USH2 families were analysed for linkage to markers flanking the USH2A locus. In one of these families a recombination event was observed in an affected subject which excludes the USH2A gene from proximal to the marker AFM143XF10 and defines this as the new centromeric flanking marker for the USH2A locus. A further recombination event in another patient from this family confirmed AFM144XF2 as the telomeric flanking marker. The interval between these polymorphic markers is estimated to be 400 kb. This region is completely contained in each of three YACs from the CEPH library: 867g9, 919h3, and 848b9. This refinement more than halves the critical genetic interval and will greatly facilitate positional cloning of the USH2A gene.

A new dominant retinitis pigmentosa family mapping to the RP18 locus on chromosome 1q11-21

Images

[Fundus autofluorescence in patients with hereditary macular dystrophies, malattia leventinese, familial dominant and aged-related drusen]

PURPOSE

The lack of histopathological material has placed limitation on our knowledge on the composition of focal deposits in eyes with macular dystrophies, malattia leventinese, dominant drusen and age related macular degeneration. This study was designed to study the composition of focal deposits in these eyes by documenting fundus autofluorescence in vivo.

METHODS

Fundus autofluorescence was documented in 343 eyes of 199 subjects with macular dystrophies, malattia leventinese, dominant drusen and age-related macular degeneration using a laser scanning ophthalmoscope (Zeiss, Oberkochen; excitation wavelength: 488 nm, barrier filter at 521 nm).

RESULTS

Autofluorescence of focal deposits was increased in eyes with macular dystrophies. In eyes with malattia leventinese and dominant drusen autofluorescence intensity of focal deposits showed a wide spectrum. In contrast, autofluorescence of age-related drusen was within normal limits. Background autofluorescence intensity was increased in eyes with macular dystrophies and within normal limits in eyes with malattia leventinese, dominant drusen and age-related drusen.

CONCLUSION

The technique of in-vivo recording of fundus autofluorescence allows the differential diagnosis between macular dystrophies/malattia leventinese, dominant drusen/age related drusen when otherwise not possible.

Fruits and vegetables that are sources for lutein and zeaxanthin: the macular pigment in human eyes

BACKGROUND

It has been suggested that eating green leafy vegetables, which are rich in lutein and zeaxanthin, may decrease the risk for age related macular degeneration. The goal of this study was to analyse various fruits and vegetables to establish which ones contain lutein and/or zeaxanthin and can serve as possible dietary supplements for these carotenoids.

METHODS

Homogenates of 33 fruits and vegetables, two fruit juices, and egg yolk were used for extraction of the carotenoids with hexane. Measurement of the different carotenoids and their isomers was carried out by high performance liquid chromatography using a single column with an isocratic run, and a diode array detector.

RESULTS

Egg yolk and maize (corn) contained the highest mole percentage (% of total) of lutein and zeaxanthin (more than 85% of the total carotenoids). Maize was the vegetable with the highest quantity of lutein (60% of total) and orange pepper was the vegetable with the highest amount of zeaxanthin (37% of total). Substantial amounts of lutein and zeaxanthin (30-50%) were also present in kiwi fruit, grapes, spinach, orange juice, zucchini (or vegetable marrow), and different kinds of squash. The results show that there are fruits and vegetables of various colours with a relatively high content of lutein and zeaxanthin.

CONCLUSIONS

Most of the dark green leafy vegetables, previously recommended for a higher intake of lutein and zeaxanthin, have 15-47% of lutein, but a very low content (0-3%) of zeaxanthin. Our study shows that fruits and vegetables of various colours can be consumed to increase dietary intake of lutein and zeaxanthin.

Mutations in the retinal guanylate cyclase (RETGC-1) gene in dominant cone-rod dystrophy

The dominant cone-rod dystrophy gene CORD6 has previously been mapped to within an 8 cM interval on chromosome 17p12-p13. The retinal-specific guanylate cyclase gene (RETGC-1), which maps to within this genetic interval and previously was implicated in Leber's congenital amaurosis, was screened for mutations within this family and in a panel of small families and individuals with various cone and cone- rod dystrophy phenotypes. A missense mutation (E837D) was identified in affected members of the CORD6 family, as well as a second missense mutation (R838C) in three other families with dominant cone-rod dystrophy. RETGC-1 is only the fourth gene to be implicated in cone-rod dystrophy and this is the first report of dominant mutations in this gene.

