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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