Progressive peripheral cone dysfunction

Case of unilateral peripheral cone dysfunction

Purpose

Peripheral cone dystrophy is a subgroup of cone dystrophy, and only 4 cases have been reported. We present a patient with unilateral peripheral cone dysfunction and report the functional changes determined by electrophysiological tests and ultrastructural changes determined by spectral domain optical coherence tomography (SD-OCT).

Case

A 34-year-old woman complained of blurred vision in both eyes. Our examination showed that her visual acuity was 0.05 OD and 0.2 OS. A relative afferent pupillary defect was present in her right eye. The results of slit-lamp examination, ophthalmoscopy, and fluorescein angiography were normal except for pallor of the right optic disc. SD-OCT showed a diffuse thinning of the retina in the posterior pole of the right eye. A severe constriction of the visual fields was found in both eyes but more in the right eye. The photopic full-field electroretinograms (ERGs) were reduced in the right eye but normal in the left eye. The multifocal ERGs were severely reduced throughout the visual field except in the central area of the right eye. The multifocal ERGs from the left eye were normal. The pattern visual evoked responses were within the normal range in both eyes. She had a 5-year history of sniffing paint thinner.

Results

Although the visual dysfunction was initially suspected to be due to psychological problems from the results of subjective tests, objective tests indicated a peripheral cone dysfunction in the right eye. The pathophysiological mechanism and the relationship with thinner sniffing were not determined.

Conclusions

Our findings indicate that peripheral cone dysfunction can occur unilaterally. Electrophysiology and SD-OCT are valuable tests to perform to determine the pathogenesis of unusual ocular findings objectively.

Cone cGMP-gated channel mutations and clinical findings in patients with achromatopsia, macular degeneration, and other hereditary cone diseases

Unrelated patients with achromatopsia, macular degeneration with onset under age 50 years, cone degeneration or dysfunction, cone-rod degeneration, or macular malfunction were screened for mutations in the three genes known to be associated with achromatopsia: the GNAT2 gene encoding the alpha subunit of cone transducin and the CNGA3 and CNGB3 genes encoding the alpha and beta subunits of the cone cGMP-gated cation channel. We found no examples of patients with GNAT2 mutations. Out of 36 achromats, 12 (33%) had mutations in CNGA3 (13 different mutations including five novel mutations) and 12 (33%) had mutations in CNGB3 (six different mutations including four novel mutations). All achromats with CNG mutations had residual, presumably cone function as determined by computer-averaged 30-Hz electroretinograms (ERGs). There was considerable variability in acuity and color vision, with most patients having acuities of 20/200-20/400 and complete absence of color perception, and others having acuities of 20/25-20/40 and some color vision. Two pseudodominant achromatopsia cases were uncovered, both with CNGA3 mutations, including one family in which some compound heterozygotes with achromatopsia mutations were clinically unaffected. We found two novel CNGB3 changes in three patients with juvenile macular degeneration, a phenotype not previously associated with mutations in the cone channel subunits. These patients had subnormal acuity (20/30-20/60), normal to subnormal color vision, and normal to subnormal full-field cone ERG amplitudes. Our results indicate that some patients with channel protein mutations retain residual foveal cone function. Based on our findings, CNGB3 should be considered as a candidate gene to be evaluated in patients with forms of cone dysfunction, including macular degeneration.

Health policy and eye care services in Jamaica

PURPOSE

To test the hypothesis that access to and amount of eye care services in Jamaica are inadequate and that this is related to insufficient eye care personnel and legal limitations on optometric practice in Jamaica.

METHODS

An eye care provider survey, a consumer survey, and a literature search were used for data collection. The consumer sample consisted of 500 subjects (aged 16 to 84 years or older) recruited from a stratified random sample of food markets in Jamaica. The provider sample consisted of 10 ophthalmologists and 10 optometrists, randomly selected from licensing rosters. Adequacy of amount of eye care services was measured by comparing the frequency of eye examinations in Jamaica with professional practice guidelines. Access was measured by the eye provider to population ratio compared with calculated need for adequate care.

