Patrick S. O'Connor

Air Travel and IntraocuIar Gas

The safety of air travel for persons with intraocular gas after ocular surgery has been in question since the mid 1970s, when the use of intraocular gases after vitrectomy became widespread. After vitrectomy, air-fluid exchange was performed on six Rhesus monkeys. During simulated air travel in an altitude chamber, intraocular pressure rose an average of 42 mmHg with intraocular air volumes as small as 0.25 cc. Hypotony was observed after return to ground level in all cases. Transient central retinal artery occlusion and pupillary block was observed. Patient safety and comfort is endangered during air travel with very small volumes of intraocular gas.

Episodic Unilateral Mydriasis and Migraine

Seven patients (all female, ranging in age from 5 to 53 years) had typical migraine and episodic unilateral mydriasis. These mydriatic episodes, usually occurring during the headache, lasted from 15 minutes to 24 hours and had occurred for three months to 35 years. Three patients had suffered from car sickness as children and there was a family history of migraine in six. Normal accommodation in five patients, normal responses to pilocarpine in two patients, and a return to normal or near-normal pupillary reaction in five patients with the cessation of headache made pharmacologic blockade unlikely. Although there are several possible neurogenic mechanisms, a parasympatholytic origin appears to be the most likely explanation for the mydriasis. Such episodes are generally benign.

Botolinum Toxin for the Treatment of Dysthyrolod Ocular Myopathy

Eight consecutive patients with acquired deviations due to dysthyroid ocular myopathy were injected with botulinum A toxin for relief of their diplopia. Seven patients were acute in the onset of symptoms and one was chronic. All showed improvement in motility and experienced a reduction if not total relief of their symptoms. Six patients required reinjection. Complications were limited to transient ptosis, transient involvement of adjacent muscles and transient but prolonged paralysis that eventually resolved. No systemic complications were noted. We conclude that chemodenervation with botulinum A toxin may have a role in the management of dysthyroid ocular myopathy not amenable to prism treatment and may act as an adjunct to or eliminate the need for surgical correction in some patients.

Acephalgic Migraine: Fifteen Years Experience

Sixty-one patients with acephalgic migraine have been seen and thoroughly evaluated at the USAF School of Aerospace Medicine over the past 15 years. Patient age ranged in years from 21 to 61, with the number of spells varying between 1 and 100 and lasting from 15 seconds to 3 hours. These phenomena were present for 2 weeks to 25 years. Ocular involvement was represented by scintillation, transient hemianopia, bilateral central scotomata, classic amaurosis fugax, diplopia, altitudinal field loss, tunnel vision; temporal crescent involvement, and several patients who developed a transient central scotoma in one eye with alterations in color perception. Other neurologic involvement occurred in 29%. Permanent neurologic deficit occurred in only one patient. Positive family history for migraine was present in only 24%. Headache is not a necessary feature of migraine attacks. One should consider migraine in any acute episodic neurologic disorder.

Retrobulbar Anesthesia Risk: Do Sharp Needles Really Perforate the Eye More Easily than Blunt Needles?

PURPOSE Conventional wisdom in ophthalmology is that the force required to perforate an eye during retrobulbar injection is noticeably greater with a specially designed blunt needle than with a standard hypodermic needle. A search of the literature showed no measurements of scleral perforation pressure with specific needle tips. The authors investigated this concept. METHODS A computerized search for eye perforations of the surgical records over a 5-year period at Wilford Hall United States Air Force Medical Center was conducted. A double-masked trial by experienced ophthalmologists, using preserved eye bank eyes and several commercially available needles, subjectively assessed the force required to perforate the globe. The authors designed and built a portable transducer system to objectively measure the perforation pressure of human globes with the needles. Measurements were done with preserved and unpreserved human cadaver eyes. RESULTS No globe penetrations or perforations were found in this consecutive series of over 4000 retrobulbar anesthesia procedures. A subjective difference between the hypodermic and blunt needles was detected. Objective measurements showed a significant difference between the hypodermic and blunt needles, and between types of blunt needles. The difference was present with both eye bank eyes and fresh cadaver eyes. CONCLUSIONS Blunt-tipped needles do require greater force to penetrate the eye. The noncutting edge, blunt-tipped needles have higher scleral perforation pressures than those with cutting edges.

