A Prism of a Different Color 
Editor’s note: In June’s “Focus on Refraction” column, authors Marc B. Taub, OD, MS, and Paul Harris, OD, reviewed the case of an 18-year-old experiencing blurry vision and intermittent diplopia. They recommended a reevaluation of the prescription and vision therapy. You can read this case here.

One question that I have about this very thorough evaluation of this patient: There is no mention of any keratometry readings. Did you take keratometry readings on this patient? Is the little amount of cylinder present equal to “stress cylinder” from accommodative dysfunction that also might be contributing to his visual problems?

As you are probably aware, at 18 years old this patient is susceptible to induced stress cylinder that should not be corrected if it does not correspond to his corneal readings.

—Steven Mordukowitz, OD, FAAO, Bronx, NY

Drs. Taub and Harris respond:
Thank you so much for taking the time to write. We actually did not obtain the keratometry readings in this case, but they certainly would have been helpful for the precise reason you pointed out. In this case, we did subjectively assess the vision with and without the cylinder since and the patient reported clearer, more comfortable vision.  

Since he was older and able to communicate the improvement effectively, we made the conscious decision to leave in the cylinder we found. As we reevaluate the patient once therapy has been completed, we do expect the refraction to change, and most likely, the cylinder will not be included in the next prescription.  

Sixth Nerve Palsy Headaches
Editor’s note: In July’s “Neuro Clinic” column, authors Michael Trottini, OD, and Michael DelGiodice, OD, reviewed the case of a 92-year-old male experiencing sixth nerve palsy. You can read this case here.

As both a professor emeritus and a clinician, I was troubled by the article “Sixth Nerve Palsy Prompts a Surprising Diagnosis.” First, it should not have been a surprise! (I presume by the notation that measurements were taken at distance, since 2Δ ET by convention in primary gaze means a 2Δ alternating esotropia at distance). 

Second, it is unusual for the patient to have a constant 2Δ alternating esotropia at distance. A left sixth nerve palsy usually presents with a 20Δ left esotropia (LET) (if the measurements were at near, then it should have been noted as LET. The prime denotes near testing). In my experience, sudden onset sixth nerve palsies almost always present as 20Δ esotrope at distance (plus or minus the original distance phoria) with a small esophoria at near (variation in the angle is dependent upon the original phoria). If the initial deviation is much less than 20Δ, then the patient must be watched since the disease might still be progressing. As a result, an incomplete sixth nerve palsy should be seen within a week and re-measured.

Third, the authors provided no relief for a patient presenting with diplopia. Sixth nerve palsies are best handled by applying a 20Δ Fresnel prism on the superior portion of the affected eye’s lens (i.e., cut the prism and apply). This will eliminate the diplopia and can be easily removed upon resolution. Patching, which is often taught as a treatment, is a horrible way to eliminate diplopia, since it makes the patient non-functional (leading to a loss of depth perception and binocular field of view). 

Leaving the patient diplopic is unacceptable. The last method, Botox, is unpredictable, but acceptable if the patient does not want a patch or Fresnel prism.

Fourth, and most important, these patients with a presumed isolated sixth nerve palsy should be immediately worked up. The following should be performed: visual fields, physical examination by PCP, complete blood count, blood sugar, HbA1C, ESR, C-reactive protein, Lyme titer ANA (depending on where you live), VDRL and rheumatoid factor test. 

Isolated sixth nerve palsy rarely has a positive MRI, so that should be done if it does not resolve in six months. The problem is, if you don’t order an MRI, the PCP probably will, right or wrong, which puts the referring optometrist in the position to justify to the patient why you didn’t order the test. It is best to call the primary care physician and discuss whether or not to order an MRI. Delaying the diagnosis and treatment of a patient with a high ESR and GCA can result in rapid permanent loss of monocular or binocular vision. Happily, your patient did not develop ischemic optic neuropathy. The tests needed to be ordered right away, not one month later!

In summary, rapid workup of these patients, including ESR, is essential to prevent visual loss. Diplopia in the elderly may be a result of GCA and requires an immediate evaluation. Application of Fresnel prism can keep these patients comfortable.

—Jeffrey Cooper, MS, OD, FAAO, New York, NY

Drs. Trottini and DelGiodice respond:
The diagnosis was a surprise, as GCA causes less than 4% of sixth nerve palsies.¹ We are aware of the connection, but this case was atypical because our patient didn’t develop GCA symptoms until almost three months later (typically these patients have GCA symptoms upon presentation). Not to mention, our editors choose catchy titles to bring attention to the article. 