[Dynamics of accumulation and degradation of lipofuscin in retinal pigment epithelium in senile macular degeneration]

BACKGROUND

It is thought that lipofuscin plays a central role in the pathogenesis of age-related macular degeneration (AMD). The lack of histopathological material has been a severe limitation in our knowledge on lipofuscin in this disease. A new technique has been developed that allows in vivo imaging of fundus autofluorescence derived from lipofuscin in the retinal pigment epithelium (RPE) using a confocal Laser Scanning Ophthalmoscope (LSO). We studied the dynamics of lipofuscin accumulation and degradation in patients with AMD.

MATERIALS AND METHODS

Serial examinations of the spatial distribution of fundus autofluorescence were performed in 148 eyes of 74 patients with AMD using a LSO over a period of 1-3.5 years.

RESULTS

Fundus autofluorescence changed over time in almost all eyes studied. Areas of increased autofluorescence occurred progressively during follow up in eyes with drusen and hyperpigmentation. The size of pathologic autofluorescence increased over time in almost all eyes with geographic atrophy, subretinal neovascularisations and disciform scars. Irregular autofluorescence was seen over most subretinal neovascularisations. Autofluorescence intensity decreased in old subretinal neovascularisations and disciform scars over time.

CONCLUSIONS

Changes of the distribution of autofluorescence occur in eyes with AMD over time. Fundus autofluorescence imaging allows in vivo analysis of the dynamics of accumulation and degradation of lipofuscin in the RPE in eyes with AMD and documentation of metabolic activity of the RPE.

Prophylactic laser treatment to fellow eyes of unilateral retinal pigment epithelial tears

PURPOSE

To evaluate prophylactic laser treatment of the macula in reducing the risk of visual loss in the fellow eye of patients with a retinal pigment epithelial tear caused by age-related macular degeneration in the first eye.

METHODS

In a prospective study, 12 patients with a retinal pigment epithelial tear in one eye caused by age-related macular degeneration and drusen in the fellow eye received prophylactic laser treatment of the retina in their fellow eyes and were followed up for 2 years or more after prophylactic treatment.

RESULTS

In 12 fellow eyes that received prophylactic laser treatment, a reduction in best-corrected visual acuity to 20/80 or worse occurred in one (8%) of 12 eyes in the first year and two (18%) of the remaining 11 eyes in the second year after treatment. The cumulative risk of visual loss in the treated fellow eye was 25% in 2 years.

CONCLUSIONS

In historical control subjects in a natural history study of patients with retinal pigment epithelial tear in one eye, central visual loss occurred in 16 (37%) of 43 eyes in the first year and in seven (30%) of 23 eyes in the second year for a cumulative loss of 59% in the first 2 years. Compared with these historical control subjects, our findings suggest that visual loss in the fellow eyes of patients with a retinal pigment epithelial tear in the first eye is reduced by prophylactic low intensity laser photocoagulation of the macula.

Helicoidal peripapillary chorioretinal degeneration: electrophysiology and psychophysics in 17 patients

AIMS

To characterise retinal function using electrophysiological and psychophysical tests in 17 patients with helicoidal peripapillary chorioretinal degeneration.

METHODS

The electroretinogram (ERG) was recorded using gold foil corneal electrodes. The electro-oculogram (EOG) was recorded using a standard protocol. Dark adaptometry was recorded with an SST-1 dark adaptometer and colour vision assessed with Ishihara plates and Farnsworth D-15.