RESULTS

Only 38.6% of the study population had received an eye examination within 3 years and only 23.4% reported having eye examinations at least once every 3 years. Over 43% had never received an eye examination. The total eye care provider/population ratio was only 2.04/100,000 and only 1.32/100,000 when optometrists are excluded.

CONCLUSION

Access to and amount of eye care services are severely inadequate in Jamaica. Outdated optometric laws governing the activities of eye care professionals compounds the problem.

Clinical study of a large family with autosomal dominant progressive cone degeneration

PURPOSE

Autosomal dominant cone degeneration is an uncommon disorder characterized by progressive photophobia, hemeralopia, decreased central vision, and dyschromatopsia. To better understand the variable expressivity of autosomal dominant cone degeneration, we studied a single, large family.

METHODS

We performed comprehensive ophthalmic examinations, full-field electroretinography, foveal electroretinography, and color vision studies on 73 family members.

RESULTS

Of the 73 family members, 34 were affected. Symptoms generally began in the first decade of life and slowly progressed into midlife. Ophthalmoscopic findings consisted primarily of macular granularity or central macular atrophy. The photopic full-field electroretinogram was important in establishing the diagnosis, although the results of the electroretinographic measurements varied across individuals. Either the foveal electroretinogram amplitudes were abnormally low or the foveal/parafoveal ratio was abnormal in all affected subjects.

CONCLUSIONS

No single test or finding was completely sensitive or specific for accurate diagnosis of autosomal dominant cone degeneration. Especially in the more mildly affected subjects, a constellation of symptoms, findings, and test results were used to diagnose autosomal dominant cone degeneration accurately.

Mapping of autosomal dominant cone degeneration to chromosome 17p

PURPOSE

We studied a single, large family with autosomal dominant cone degeneration in order to map the disease-causing gene.

METHODS

Seventy-three individuals in this family were examined, and 34 were found to be affected. Blood samples from 34 affected and unaffected family members were obtained for DNA analysis and linkage mapping. Fifty-three genetic markers were analyzed in this family by using short tandem repeat markers. These markers were primarily in candidate genomic regions.

RESULTS

Marker D17S796 generated a significantly positive LOD score of 4.21 (theta = .04; 10,000:1 odds in favor of linkage). Marker D17S513 gave a significant LOD score of 3.1 (theta = .096; 1,000:1 odds in favor of linkage). Other markers in the region generated suggestive findings, such as D17S786, with a LOD score of 2.7, and D17S945, with a LOD score of 2.41.

CONCLUSIONS

Our results indicate that a genetic defect that causes autosomal dominant cone degeneration is located on chromosome 17p in the region of recoverin. Recoverin, a retinal expressed gene, is an appealing candidate for this disease.

Optic disc pallor: a false localizing sign

A 20-year-old pregnant woman was referred with bilateral mild visual acuity loss and optic disc pallor. Because of profound color vision deficits out of proportion to her acuity loss, an abnormality of the cone photoreceptors was suspected. An electroretinogram confirmed the diagnosis of a cone dystrophy and precluded further costly and invasive testing. Cone dystrophy should be considered in the differential diagnosis of any patient with bilateral, nonrefractive visual loss, especially if color vision is disproportionately affected, even with a normal retinal appearance and no significant family history.

Amblyopia

Images

Progressive cone-rod dystrophy and high myopia in a Finnish family

Progressive cone-rod dystrophy was diagnosed in a 35-year-old man (the proband). In the family study, 29 of the relatives were examined. The brother of the proband was also found to have cone-rod dystrophy. In the family of the mother of the proband, there were four men who had high myopia possibly connected with cone-rod dystrophy. The other relatives had no signs of cone-rod dystrophy or high myopia. The relatives not examined were reported healthy with no eye trouble. The disorder could be autosomal recessive hereditary if only the confirmed cone-rod dystrophy of the proband and his brother is taken in consideration. However, no relationships between the families of the mother and father of the proband could be found going back to the year 1830. Therefore, the autosomal recessive inheritance was not established. The most probable mode of inheritance would be X-chromosomal recessive if high myopia and cone-rod dystrophy are thought to be parts of the same syndrome.