Dark-adaptation functions in molecularly confirmed achromatopsia and the implications for assessment in retinal therapy trials

PURPOSE

To describe the dark-adaptation (DA) functions in subjects with molecularly proven achromatopsia (ACHM) using refined testing conditions with a view to guiding assessment in forthcoming gene therapy trials.

METHODS

The DA functions of nine subjects with ACHM were measured and compared with those of normal observers. The size and retinal location of the stimuli used to measure DA sensitivities were varied in four distinct testing condition sets, and the effect of altering these parameters assessed.

RESULTS

In three of the four testing condition sets, achromats had significantly higher mean final thresholds than normal observers, whereas in the fourth condition set they did not. A larger, more central stimulus revealed the greatest difference between the final DA thresholds of achromat and normal subjects, and also demonstrated the slowest rate of recovery among the achromat group.

CONCLUSIONS

In this, the largest study of DA functions in molecularly proven ACHM to date, we have identified optimal testing conditions that accentuate the relative difference between achromats and normal observers. These findings can help optimize DA testing in future trials, as well as help resolve the dichotomy in the literature regarding the normality or otherwise of DA functions in ACHM. Furthermore, the shorter testing time and less intense adaptation light used in these experiments may prove advantageous for more readily and reliably probing scotopic function in retinal disease, and be particularly valuable in the frequent post therapeutic assessments required in the context of the marked photophobia in ACHM.

Ametropia and Emmetropization in CNGB3 Achromatopsia

Purpose

Emmetropization is the process of adjusting ocular growth to the focal plane in order to achieve a clear image. Chromatic light may be involved as a cue to guide this process. Achromats are color blind and lack normal cone function; they are often described as being hyperopic, indicating a failure to emmetropize. We aim to describe the refraction and refractive development in a population of genetically characterized achromats.

Methods

Refractive error data were collected retrospectively from 28 medical records of CNGB3 c.1148delC homozygous achromats. The distribution of spherical equivalent refractive error (SER) and spherical error was analyzed in adults. The refractive development in children was analyzed by documenting astigmatic refractive error and calculating median SER in 1-year age groups and by analyzing the individual development when possible.

Results

The distribution of SER and spherical error resembled a Gaussian distribution, indicating that emmetropization was disturbed in achromats, but we found indication of some decrease in SER during the first years of childhood. The prevalence of refractive errors was high and broadly distributed. Astigmatic refractive errors were frequent but did not seem to increase with age.

Conclusions

Refractive development in achromats is more complicated than a complete failure to emmetropize. The spread of refractive errors is larger than previously documented. Results presented here support the theory that chromatic cues and cone photoreceptors may play a role in emmetropization in humans but that it is not essential.

ACBD5-related retinal dystrophy with leukodystrophy due to novel mutations in ACBD5 and with additional features including ovarian insufficiency

Acyl-CoA-binding domain-containing protein 5-related retinal dystrophy with leukodystrophy (ACBD5) is a peroxisomal disorder due to deficiency of ACBD5. Presenting features include retinal dystrophy, progressive leukodystrophy, and ataxia. Only seven cases of ACBD5-related retinal dystrophy have been reported in the literature to date, including one other case diagnosed in adulthood. Here we report a case with novel compound heterozygous ACBD5 mutations, presenting with the common features of rod monochromatism and progressive leukodystrophy with spasticity and ataxia. Additional novel clinical features included head and neck tremor and ovarian insufficiency. The patient's symptoms were present since infancy, but a diagnosis was only reached in adulthood when whole exome sequencing was performed. This case, which reports two novel mutations and additional clinical manifestations, contributes to the emerging phenotype of ACBD5-related retinal dystrophy with leukodystrophy, and delineation of the natural history and disease progression.