RESULTS

All subjects had a recordable ERG. The amplitudes and implicit times of the a- and b-waves were within normal limits at all luminances in five subjects (age 21-70 years, mean 40 years). The ERG of six (age 26-55 years, mean 40.7 years) had subnormal amplitudes at all luminances, but normal implicit times, and six (age 38-81 years, mean 60.7 years) had abnormal ERGs with marked reduction of a- and b-waves, and delayed implicit times of the b-wave. The implicit times of the a-wave were normal in all subjects. A reduction in the b/a wave ratios was not found, nor was there selective loss of scotopic, mixed rod/cone, or cone responses. The light/dark ratio of the EOG was subnormal (150-185%) or abnormal (below 150%) in all but three subjects. Two patients with normal EOG showed normal ERGs in both eyes, but one had subnormal ERGs in both eyes. The scotopic sensitivity was normal in all subjects and dark adaptation showed a normal time course. Colour vision was normal in all patients.

CONCLUSION

The results suggest that in most cases the function of the retinal pigment epithelium is affected by this disease before any changes in the function of the sensory retina are detectable by our methods, and that retinal dysfunction is focal rather than diffuse.

A mutation in guanylate cyclase activator 1A (GUCA1A) in an autosomal dominant cone dystrophy pedigree mapping to a new locus on chromosome 6p21.1

We report a mutation (Y99C) in guanylate cyclase activator 1A (GUCA1A), the gene for guanylate cyclase activating protein (GCAP1), in a family with autosomal dominant cone dystrophy. Linkage analysis excluded all the known cone and cone-rod dystrophy loci, except the chromosome 6p21.1 region. This is known to contain the RDS gene, which is associated with dominant cone-rod dystrophy. Screening of the RDS gene by heteroduplex analysis and direct sequencing failed to demonstrate sequence changes in the coding region of this gene. The gene for GCAP1, a calcium binding protein which is highly expressed in photoreceptor outer segments, is also located in 6p21.1. It was screened for mutations, and all affected individuals showed a single base pair missense mutation (A-->G) at codon 99 in exon 2 of this gene generating a tyrosine-to-cysteine change in the GCAP1 protein. This change was absent from 206 unrelated normal controls. We propose that this change would at least disrupt the EF3handof GCAP1 thereby preventing calcium binding and consequently interfere with activation. The resulting effect on cGMP production would predictably modify the number of open cGMP gated cation channels, and could explain the ultimate demise of cone photoreceptor cells.

A linkage survey of 20 dominant retinitis pigmentosa families: frequencies of the nine known loci and evidence for further heterogeneity

Autosomal dominant retinitis pigmentosa (ADRP) is caused by mutations in two known genes, rhodopsin and peripherin/Rds, and seven loci identified only by linkage analysis. Rhodopsin and peripherin/Rds have been estimated to account for 20-31% and less than 5% of ADRP, respectively. No estimate of frequency has previously been possible for the remaining loci, since these can only be implicated when families are large enough for linkage analysis. We have carried out such analyses on 20 unrelated pedigrees with 11 or more meioses. Frequency estimates based on such a small sample provide only broad approximations, while the above estimations are based on mutation detection in much larger clinic based patient series. However, when markers are informative, linkage analysis cannot fail to detect disease causation at a locus, whereas mutation detection techniques might miss some mutations. Also diagnosing dominant RP from a family history taken in a genetic clinic may not be reliable. It is therefore interesting that 10 (50%) of the families tested have rhodopsin-RP, suggesting that, in large clearly dominant RP pedigrees, rhodopsin may account for a higher proportion of disease than had previously been suspected. Four (20%) map to chromosome 19q, implying that this is the second most common ADRP locus. One maps to chromosome 7p, one to 17p, and one to 17q, while none maps to 1cen, peripherin/Rds, 8q, or 7q. Three give exclusion of all of these loci, showing that while the majority of dominant RP maps to the known loci, a small proportion derives from loci yet to be identified.