Voluntary Alteration of Pattern Visual Evoked Responses

Pattern and flash visual evoked responses (VERs) were recorded from a large group of ophthalmologically normal subjects during two conditions: in one they were instructed to attend to the stimulus and in the other they were instructed to ignore the stimulus but maintain their gaze on the stimulus. Pattern VERs were recorded from 42 subjects. Fixation was constantly monitored during both attend and ignore conditions and no changes of fixation were noted at any time. The amplitude of the major positive wave of the pattern VERs produced by both 50- and 25-min checks was reduced significantly during the ignore condition. The implicit time of this positive wave did not differ significantly during the two conditions. The pattern VERs of eight subjects were extinguished and the VERs of another three subjects were unrecognizable during the ignore condition. Flash VERs produced by 10 flashes per second were recorded from 38 of the 42 subjects. There were no significant differences between the amplitudes recorded during the attend and ignore conditions.

Congruous and incongruous sectoral visual field defects with lesions of the lateral geniculate nucleus

Quantitative perimetric studies in two women, each 52 years of age, with involvement of the lateral geniculate nucleus (caused by a small arteriovenous malformation in one and by an astrocytoma in the other) disclosed a striking wedge-shaped horizontal sectoranopia that was perfectly congruous in one case and incongruous in the other. Selective interruption of the dual blood supply to the lateral geniculate nucleus (with the anterior choroidal artery supplying the anterior hilus, together with the anterior and lateral nucleus and the lateral choroidal artery supplying the remainder of the nucleus) may result in a congruous visual field defect with steeply sloping borders because such a lesion must respect the anatomic boundaries produced by this vascular supply. Partial infiltration or involvement of the lateral geniculate nucleus (where uncrossed retinal projections terminate in one group of laminae, while crossed retinal projections terminate in another) provides a logical explanation for the occurrence of incongruous visual field defects. This unusual horizontal wedge-shaped defect should suggest lateral geniculate nucleus involvement, especially in the absence of trauma.

Effect of cataract surgery and intraocular lenses on diabetic retinopathy

ABSTRACT We reviewed a series of 137 cataract extractions with intraoculai lenses (IOLs) in patients with diabetes mellitus between 1977 anc 1983. All patients were followed for an average of 36 months tc determine if they subsequently showed progression of diabetic retinopathy. Divided into groups according to the type of procedur (and IOL received, they were compared for age, sex, duration of diabetes, treatment required for the diabetes, intraoperative complications, and follow‐up period. Patients who had intracapsular cataract extractions with anterior chamber IOLs were three times w likely to show proliferative retinopathy as those who had extracap ular cataract extractions with posterior chamber IOLs. Insulindependent patients were three to four times more likely to show progression to proliferation than noninsulin dependent patients. We conclude that, while some procedures are riskier for the diabetic eye, extracapsular lens extraction with implantation of a posterior chamber lens does not imply an increased risk of development of proliferative retinopathy.

The Marcus Gunn Pupil in Experimental Tract Lessons

Isolated surgical lesions were made in three Macaca mulatta monkeys. Two had right optic tract section. One control underwent section of the right half of the chiasm. Preoperative evaluation revealed no fundus, pupil, or VER abnormalities. Postoperatively, a classic Marcus Gunn pupil was found contralateral to the isolated optic tract lesions. The control had normal pupils. The nature of the lesions was documented histopathologically, the pupillary findings, photographically. Possible explanations are explored. Contrary to traditional teaching, lesions occurring posterior to the chiasm may indeed produce the Marcus Gunn pupillary phenomenon.

Early Loss of Central Visual Acuity in Glaucoma

Central visual acuity is usually maintained until late in the course of glaucoma. Ten patients (5 men, 5 women) between the ages of 25 and 79 were found to have decreased visual acuity associated with central or centrocaecal scotomas early in their course. Five patients had chronic open-angle glucoma, three and pigmentary glaucoma, one and juvenile glaucoma, and one had Axenfelds syndrome. A Marcus Gunn pupil was present in all six patients not on miotics. Most lost central acuity at pressures under 30 mmHg. Seven patients had vision of 20/200 or less. All with marked visual loss had a cup disc rate of .8 or greater. Other causes were carefully ruled out. Proposed mechanisms for the development of these central defects include either double Bjerrum scotomas which extend centrally or early papillomacular bundle involvement due to temporal cupping. This study demonstrates that decreased vision with associated central field loss can be a relatively early finding in glaucoma.