Download Case Report Ocular Albinism

Aaney Andrud
4th Year
University of Missouri St. Louis
Hoya Vision Care Grant and Scholarship Program
A Troubled Progressive Lens Wearer
Case Report
Ocular Albinism
1
Ocular Albinism
Introduction
Ocular albinism is a condition where the skin and hair may have normal to near
normal pigmentation, but the eyes lack melanin. It is a genetic condition with four
subclasses. Each of the subclasses varies based on inheritance pattern, phenotypic
presentation, and ocular presentation. People affected by ocular albinism often have
reduced visual acuity, redu ced stereo acuity, strasbismus, nystagmus, photophobia, and
symptoms of glare.1
During the developmental period, a person with ocular albinism does not have
sufficient uveal pigmentation. This leads to poor maturation of the retinal pigment
epithelium (RPE). Thus, the retina does not contain the means for normal formation .
The macula is hypoplastic and leads to a pendular nystagmus and decreased visual
acuity.2
Persons with ocular albinism often have iris transillumination defects. This and
the lack of a sufficient RPE pigmentation are the cause for much of the glare and
photophobia that is experienced .
The strabismus is believed to be caused by the abnormal decussation of the optic
nerve. Twenty percent of what would normally be ipsilateral temporal fibers to decussate
at the ipsilateral lateral geniculate nucleus, instead decussate at the optic chiasm and
project to the contralateral lateral geniculate nucleus.1
2
Case Description
A fourteen year old African American female, A.K., presented for a low vision
evaluation. Her primary care examination revealed that she has ocular albinism. She has
normal skin and hair pigmentation. No one in her immediate family has any form of
albinism o ther than herself. The patient’s history states that one of her relatives is a
person whom has albinism. The pt. is not on any medications, nor does she have any
allergies. The patient’s chief complaint is that she cannot see the board in school. Upon
further discussion with the patient’s mother it is revealed that since the school’s last
record of a need for special visual requirements was dated in 2003, A.K. was to get a new
low vision evaluation in order to keep receiving the use of low vision aids for this lifelong condition. Thus, the patient’s teacher was denying the patient any special privileges
to help the patient meet her visual needs. The present school year had been in secession
for one month. Upon review of the patient’s activities in school it is determined that the
patient has been getting the information from another student. The other student had
been writing largely in her notebook so that A.K. could see them and then proceed to
write them largely into her own notebook. When the teacher became aware of this
activity it was put to a stop. A.K. has had a very difficult in time doing her school work.
A.K. had tried to use a sheet magnifier and a drug store magnifier in the past, but found
them of little value. The board at the front of the room is a white -board and causes a lot
of problems with glare. She had reported sitting to the front left side of the class room.
The examination revealed that her unaided distant visual acuities were 20/400
OD, OS, OU. Pupils were equal, round, and reactive to light. The patient did not have an
afferent papillary defect. A.K. did not have global stereo acuity. Confrontations and
3
EOMs were full. Cover test revealed that the pt. was a 10 prism diopter constant right
exotrope. Pt. has a constan t pendular nystagmus with a null point when looking forward
and central. Her refractive error was reconfirmed with a trial frame refraction and
retinoscopy and is as follows:
OD: +10.00-2.50x160
OS: +10.50-3.00x175
The anterior segment examination did not reveal any iris transillumination defects. The
posterior pole was blond and had visible choroidal vasculature 360 degrees. The optic
nerve heads exhibited mild pallor, oval in shape, a temporal tilt, and a cup to disc ratio of
0.60/0.60 for both eyes.
The patient’s near VA was 20/400 in both eyes. Using relative distance
magnification at 20cm the pt. could read 20/200 print. It was found that A.K. could read
20/40 print with the use of a 4x fixed -focus magnifier with an LED light. A monocular
hand-held telescope was found to help with distance vision
it to OS 20/60.
The hand-held telescope had a variable focus and a neck strap to be used in variable
settings. An inquiry was made with the school if it could be arranged for A.K. the use of
a closed circuit TV.
A.K. was fit into a pair of glasses. The Hoya Phoenix lens was chosen for the
patient because it offers A.K. the maximum protection to her eyes in regards to the most
extreme impact resistance that can be offered with today’s technology. The lens has 60x
the impact resistance of a standard plastic lens. The lens is a trivex material with an
index of refraction of 1.53. The trivex lens may be a little thicker than a polycarb onate
lens with an index of refraction of 1.58, but trivex has the lowest specific gravity (1.11
4
g/cm3 ) then any other lens currently available. Taking that into consideration the lens
will be light and thin with consideration to the patient’s high refractive error. It is also
free of optical stress and d istortion. The optical quality of a polycarbonate lens, or lack
there of (Abbe value of 29), makes the choice of the Hoya Phoenix literally clear (Abbe
value of 45). It is especially important to take into consideration that this patient is at
greater risk for damage caused by ultraviolet light. The Hoya Phoenix lens gives the
maximum protection by blocking 100% of all UV -A and UV- B rays. This patient needed
an Amber one tint to her lenses to help decrease her problems with glare. This factor also
made the choice of lens obvious that it had to be a trivex material. Polycarbonate does
not tint well, especially when compared to trivex.3
Discussion
There are three main types of albinism; Oculocutaneous, Cutaneous, and Ocular.
Oculocutaneous types of albinism exhibit a phenotypic total lack of pigment.
These people will have blue transilluminated irises, white hair, and skin color ranging
from pale to silky white when compared with others of the same ethnic or racial
background. Vision problems include moderate to severe nystagmus, moderate to high
astigmatism, photophobia, strabismus, and marked low v ion. There are 10-20 types of
oculocutaneous albinism. The two main types are tyrosinase negative and tyrosinase
positive. A person is classified as tyrosinase negative when their hair bulbs indicate that
there is no tyrosinase enzyme available to make melanin. Visual acuity is usually about
20/200, but can vary from 20/25 to 20/400. A person whom is tyrosinase positive has the
tyrosinase enzyme but it is unable to capture the synthesized melanin into the
5
melanosome to make melanin pigment. Less severe visual side effects are observed in
the tyrosinease positive patients.2
Cutaneous albinism shows the classic signs of oculocutaneous albinism at birth
but, they are able to produce a small amount of tyrsoinase enzyme to make melanin.
These people are able to develop a slight tan with sun exposure and may not even realize
that they have this condition. Their skin’s pigmentation continues to darken from birth to
age six. Visual acuity can range from 20/30 to 20/400.
Ocular albinism is divided into 4 subclasses. All of the subclasses are tyrosinase
positive. Class 1 is X-linked, therefore affects only males. Class 2 is also X-linked, but
is associated with loss of high -frequency hearing between puberty and age 40.
It is most likely that this patient, A.K., has Class 3 ocular albinism. Class three is
a recessive trait. Both male and females are affected equally. In this situation both
parents must be a carrier of the gene. The gene has a 25% chance of being
phenotypically expressed. This subclass will have normal hair and skin color, but will
have visual acuity of 20/100 to 20/400.
People with class 4 ocular albinism have an excessive amount of freckles on the
skin and have hearing loss. This type of inheritance is autosomal dominant.2
6
References:
1) Sowka JW, Gurwood AS, Kabat AG, Handbook of Ocular Disease Management.
Review of Optometry March 15, 2007; Sect 58A
2) Weber JM, “Ocular Albinism - Optometric Management of Genetic Eye Disorders.”
Marchon Continuing Education Program; 98
3) Benjamin K., “Trivex vs. Polycarbonate: A Material Comparison.” Laramy -K
Optical; 2007
7