Localization of CSNBX (CSNB4) between the retinitis pigmentosa loci RP2 and RP3 on proximal Xp

PURPOSE

Proximal Xp harbors many inherited retinal disorders, including retinitis pigmentosa (RP) and congenital stationary night blindness, both of which display genetic heterogeneity. X-linked congenital stationary night blindness (CSNBX) is a nonprogressive disease causing night blindness and reduced visual acuity. Distinct genetic loci have been reported for CSNBX at Xp21.1, which is potentially allelic with the RP3 gene, and at Xp11.23, which is potentially allelic with the RP2 gene. The study to identify the RP2 gene led to an extended study of families with potentially allelic diseases that include CSNBX.

METHODS

Haplotype analysis of a family diagnosed with CSNBX was performed with 17 polymorphic markers on proximal Xp covering previously identified loci for CSNBX and XLRP. Two-point and multipoint lod scores were calculated.

RESULTS

Informative recombinations in this family define a locus for CSNBX (CSNB4) with flanking markers DXS556 and DXS8080 on Xp11.4 to Xp11.3, an interval spanning approximately 5 to 6 cM. A maximum lod score of 3.2 was calculated for the locus order DXS556-1 cM-(CSNB4-DXS993)-2 cM-DXS1201.

CONCLUSIONS

The results describe a new localization for CSNBX (CSNB4) between the RP2 and RP3 loci on proximal Xp. CSNB4 is not allelic with any previously reported XLRP loci; however, the interval overlaps the locus reported to contain the cone dystrophy (COD1) gene, and both diseases are nonrecombinant with DXS993. Because mutations in the RPGR gene to date account for disease in only a small proportion of RP3 families, the possibility that this new locus (CSNB4) also segregates with an as yet unidentified XLRP locus cannot be excluded.

Relationship between melatonin rhythms and visual loss in the blind

Melatonin rhythms were assessed in 49 registered blind individuals by measurement of the urinary metabolite of melatonin, 6-sulfatoxymelatonin (aMT6s). Subjects had different causes of visual loss and were classified as having light perception or better (LP; n = 19) or having no perception of light (NPL; n = 30). Subjects collected four-hourly urine samples (eight-hourly overnight) for 48 h at weekly intervals for 3-5 weeks. The majority of LP subjects (14 of 19) had normally entrained aMT6s rhythms (mean acrophase range, 2.4-6.2 h), 4 were abnormally entrained to 24 h (mean acrophase range, 8.9-1.0 h), and 1 was unclassified. Conversely, most NPL subjects had abnormal rhythms (23 of 30), the incidence of which was greater in uni- and bilaterally enucleated subjects. The majority of NPL subjects (17 of 30) had free-running aMT6s rhythms period range, 24.13-24.79 h), 5 were abnormally entrained to 24 h (acrophase range, 7.2-20.6 h), and 1 was unclassified. Output (micrograms of aMT6s per 24 h) and amplitude (micrograms per h) of aMT6s production did not vary between LP and NPL subjects (mean 24-h output +/- SD, 12.7 +/- 7.5 and 9.4 +/- 6.4 micrograms aMT6s/24 h, respectively; mean amplitude +/- SD, 0.6 +/- 0.4 and 0.5 +/- 0.3 microgram/h, respectively). These results indicate that a higher proportion of NPL subjects have abnormal melatonin rhythms compared to those with LP.

Assessment of the phenotypic range seen in Doyne honeycomb retinal dystrophy

OBJECTIVE

Using molecular genetics as the basis for diagnosis, to assess the phenotype in the family originally described as having dominantly inherited Doyne honeycomb retinal dystrophy (DHRD) linked to chromosome 2p16.

DESIGN

Clinical examination including fluorescein angiography was undertaken in 107 family members. Nine affected patients underwent electroretinography, perimetry, dark adaptometry, color-contrast sensitivity measurement, and autofluorescent fundus imaging.

PATIENTS

The disease-associated haplotype used to allocate disease status was based on our further refinement of the DHRD locus to between loci D2S2739 and D2S378. The study identified 50 affected patients. In addition, previously published information on a further 8 individuals was used. The study population represented 6 generations of a 9-generation pedigree.

