Vision Rehabilitation in Cone-Rod Dystrophies

Abstract: A 19-year-old male with Rod-Cone Dystrophy (RCD) presents for low vision rehabilitation (LVR). Findings include decreased VA, dark-adapted ERG, light-adapted ERG, mfERG, HVF, and abnormalities on FAF. LVR results in functional success.

I. Case History

• 19 year old Caucasian male • Chief Complaint: Referred to the San Antonio Lighthouse for the Blind by Houston eye Institute a low vision evaluation and continued care. • Medical History: The patient had a normal birth history. At the age of 14 he was diagnosed with RCD through and electrodiagnostic testing at Houston Eye Institute. By age 18 he had discontinued driving due to his . • Ocular History: He reported a significant decrease in vision over the last 6 months. • Medications: None • Family Medical/Ocular History: No known Medical/Ocular history • Social History: He is currently enrolled in college and would like to keep up with his classes. • Low Vision Devices: No previous devices • Goals: • Near: To efficiently read school books and notes in order to continue pursuing a college degree • Distance: To safely drive again, read off the school board, and see street signs. • Functional goals: Decrease glare and light sensitivity in all daily tasks • Mobility goals: Increase walking confidence in new areas

II. Pertinent findings:

• Habitual spectacle prescription: • OD: -0.50-2.00x010 • OS: -1.00-1.75x180 • Aided Visual Acuities: • OD: 10/80 (20/160 Snellen Equivalent) with 3:00 PRL, single letter near 0.30/2.5M • OS: 10/180 (20/360 Snellen Equivalent) with 9:00 PRL, single letter near 0.3/2M • Pelli-Robson Contrast Sensitivity chart: OD: Log 0.75 Severe, OS: Log 0.6 Severe • Trial frame Refraction: • OD: -0.50-1.50x025 10/40 • OS: -1.00-1.25x155 10/60 • Internals: OU: Peripheral areas of pigment disruption more prominent nasally OU, (-) FLR OU, significant disruption of macular pigment OU, C/D: 0.35/0.35 OU • Macular OCT: Thinning two standard deviations below normal OU. Central thickness subfield OD: 174µm, OS: 154µm • Fundus Autofluorescence: Foveal hyperpigmentation, ring of perifoveal hypopigmentation, ring of slight hypopigmentation outside of arcades. • Humphery Visual Field 120pt: Questionable reliability due to high false negatives OU. OD: 15/17 False negatives, OS: 17/18 False negatives. Significantly reduced peripheral and central visual field. • Scotopic Electroretinogram (ERG): Reduced a-wave and b-wave amplitudes OU. • Photopic ERG: Reduced a-wave and b-wave amplitudes OU. • Multifocal ERG (mfERG): Cone function responded two standard deviations below normal OU.

III. Differential Diagnosis:

• Primary: Cone-Rod Dystrophy (CRD) • Differential diagnosis: RCD with early macular involvement • Neuronal Ceroid Lipofuscinosis • Stargardt’s • Leber’s Hereditary Optic Atrophy • Bilateral maculopathy in adolescents

IV. Diagnosis and discussion:

• Diagnosis: Reduced central vision along with decreased peripheral function on electrodiagnostic testing secondary to CRD. • CDR is a phototransduction cascade disorder that results in abnormal cone function, followed by abnormal rod function.1 Symptoms can occur between birth and middle age depending on the variant of the genotype and its expression. CRD is illustrated by a variety of different central macular pigmentations upon fundoscopic examination and thus classified as a Pigmentary Retinopathy. In contrast to Rod-Cone Dystrophies like , CRD results from initial loss of cone photoreceptor function followed by rod photoreceptor function. • The initially noticed symptom of decreased central causes patients to develop a preferred retinal locus. In this early stage and a range of dyschromotopsia typically develop. Funduscopically, macular pigmentation develops with associated retinal atrophy, retinal vessels attenuate, and the optic nerve head develops temporal pallor.2 In the later stages of CRD as peripheral vision decreases as the patient’s nyctalopia becomes more apparent. Patients in the late stages progress to legal blindness due to acuity worse than 20/200. Although CRDs visual impairments occur earlier than RCDs the end stage of each disease is fairly similar visual impairments.2 • Prevalence of CRD in the United States is 1 per 40,000 and therefore ten times less common than retinitis pigmentosa4. It can be acquired through autosomal dominant5, autosomal recessive6, sporadic2, metabolic dysfunctions7 or idiopathic inheritance. CRDs like RCDs can also be part of syndromes such as Alström syndrome8 and polyglutamylase gene TTLL5.9

