Clinical and mutational characteristics of oculocutaneous albinism type 7.

The purpose of this paper is to expand on the phenotype of oculocutaneous albinism type 7 (OCA7). We described three patients with OCA7: two from a consanguineous family of Kurdish origin and one patient of Dutch origin. We compared them with all patients described to date in the literature. All newly described patients had severely reduced visual acuity (VA), nystagmus, hypopigmentation of the fundus, severe foveal hypoplasia, and chiasmal misrouting. None had iris translucency. All patients had normal pigmentation of skin and hair. We found one novel mutation in the Dutch patient: c.565G > A; p.(Gly189Ser). We compared our patients to the 15 described in the literature to date. All 18 patients had substantially pigmented skin and hair, very poor VA (0.4-1.3 logMAR), nystagmus, (mild) ocular hypopigmentation, foveal hypoplasia, and misrouting. Although pigmentation levels were mildly affected in OCA7, patients had a severe ocular phenotype with VA at the poorer end of the albinism spectrum, severe foveal hypoplasia, and chiasmal misrouting. OCA7 patients had a phenotype restricted to the eyes, and similar to that of X-linked ocular albinism. We therefore propose to rename the disorder in ocular albinism type 2. Unfolding the role of LRMDA in OCA7, may bring us a step closer in identifying the responsible factors for the co-occurrence of foveal hypoplasia and misrouting.

Evident hypopigmentation without other ocular deficits in Dutch patients with oculocutaneous albinism type 4.

To describe the phenotype of Dutch patients with oculocutaneous albinism type 4 (OCA4), we collected data on pigmentation (skin, hair, and eyes), visual acuity (VA), nystagmus, foveal hypoplasia, chiasmal misrouting, and molecular analyses of nine Dutch OCA4 patients from the Bartiméus Diagnostic Center for complex visual disorders. All patients had severely reduced pigmentation of skin, hair, and eyes with iris transillumination over 360 degrees. Three unrelated OCA4 patients had normal VA, no nystagmus, no foveal hypoplasia, and no misrouting of the visual pathways. Six patients had poor visual acuity (0.6 to 1.0 logMAR), nystagmus, severe foveal hypoplasia and misrouting. We found two novel variants in the SLC45A2 gene, c.310C > T; (p.Pro104Ser), and c.1368 + 3_1368 + 9del; (p.?). OCA4 patients of this Dutch cohort all had hypopigmentation of skin, hair, and iris translucency. However, patients were either severely affected with regard to visual acuity, foveal hypoplasia, and misrouting, or visually not affected at all. We describe for the first time OCA4 patients with an evident lack of pigmentation, but normal visual acuity, normal foveal development and absence of misrouting. This implies that absence of melanin does not invariably lead to foveal hypoplasia and abnormal routing of the visual pathways.

[Functional vision disorder: timely examination pays off]. / Functionele visusklachten: tijdig onderzoek loont.

Patients with functional vision disorder (FVD) may present with poor visual acuity, visual field loss, or a combination of the two. This paper illustrates the utility of objective tests in diagnosing FVD. We use sweep visual evoked potentials and eye tracking as objective tests for visual acuity and visual field, respectively. These measurements should be made early in the diagnostic process because appropriate treatment becomes more difficult the longer the patient has been undergoing medical workups and referrals. Additionally, objective proof of better visual functions can be used as confirmation of the absence of a serious organic disorder. The results are used to convince patients and parents that vision is potentially much better than the patient experiences and to explain FVD. Consultation should preferably take place in a multidisciplinary setting with trained ophthalmologists and psychologists.

Retinally-induced aniseikonia.

PURPOSE: To show that retinally-induced aniseikonia may vary as a function of visual field angle (i.e., field-dependent aniseikonia), how this could be explained, and what implications this has for managing the aniseikonia. DESIGN: Observational case series. METHOD: Self-administration using software that can be assumed the predecessor of the Aniseikonia Inspector version 2. Aniseikonia was tested in the vertical nd horizontal direction. In each direction aniseikonia was tested for visual field angles of 0.5 to 8 degrees. PATIENTS: Three patients with different retinal conditions: an epiretinal membrane (ERM), a retinal detachment (RD), and a retinoschisis. RESULTS: All patients had field- dependent aniseikonia, with aniseikonia variations of up to 20% over the measured visual field. The aniseikonia for the ERM patient was similar in the vertical and horizontal direction, while this was not the case for the RD patient and the retinoschisis patient. The retinoschisis patient even had negative aniseikonia in one direction and positive aniseikonia in the other direction. CONCLUSIONS: When reporting the aniseikonia of patients with retinal conditions, one cannot speak of 'the' aniseikonia(i.e., a single value or a single value for each direction), because it is most likely field-dependent. It is also important to use a test that only measures static aniseikonia (direct comparison tests with long viewing times may be less suitable). Correction of field- dependent aniseikonia is relatively difficult, because an optical correction is field-independent. Nevertheless, optically correcting the aniseikonia for part of the visual filed often improves the vision comfort considerably. If necessary, an optical correction could be augmented with a unilateral partial transparency occlusion or a unilateral partial field occlusion for more vision comfort.

Retinal scanning display: light sources moving over the retina.

A retinal scanning display is a new kind of display that directly uses the retina as a projection screen. This differs from, for example, a TV which first creates an image on a screen outside the eye. Although a retinal scanning display needs no screen, the principle of creating an image is similar to that of a TV. Where the TV uses an electron beam to create (scan) a raster pattern on a screen, a retinal scanning display uses a beam of light to scan a raster pattern on the retina. The way to get from an equally illuminated raster pattern to an image is to modulate the intensity of the beam as it scans. Since the eye does not look at a physical screen, people often wonder what the image of a retinal scanning display will look like. Upon seeing the image, the general response is: 'It looks just like a normal display'. In fact it is a normal display, but one that has many advantages compared to other kind of displays, such as: possibility of high brightness, large color gamut, possibility of high-resolution and good image quality.

Resolution matching in a retinal scanning display.

In a retinal scanning display an image of a light source is scanned over the retina and at the same time modulated in intensity to form an image. To attain a retinal image most resembling the corresponding original image, the resolution of the modulating graphics board must be at least twice the maximum optical resolution possible. This paper describes how this relationship, which is based on the theorem of Shannon, is derived and what differences in contrast can be observed between the horizontal and the vertical scanning direction. It appears that for a relatively large field of view the resolution of the graphics board is inadequate, so that the maximum optical resolution will have to be decreased.

Safety norms for Maxwellian view laser scanning devices based on the ANSI standards.

Standards for safe use of lasers like those of the American National Standard Institute (ANSI) do not give specific guidelines regarding the safety norms for a Maxwellian view laser scanning device (for example, the scanning laser ophthalmoscope). In this note it is shown that a pulsed extended source ocular exposure system, which is described by the ANSI standards, can be used as a conservative model of such a laser scanning device. With some adjustments to this model, the Maxwellian character can be included and the maximum permissible corneal power also can be normalized independently of the field size.