RESULTS

Three types of deposits were seen: large, soft drusen at the macula and abutting the optic nerve head; small, hard deposits that in some patients radiated from the macula; and autofluorescent deposits. Most younger affected individuals exhibited small hard drusen only at the macula and had normal visual function. Information on 2 patients suggested that DHRD can be a cause of childhood-onset blindness. Advanced disease was associated with severe visual loss and posterior pole atrophy without signs of drusen. Advanced age was not invariably associated with severe visual loss.

CONCLUSIONS

Previously identified characteristics of DHRD were confirmed and new features identified. Contrary to previous reports, the constancy and severity of radial (basal laminar) drusen seen clinically are the only features that can be used to differentiate between DHRD and malattia leventinese. The highly variable phenotype suggests that the influence of the DHRD-mutant gene may be modulated by other genetic and/or environmental factors.

Laser treatment in subjects with high-risk clinical features of age-related macular degeneration. Posterior pole appearance and retinal function

OBJECTIVES

To verify that a few laser lesions in the posterior pole can cause drusen to resolve in patients with age-related macular degeneration, and to document central retinal sensitivity as drusen resolve.

DESIGN

In a pilot study, 12 patients considered to be at high risk for sight-threatening complications from age-related macular degeneration were treated with 12 argon laser lesions in the posterior pole, with review for 12 to 24 months.

RESULTS

Choroidal neovascularization developed in 1 patient 8 months after treatment, with consequent loss of central vision. In 9 of the remaining 11 patients, high-risk characteristics of drusen were reduced. Four patients had retinal pigment epithelial depigmentation, and all maintained 20/40 visual acuity at 12 months. One patient lost 3 lines of vision due to geographic atrophy after 12 months. Scotopic retinal threshold was elevated before treatment in 8 patients, compared with an age-matched comparison group. Of these, 4 patients underwent retesting 3 to 6 months after treatment, and all had improved thresholds, but only 1 patient sustained the improvement at 12 months. At 12 months, 3 of the 8 patients showed an improvement in their mean retinal threshold. Of those in whom the mean retinal threshold worsened, the mean elevation in threshold was not more than 0.6 log units.

CONCLUSIONS

A few laser lesions in the posterior pole leads to resolution of drusen. There does not appear to be an increased risk for choroidal neovascularization. Retinal threshold measurements show no indication of geographic atrophy at 1 year, but cannot be excluded as a late outcome. Laser treatment may reduce the risk for profound sight-threatening lesions in age-related macular degeneration.

Age-related macular disease in rural southern Italy

OBJECTIVE

To report the prevalence of age-related maculopathy (ARM) in Salandra, a small, isolated southern Italian community, to test the hypothesis that an environmental factor, scarce in such a remote community but ubiquitous in modern industrial societies, might modify the risk of developing ARM.

DESIGN

Population-based cross-sectional survey.

MAIN OUTCOME MEASURES

Prevalence of advanced age-related macular degeneration (ARMD) (geographic atrophy or exudative maculopathy) and ARM (large, soft drusen or retinal pigment epithelium changes, or both) defined by fundus biomicroscopy and 30 degrees stereoscopic, macular photography. Self-sustenance was assessed by interview of participants and local shop retailers. The degree of genetic isolation was computed using a model that fits the genetic population structure with the frequency distribution of surnames in the community.

RESULTS

A full ophthalmic examination was undertaken in 366 (63.5%) of 576 eligible participants, 354 (96.7%) of whom had clinical or photographic assessment for the presence of ARMD and 310 (84.6%) of whom had drusen characteristics graded on color transparencies for ARM. The overall prevalence of ARMD was 1.1%. Drusen larger than 50 microns and more numerous than 10 were found in 4.5% of subjects. Salandra was the birthplace of 87.2% of participants and for 77.3% of both parents of each subject. People in the community tended to consume homegrown products.

CONCLUSION

The prevalence of ARM may be lower in this self-sustained farming community than elsewhere in the industrialized world.

In vivo fundus autofluorescence in macular dystrophies

OBJECTIVE

To document the deviation from normal of fundus autofluorescence in patients with inherited macular dystrophies.

