Ocular Albinism

TYPES OF OA

Two distinct forms of ocular albinism (OA) are recognized, both of which do not involve skin pigmentation.

OA Type 1(Nettleship-Falls Syndrome)

Nettleship-Falls ocular albinism, an X-linked recessive disorder, predominantly affects boys. Representing about 10% of all albinism cases, it’s the most common type of ocular albinism, with an estimated occurrence rate of between 1 in 50,000 to 150,000 live births.

The disorder is attributed to mutations in the GPR143 gene, which is responsible for coding an intracellular G-protein coupled receptor (GPCR). This receptor plays a crucial role in melanosome transport in pigment cells. Disruptions in this process lead to variations in the number and size of melanosomes. Individuals with OA1 typically exhibit larger melanosomes, known as macromelanosomes, detectable through skin biopsies.

The severity of OA1 symptoms often varies based on an individual’s ethnic background. Those from darker pigmented backgrounds tend to experience less severe effects compared to those from lighter pigmentation groups. Ocular albinism typically results in significant eye albinism with compromised vision. Diagnostic approaches for OA1 include molecular analysis of the OA1 gene (GPR143), family pedigree studies, and carrier mother examinations.

OA Type 2

Also referred to as Aland Island eye disease or Forsius-Eriksson type ocular albinism, OA2 is a less common X-linked disorder. It shares many clinical features with OA1, with additional symptoms like protan color vision defects (red & green color blindness) and impaired dark adaptation. Skin biopsy examinations show that OA2 is morphologically distinct from OA1, and female carriers of OA2 don’t show the characteristic fundus pattern found in OA1 carriers. The clinical manifestations of OA2 have some overlap with congenital stationary night blindness (CSNB2A).

PREVALENCE:

In North America, healthcare records do not specifically track the occurrence of albinism, but estimates suggest it ranges from 1 in 20,000 to 1 in 50,000 individuals. The actual prevalence of Nettleship-Falls albinism might be higher than 1 in 50,000, considering potential misdiagnoses. Albinism is usually identified in early childhood or infancy. Oculocutaneous albinism is equally prevalent in both genders, whereas ocular albinism predominantly affects males due to its X-linked inheritance pattern.

Albinism occurs across all ethnicities. Type II oculocutaneous albinism is more common among African American and African populations. Additionally, Hermansky-Pudlak syndrome has a notably higher prevalence in individuals of Puerto Rican descent. In African nations, the frequency of type II oculocutaneous albinism is considerably higher, varying from 1 in 2000 to 1 in 5000.

Understanding these statistics is crucial for better awareness and management of albinism across different populations and regions. This knowledge aids in providing appropriate health care and support services to those affected by albinism.

SIGNS AND SYMPTOMS

Features of Ocular Albinism

Eye Pigmentation: Individuals with albinism typically have light blue eyes due to minimal pigment in their iris, though the misconception of red or pink eyes is not commonly true in most children with albinism.

Iris Transillumination: In a typical eye, when light is shone into it, it reflects out, leading to “red eye” in photos. However, in albinism, light also passes through the iris, not just the pupil, a phenomenon known as iris transillumination. This is usually detectable only by an eye specialist.

Nystagmus: A common condition in children with albinism is nystagmus, where the eyes rapidly move or “shake” in various directions. This tends to lessen with age and often stabilizes by age seven. Contrary to some beliefs, nystagmus doesn’t cause a perception of a “moving world.”

Chiasmal Misrouting: Normally, the optic nerves cross partially at the optic chiasm, aiding proper vision and image transmission. In albinism, this crossing is uneven (e.g., 30% to one side, 70% to the other), known as chiasmal misrouting. While common in albinism, it is rare in those without the condition. A visual evoked potential (VEP) test can determine if this is present.

Light Sensitivity (Photophobia): Due to a lack of pigment to absorb light in the eyes, individuals with albinism often experience light sensitivity. While usually not painful, it can be uncomfortable. Wearing sunglasses or tinted contacts, and caps can help manage this sensitivity indoors and outdoors.

Additional Ocular Symptoms:

– Difficulty with depth perception.

– Eyes that do not align correctly.

– The presence of strabismus (crossed eyes) or amblyopia (“lazy eye”).

Understanding these characteristics can help in better management and accommodation for those with ocular albinism. Regular eye check-ups and appropriate visual aids are crucial for optimal vision care.