We have seen a significant number of sixth nerve palsies both less than and greater than 20Δ, so we don’t agree that sixth nerve palsies almost always present with a 20Δ esotropia. One study described clinical features of sixth nerve palsies, stating that out of 63 patients, the deviation ranged from 13.3pd to 34.3pd.² We also question the comment that “sixth nerve palsies are best handled by applying a 20Δ Fresnel prism” to alleviate diplopia. To give all sixth nerve palsies a 20Δ Fresnel is inappropriate; the prism should be determined on a case-by-case basis. To use our patient as an example, who only had a 2Δ esotropia in primary gaze, a 20Δ Fresnel would have significantly overcompensated and he still would have been diplopic.  

Concerning the reccommendation that “patients with a presumed isolated sixth nerve palsy should be immediately worked up,” this argument has been debated and well documented among optometrists, ophthalmologists and neuro-ophthalmologists; however, no general consensus or finite guidelines exist regarding initial testing. Depending on which study you read, the incidence of non-microvascular isolated nerve palsies ranges from 1% to 16%.^1,3,4 There was a great point-counterpoint article between Nicholas Volpe, MD, and Andrew Lee, MD, in a recent issue of the Journal of Neuro-Ophthalmology in which they debated initial neuro-imaging for isolated third, fourth and sixth nerve palsies.⁵ Even two elite members of the neuro-ophthalmologic profession were not able to come to a consensus. So, to make the statement that patients with a presumed isolated sixth nerve palsy should be immediately worked up is more of an opinion rather than a fact. 

It is our belief that the decision to run an MRI in these cases should be at the discretion of the eye care provider. If concerned about the PCP ordering it unnecessarily, share with that doctor your recommendation of initial observation. As the commenter points out, MRI shows a low yield and thus only recommends imaging after no resolution in six months; however, he recommends getting immediate laboratory studies with an even lower yield such as the RF, ANA and VDRL. A few case reports of sixth nerve palsies as the initial manifestation of lupus exist; however, the patients were 35- and 48-year-old females, which fits the epidemiologic profile of lupus far greater than that of a 92-year-old male.^6,7 Syphilis in a 92-year-old is extremely unlikely; also, we aren’t aware of any case reports or connections between rheumatoid arthritis and sixth nerve palsies.  

As for the ESR and CRP, the general recommendation is to obtain these tests in older individuals with suspected GCA. Otherwise, again, the yield is quite low. We did comment in our article that, because the incidence of GCA increases exponentially after age 80, and because of our experience managing this patient, we felt immediate testing of the ESR and CRP in this subset of patients may be helpful regardless of symptoms. Even with this recommendation, it is unknown whether our patient’s ESR and CRP would have been elevated initially or not until the disease progressed when he started developing constitutional symptoms.  

Lastly, we did communicate with this patient’s internist to re-evaluate and continue managing his vascular issues. We also prescribed a temporary Fresnel prism to alleviate our patient’s diplopia. Unfortunately, due to space constraints with a brief column we were not able to elaborate on every detail of the case. 

1. Tamhankar M, Biousse V, Ying G, et al. Isolated Third, Fourth and Sixth Cranial Nerve Palsies From Presumed Microvascular Versus Other Causes: A Prospective Study. Ophthalmology  2013;120:2264-9.
2. Park U, Kim S, Hwang J, Yu Y. Clinical features and natural history of acquired third, fourth, and sixth cranial nerve palsy. Eye.2008;22:691–6.
3. Chou K, Galetta S, Liu G, et al. Acute ocular motor mononeuropathies: prospective study of the roles of neuroimaging and clinical assessment. J Neurol Sci. 2004;219:35-9.
4. Murchison A, Gilbert M, Savino P. Neuroimaging and acute ocular motor mononeuropathies. A prospective study. Arch Ophthalmol. 2001;129:301-5.
5. Volpe, Nicholas J., Lee, Andrew G. Do Patients with Neurologically Isolated Ocular Motor Cranial Nerve Palsies Require Prompt Neuroimaging? J Neuro-Ophthalmol. 2014;34:301-5.
6.  Sedwick L, Burde R. Isolated sixth nerve palsy as initial manifestation of systemic lupus erythematosus. A case report. J Clin Neuroophthalmol 1983;3(2):109-10.
7.  Saleh Z, Menassa J, Abbas O, et al. Cranial nerve VI palsy as a rare initial presentation of systemic lupus erythematosus: case report and review of the literature. Lupus. 2010 Feb;19(2):201-5.