METHODS

The intensity and spatial distribution of fundus autofluorescence was documented in 118 patients with inherited macular dystrophies by means of a confocal laser scanning ophthalmoscope, and the images were compared with the fundus appearance and fluorescein angiograms.

RESULTS

Background autofluorescence appears to be elevated in all forms of macular dystrophies examined. The pale deposits at the level of the retinal pigment epithelium in disorders such as Best disease, adult vitelliform macular dystrophy, and fundus flavimaculatus were consistently associated with higher levels of autofluorescence than the background signal. There was no strong correlation between the intensity of autofluorescence and the fluorescein angiographic sign of a dark choroid. Increased levels of autofluorescence were present in a subject with a mutation known to cause macular dystrophy but in whom there were no manifest ophthalmoscopic or functional abnormalities.

CONCLUSIONS

All dystrophies examined have in common accumulation of autofluorescent material in the retinal pigment epithelium to a greater degree than that seen with age. The abnormal high background autofluorescence associated with inherited macular dystrophies confirms the impression derived from histological studies that these disorders affect the entire retinal pigment epithelium. The lack of correlation between autofluorescence and the presence of a dark choroid implies that there may be different fluorophores in different disorders. The pale deposits at the level of the retinal pigment epithelium-Bruch membrane seen in macular dystrophies have similar autofluorescence characteristics. This technique may be useful in detecting the abnormal phenotype in early disease.

Localisation of a gene for dominant cone-rod dystrophy (CORD6) to chromosome 17p

We have performed genetic linkage analysis on a four generation British family with cone-rod dystrophy. Significant linkage to the disease gene was obtained with eight marker loci situated on chromosome 17p12-p13. A maximum two-point lod score of 5.93 with no recombination was obtained with marker locus D17S1844. Critical recombinants identified with flanking marker loci placed the disease gene between D17S796/D17S938 and D17S954, an interval estimated to be 8 cM in size. This new localisation for autosomal dominant cone-rod dystrophy (CORD6) overlaps with regions attributed previously to Leber's congenital amaurosis, central areolar choroidal dystrophy and dominant cone dystrophy. Given their differences in phenotype, the most plausible explanation would be that these different retinal disorders are caused by mutations in different genes mapping close together within the genome.

Fundus autofluorescence in age-related macular disease imaged with a laser scanning ophthalmoscope

PURPOSE

To image and quantify the spatial distribution of fundus autofluorescence in normal subjects, to determine its age dependence, and to document the deviation from normal in patients with age-related macular disease.

METHODS

Using a confocal laser scanning ophthalmoscope (cLSO), the intensity and spatial distribution of fundus autofluorescence was studied in 33 normal subjects, 97 eyes with drusen only, and 111 eyes with visual loss caused by age-related macular disease.

RESULTS

Fundus autofluorescence intensity in normal subjects was highest at the posterior pole and dipped at the fovea. Autofluorescence increased with age at the posterior pole. Fundus in eyes with age-related maculopathy showed localized high autofluorescence that did not correspond with drusen. Linear pigmentation at the level of the retinal pigment epithelium (RPE), whether detached or flat, fluoresced brightly, whereas plaques of melanin did not. Areas of low and high levels of autofluorescence were seen in lesions containing choroidal new vessels. In areas of geographic atrophy, autofluorescence was low.

CONCLUSIONS

The spatial distribution of background fundus autofluorescence and the correlation of autofluorescence with age in normal subjects imply that autofluorescence is derived from lipofuscin at the level of the RPE. Focal accumulation of autofluorescent material occurs at the level of the RPE in patients with drusen, but the drusen do not show marked increases in autofluorescence. It is likely that melanolipofuscin accounts for the high levels of autofluorescence, corresponding to linear pigmentation at the level of the RPE. Low-intensity autofluorescence occurs in the presence of retinal photoreceptor loss, and variable levels over disciform lesions probably relate to variations in metabolic activity of the RPE.