CAUSES

Ocular albinism (OA) is characterized by a deficiency in pigment production by the eye’s pigment cells, particularly in the iris and the retinal pigment epithelium. The exact mechanism by which this reduced pigment production affects visual acuity, causes nystagmus (involuntary rapid eye movement), and heightens sunlight sensitivity remains unclear. It’s not certain whether the lack of pigment is directly responsible, or if the issue lies within a different aspect of the eye’s developmental process and visual system formation.

Further research is necessary to fully understand the relationship between pigment production and these visual impairments in OA. This understanding could lead to more effective treatments and management strategies for individuals with ocular albinism.

INHERITANCE

Ocular Albinism (OA) primarily impacts boys as it’s an X-linked genetic condition. In affected boys, a mutation occurs in their sole GPR143 gene, which provides body development and function instructions. Girls may carry this gene mutation without showing signs of ocular albinism, though some might exhibit minor iris transillumination visible in eye examinations. It’s rare, but some girls may exhibit ocular albinism symptoms, which are typically less severe than those in boys.

On the other hand, Oculocutaneous Albinism (OCA) is typically inherited through an autosomal recessive pattern. This means both gene copies in an individual are affected. OCA affects both genders equally. Carriers of OCA, who can be male or female, usually have one functional and one non-functional gene copy and don’t show symptoms. Several genes can cause OCA, with the TYR gene and the OCA2 gene being the most prevalent.

These genetic differences underline the need for personalized genetic counseling and testing for accurate diagnosis and management of these conditions.

Differential Diagnoses

Syndromic forms of albinism differ from oculocutaneous albinism as they are linked to anomalies in cellular protein packaging and distribution, rather than a deficiency in melanin production.

Hermansky-Pudlak Syndrome (HPS): This condition includes ocular albinism as one of its components. HPS is a rare autosomal recessive disorder that also involves a predisposition to bleeding due to a lack of platelet storage, potential lung disease, and granulomatous colitis, which varies based on the specific subtype.

Albinoidism: This condition is an autosomal dominant mutation with incomplete penetrance, leading to reduced pigmentation. Individuals affected by albinoidism typically maintain normal vision and retinal development and do not experience nystagmus.

Waardenburg Syndrome (WS): WS, an autosomal dominant disorder, is recognized by irregular depigmentation patches on the hair and skin, resembling a piebald pattern. It also features heterochromia irides (an irregularity in iris pigmentation) and a wider nasal root.

Each of these conditions presents unique characteristics and symptoms, distinguishing them from traditional forms of albinism.

Chediak-Higashi Syndrome (CHS)

Blood smear showing giant azurophilic granules in neutrophils, characteristic of Chediak-Higashi Syndrome.In the last two decades, less than 500 cases of a specific rare autosomal recessive disorder have been reported, categorizing it as one of the three silvery hair syndromes.

Griscelli Syndrome (GS): GS is part of the silvery hair syndrome group and is an uncommon autosomal-recessive condition. It is characterized by skin and hair hypopigmentation (resulting in silver-colored hair), neurological issues, and may include immune system deficiencies or hematophagocytic syndrome

Elejalde Syndrome (ES): This condition, which should not be confused with the distinct acrocephalopolydactylous dysplasia also known as Elejalde syndrome, is another name for Neuroectodermal melanolysosomal disease.

These conditions, while rare, are significant in the study of genetic disorders, each presenting with unique clinical features and requiring specialized medical attention.

TREATMENT

Eye Care for Albinism-Affected Children

It’s important for children with albinism to have their eyes examined annually. Prior to starting kindergarten, check their visual acuity (VA) with an eye doctor. Children with a VA of 20/70 or lower might require vision assistance in school.

Children with albinism often sit close to screens or hold books near their face, which is typical and doesn’t harm their eyesight.

Aids and Tips for Enhancing Vision

Consider these devices and strategies to improve your child’s vision:

Glasses

– Prescription glasses can improve visual acuity, though they might not achieve 20/20 vision.

– Sunglasses can protect their eyes from intense light.

– Tinted lenses, like corning lenses or colored contacts, benefit those sensitive to light.

– Prism glasses can help manage correct strabismus.

Low-Tech Visual Aids

– Magnifiers, available in various types like dome, stand, or handheld, can enlarge text and images.

– Monocular telescopes aid in seeing distant objects and can be worn around the neck.

– Closed Circuit Television (CCTV) magnifies text and photos, adjusting brightness and contrast to reduce glare. Consider having one at home and in school.

– While white canes are not commonly used for navigation by those with albinism, they can signal visual impairment to others, especially drivers.

High-Tech Aids

For older students with extensive reading needs:

– Software like JAWS and ZOOMTEXT enlarges computer screen elements.

– Computerized dictation programs.