V. Treatment and Management:

Currently there is no cure for Cone-Rod Dystrophy. Therefore, treatment is aimed at improving quality of life with LVR and managing the psychological sequela associated with the disease. To meet the patient’s current demand target print size of 0.5M continuous text at threshold was selected to build in some reserve for fluent reading at a 1M text size. Based on his near acuities a Mattingly 6D/2.5x Illuminated Hand Held Magnifier was evaluated and allowed him to read 0.35/1M continuous text threshold; however, he rejected the use of the magnifier, as it was not adequate for his purposes when compared to the electronic forms of magnification. An Eschenbach SmartLux Hand Held Video Magnifier was also evaluated and allows him to read 0.3/0.2M threshold continuous text with a transverse magnification of 4.5, relating to an effective power of 15 diopters. The patient responded positively, accepted, and was pleased with the Eschenbach SmartLux Hand Held Video Magnifier. Lastly a Walters 2.8x telescope was evaluated and found to enhance acuity to 10/30-2. The patient understood why the telescope could be useful in the future, but rejected the device at this time due to lack of goal interest now that he was informed that he would not be able to legally drive due to peripheral vision loss. Upon evaluation of absorptive filters the patient was found to benefit from NOIR 50 yellow for indoor use and NOIR 40 amber16% solar shield for outdoor use. The patient responded positively to the training and device dispense of the Eschenbach SmartLux and felt that this device would suffice his needs at this time. He understands that with the progression of this disease and was educated that white cane orientation and mobility training will be beneficial to him. Fluctuations in visual acuity were attributed to a non-trained preferred retinal locus (PRL). to train a PRL can help to isolate an area of preserved vision, optimize the remaining vision, enhance device success and increase acceptance of devices due to increased consistency.

• Research in the area of CRD is directed supplementation and gene replacement therapy, but has been unsuccessful at slowing or halting progression. • The following recommendations were made: 1. Spectacle Rx released with NOIR 50 yellow for indoor use and NOIR 40 amber16% solar shield for outdoor use 2. Dispense Eschenbach SmartLux with training at dispense with to ensure maximum performance with electronic hand held video magnifier. 3. Referral for orientation and mobility, white cane training 4. Referral for genetic counseling 5. Educate patient and family on school resources, vocational counseling, and future employment assistance through the Department of Assistive and Rehabilitative services (DARS) Division of Blind Services (DBS) 6. Educate patient and family on progression of disease 7. Return annually to address low vision goals or sooner if goals arise

VI. Conclusion:

Cone-Rod Dystrophy is a rare genetically inherited condition with no cure at this time. Because vision loss is typically the first sign, Cone-Rod Dystrophy is often first suspected during an eye exam. The role of optometrists is to provide patients with the tools needed to function at the highest level and fulfill their visual potential. As low vision specialists the prognosis of the disease helps us to understand that future devices will be helpful. Forward telescopes are beneficial in the early stages of CRD and as the disease progresses; the reverse telescope’s assistance increases. Rapid onset of diseases such as CRD can leave the patient in a state of denial or bargaining impeding acceptance of devices. It is the low vision specialist’s responsibility to educate the patient in the different uses of devices, refer patients to counseling, and be patient for when the patient is ready to accept a device.

Bibliography:

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