Unilateral Retinitis Pigmentosa

Attention to the patient’s wishes is important, even in the most unusual cases.

By Danni Griffith

We are all floored when things that “never” happen, happen. Dr. Ken Eakland, one of my (DK) professors in optometry school, used to say, “It ain’t rare if it’s in your chair.” This statement rings so true. We get so caught up seeing the common things that we begin to ignore the uncommon until it presents. Sometimes the uncommon cases fly under our radar and may get missed. I love this case because it points out what is most important: treating the patient. It is so vital to work toward bringing the patient’s desires to the forefront of our treatments.

—Section Editors Mile Brujic, OD, FAAO, and David Kading, OD, FAAO

Retinitis pigmentosa (RP) comprises a group of hereditary, progressive retinal degenerations that result from abnormal production of photoreceptor proteins. RP is the most common retinal dystrophy, with a prevalence of 1 in 5,000 worldwide. It can occur through autosomal recessive, autosomal dominant, X-linked, isolated, and undetermined inheritance patterns.1 At least 29 loci are associated with various phenotypes of RP, and more are being discovered regularly.2

Figure 1. Fundus of the right eye (Optos) appears normal.

RP is bilateral and symmetric. Typical symptoms include nyctalopia, dark adaptation problems, photophobia, progressive constriction of visual fields, dyschromatopsia, photopsias, and slowly progressive decreased central vision. Signs include decreased visual acuity, constricted visual fields, decreased color vision, dark pigmentary clumps in the midperipheral retina, attenuated retinal vessels, cystoid macular edema, fine pigmented vitreous cells, and waxy optic disc pallor. There are also strong associations with posterior subcapsular cataracts, high myopia, astigmatism, keratoconus, and mild hearing loss. Prognosis is generally poor, and patients are usually legally blind by the fourth decade.

CASE HISTORY

A 57-year-old man presented for an annual eye examination with the chief complaint of blurring of distance and near vision. He reported being diagnosed with RP in his left eye at age 18 years, in 1976.

His glasses prescription in the right eye was +1.75 -5.00 × 012 with a balance lens in the left eye. Entering distance acuities with his glasses in place were 20/25-2 OD and 20/150 OS. Pupils and extraocular muscles were normal. Intraocular pressures with the iCare tonometer were 8 mm Hg OD and 6 mm Hg OS.

Figure 2. Fundus of the left eye demonstrates dark pigmentary clumps in the midperiphery and attenuated retinal vessels characteristic of RP.

Slit-lamp evaluation of the anterior segment revealed grade 2 nuclear sclerotic cataracts in each eye and grade 2 posterior supcapsular cataract OS. Posterior segment evaluation revealed a superonasal choroidal nevus OD and midperipheral pigmentary clumping and arterial attenuation OS (Figures 1 and 2).

Corneal topography was ordered based on irregular mires seen on autorefraction. Keratometry readings as computed from corneal topography were 50.40 D @ 101/45.10 @ 011 OD and 50.50 D @ 046/46.70 D @136 OS with inferior steepening characteristic of pellucid marginal degeneration OS greater than OD.

Final refraction was +1.00 -5.50 × 025 OD, yielding 20/25-2, and balance OS.

The patient was diagnosed with bilateral age-related nuclear cataracts, age-related posterior subcapsular polar cataract OS, pigmentary retinal degeneration OS, keratoconus OU, hypermetropia OD, astigmatism OD, and presbyopia OU. Based on reduced acuity and potentially visually significant cataracts, the patient was referred for evaluation for cataract removal.

DISCUSSION

Unilateral RP is an extremely rare condition, with fewer than 100 cases reported in the literature.3 It may appear in a primitive form (idiopathic) or secondary to inflammation (syphilis, toxoplasmosis, rubella, chickenpox, measles, cytomegalovirus) or to toxic (chloroquine, chlorpromazine), vascular (obstruction of the central retinal artery), traumatic, age-related, and neoplastic causes. It is diagnosed as unilateral RP only when the criteria of François and Verriest are fulfilled.2 The criteria for diagnosis of unilateral RP are:

1. The presence in the affected eye of functional changes and an ophthalmoscopic appearance typical of RP.

2. The absence in the other eye of symptoms of RP with the presence of a normal electroretinogram (ERG).

3. A sufficiently long period of observation (> 5 years) to rule out delayed onset in the unaffected eye.

4. Exclusion of an inflammatory cause in the affected eye.

The patient reported extensive testing early in life when the initial diagnosis of RP was made. He reported no known associated systemic inflammation or toxic, traumatic, age-related, or neoplastic causes. In order to correctly diagnose this patient with unilateral RP, further testing with ERG and visual fields would be recommended.

Figure 3. Corneal topography of the right eye demonstrates the beginning stages of inferior steepening.

If unilateral RP were the cause of the retinal findings, one would expect a decreased or absent response in scotopic and photopic ERG, as rods and then cones were damaged OS and normal ERG results OD. Visual fields of patients with RP show progressive visual field loss starting with a donut-shaped scotoma progressing to complete peripheral field loss with a preserved central island of vision. However, the patient was not interested in receiving further testing due to an overload of testing he underwent earlier in life.

This patient also noted challenges he has gone through in life as eye care providers have attempted to provide the best optical correction for his left eye. He mentioned difficulties with double vision and visual discomfort. He even remarked that it has become easier for him as the disease has progressed and there is less confusion between eyes.

Figure 4. Corneal topography of the left eye demonstrates pellucid marginal degeneration.

Contact lenses such as rigid gas permeable or scleral lenses could possibly improve the vision OS because the lenses would decrease the effect of the pellucid marginal degeneration, but they would be cautiously recommended in this case because the patient stated his preference for his functionally monocular status. Therefore, it was important to be cautious in proceeding with cataract surgery or other visual correction in this patient.

CONCLUSIONS

Unilateral RP is very rare. For nearly 40 years, this patient underwent many tests, and he tried option after option in search of the best visual acuity. He reported that his night vision has always been poor but has seemed a little worse recently. He also noted that binocular distance and near vision was not quite as good recently, which we attributed to the nuclear sclerotic cataract OD. Therefore, the patient was referred for cataract surgery OD to improve his symptoms.

The most important conclusions to be drawn from this case are to keep the needs and wishes of your patients in mind at all times, even in the most unusual of cases. n

1. Kaiser PK, Friedman NJ, Pineda R. Retinitis Pigmentosa (RP). In Kaiser PL, Friedman NJ, Pineda R. The Massachusetts Eye and Ear Infirmary Illustrated Manual of Ophthalmology. Philadelphia: Elsevier Saunders; 2014: 469-477.

2. Spadea L, Magni R, Rinaldi G, et al. Unilateral retinitis pigmentosa: clinical and electrophysiological report of four cases. Ophthalmologica. 1998;212(5):350-354.

3. Thakur A, Puri L. Unilateral retinitis pigmentosa. Clin Exp Optom. 2010;93(2):102-104.

Section Editor Mile Brujic, OD, FAAO
• Partner, Premier Vision Group, Bowling Green, Ohio
• (419) 352-2502; mile@optometricinsights.com

Section Editor David L. Kading, OD, FAAO
• Partner, Specialty Eye Group, Seattle, Washington
• (425) 821-8900; dave@optometricinsights.com

Danni Griffith
• Optometry intern, Pacific University College of Optometry-Class of 2016
thom3673@pacificu.edu