– Video cameras that magnify images and connect to laptops.

Vision Itinerant Teacher

Ensure your child has access to a vision itinerant teacher if they have low vision. This teacher will assist in adapting their learning environment, such as providing large print books and front-row seating in the classroom.

In places like Ontario, the Assistive Devices Program (ADP) may help fund vision aids for your child. A low-vision assessment, recommended by an eye doctor, can introduce various helpful devices.

Living with Ocular Albinism

For those with ocular albinism, a range of visual aids can be beneficial. This includes bifocal and prescription reading glasses, as well as contact lenses. Handheld magnifiers are another helpful tool. Positioning indoor lighting behind rather than in front can also significantly enhance visibility for individuals with this condition.

Interestingly, in certain states, individuals with ocular albinism who may qualify as legally blind are still eligible for a driver’s license. This is possible with the use of bioptic glasses, which are equipped with small telescopic devices.

Regular eye examinations, at least annually, are crucial for people with ocular albinism. An eye specialist can ensure they have the correct prescription for their glasses or contact lenses, optimizing their vision.

Children with ocular albinism might face challenges in educational settings due to difficulty seeing blackboards or screens. Engaging with the school to arrange for large-print materials, strategic seating, and classroom assistance can be immensely helpful. Eye doctors may also recommend tools like glasses with mini-telescopes and technological aids such as computerized dictation programs and video camera devices that bring images closer, enhancing the learning experience for these children.

PROGNOSIS

The outlook for vision among albinism patients tends to differ widely. In those diagnosed with type I oculocutaneous albinism, an enhancement in vision clarity is generally not observed. However, in other variants of albinism, there’s a possibility for improved visual acuity as pigmentation levels increase with age. It’s important to note that while some forms of albinism might see slight visual improvements over time, regular eye check-ups and appropriate visual aids are essential in managing the condition effectively.

QUESTIONS

What is the typical spectrum of visual sharpness observed in people with Ocular Albinism?
Individuals with Ocular Albinism (OA) typically have a visual acuity that is less than the standard 20/20. In young adults and adults with OA, the range of their best-corrected visual acuity can vary significantly, from as high as 20/30 to as low as 20/400, covering a broad spectrum within these limits.

What is the reason that corrective eyewear or contact lenses are ineffective in fully addressing visual issues in Ocular Albinism?

The ultimate visual quality in individuals is influenced by two primary factors. Firstly, the fovea, the central part of the retina responsible for detailed vision, is underdeveloped. This limitation hinders the retina’s ability to capture a clear image for transmission to the brain. Secondly, the altered pathways of image transmission and the imbalanced neural connections between each eye and the brain lead to imperfect image interpretation. As a result, even with correctly focused lenses, the retina (akin to a camera’s film) fails to capture a sharp image, and the brain (comparable to a computer) does not receive a precise visual signal.

Is there any examination that can reliably prognosticate visual acuity for infants with OA? 
The Visually Evoked Potential (VEP), also known as Visually Evoked Cortical Potential (VECP), is a diagnostic test similar to an EEG or brain wave examination. This test reveals how visual information is transmitted from each eye to the corresponding side of the brain when each eye is independently stimulated. However, in infants, accurate prediction of final visual acuity is challenging as their visual pathways are still developing, typically until the age of 7-9 years. Therefore, early VEP results in infants don’t definitively determine the ultimate level of visual clarity they will achieve.

Is OA a progressive or degenerative condition? 
Typically, children with ocular albinism experience an improvement in their visual sharpness as they grow older. This enhancement is partially attributed to the ongoing development of the brain’s nerve pathways. Additionally, as infants and children mature, they become more adept at visual tasks such as reading letters and identifying images on a screen. Importantly, ocular albinism is not considered a degenerative condition, and the majority of teenagers and young adults with this condition retain their vision for life. While complete blindness due to ocular albinism is rare, individuals with the condition may still meet the criteria for legal blindness.

What is the difference between ocular albinism (OA) and oculocutaneous albinism (OCA)? 
Individuals with Ocular Albinism (OA) and Oculocutaneous Albinism (OCA) often face similar vision challenges. However, there’s a notable difference in hair and skin pigmentation between the two conditions. While both OA and OCA generally result in less pigmentation than their non-affected family members, the degree and appearance of this pigmentation can vary considerably between the two types of albinism.

Do some kids with OCA have normal hair and skin pigment? 
Indeed, individuals with a specific type of Oculocutaneous Albinism, mainly type OCA1B, often display hair and skin pigmentation that is almost on par with typical levels, similar to those observed in individuals with Ocular Albinism.