Biomedical subjects

David L Guyton

Publications and source records attributed to David L Guyton.

17 recordsLinked to original sources

PubMed2006

"Inverted Brown pattern": a tight inferior oblique muscle masquerading as a superior oblique muscle underaction--clinical characteristics and surgical management.

PURPOSE: To characterize, and evaluate the surgical management of, patients with unilateral deficiency of depression in adduction, suggesting superior oblique muscle underaction, without significant ipsilateral inferior oblique muscle overaction. METHODS: Such patients were identified who also had received either ipsilateral inferior oblique (IO) muscle weakening or contralateral inferior rectus muscle recession. Their histories, motility patterns, intraoperative findings, types of strabismus surgery, and postoperative results were analyzed. RESULTS: Twelve patients were identified with unilateral deficiency of depression in adduction, with no or minimal ipsilateral IO muscle overaction. Three of these patients (25%) had previously had surgery for Brown syndrome. Four (33%) had prior orbital floor trauma. On exaggerated forced duction testing recorded for nine patients, a tight IO muscle was recorded in 78%, with no laxity of the superior oblique tendon. Four patients (33%) underwent contralateral inferior rectus muscle recession, but in all four the deficiency of depression in adduction recurred. The other eight (67%) had an IO muscle weakening procedure and achieved overall improvement of ocular alignment. Nine subsequent patients with a similar pattern of misalignment were each managed with an IO weakening procedure, with good results. CONCLUSIONS: This motility pattern, which we are calling an "inverted Brown pattern," is caused by a tight or inelastic IO muscle. In such cases, IO muscle weakening yields better results than contralateral inferior rectus muscle recession, even though there is no significant IO muscle overaction preoperatively.

Adolescent↗

PubMed2006

The 10th Bielschowsky Lecture. Changes in strabismus over time: the roles of vergence tonus and muscle length adaptation.

Patients with long-standing unilateral strabismus, such as "sensory" exotropia in the absence of fusion, or esotropia with unilateral amblyopia, typically show bilateral deviations under anesthesia, often symmetric. Forced ductions usually show symmetric muscle tightness. Changes in extraocular muscle lengths thus appear to occur primarily bilaterally, whether fusion is present or not. With skeletal muscles responding to changes in stimulation by the gain or loss of sarcomeres, it is likely that abnormal or unguided vergence tonus, which changes the lengths of the extraocular muscles bilaterally, is largely responsible for changes in the angle of strabismus over time. This mechanism helps explain the development of [1] increasing "basic" deviations in accommodative esotropia; [2] torsional deviations with apparent oblique muscle "overaction/underaction" and A and V patterns; [3] recurrent esotropia with early presbyopia; [4] occasional divergence insufficiency in presbyopes; and [5] basic cyclovertical deviations that mimic superior oblique muscle paresis.

Adaptation, Ocular↗

PubMed2005

Esotropia associated with early presbyopia caused by inappropriate muscle length adaptation.

BACKGROUND: The purpose of this study is to investigate the occurrence of esotropia accompanying early presbyopia. The two primary long-term mechanisms for maintenance of ocular alignment are vergence adaptation (neurologic) and muscle length adaptation (anatomic). Both mechanisms depend upon disparity-driven motor fusion for proper operation. A possible cause for an esotropic shift in early presbyopic adults with insufficient or absent disparity-driven motor fusion is inappropriate muscle length adaptation (medial rectus muscle shortening) occurring in response to increased convergence tonus accompanying increased accommodative effort. METHODS: Of 617 patients, age 10 and older who underwent surgery for esotropia during the period of 1980 to 1996, the age when the deviation occurred or worsened could be determined with confidence in 140. A plot was made of the number of these patients versus the age of onset of the deviation. This was compared with a similar plot of patients operated for exotropia. RESULTS: A statistically significant increase (P = 0.017) in the incidence of an esotropic shift in the age range from 30 to 50 years was found when compared with the incidence of an exotropic shift. CONCLUSION: If the postulated mechanism is correct, full correction of any hyperopia as well as prompt prescription of a reading add (or conversion to monovision correction) may help prevent further progression of small esodeviations accompanying early presbyopia.

Accommodation, Ocular↗

PubMed2005

Rapid, objective detection of cataract-induced blur using a bull's eye photodetector.

PURPOSE: To determine whether optical aberrations caused by cataract can be detected and quantified objectively using a newly described focus detection system (FDS). SETTING: The Wilmer Opthalmological Institute, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA. METHODS: The FDS uses a bull's eye photodetector to measure the double-pass blur produced from a point source of light. To determine the range and level of focus, signals are measured with a series of trial lenses in the light path selected to span the point of best focus to generate focus curves. The best corrected visual acuity (BCVA), refractive error, lens photograph grades, and FDS signals were obtained in 18 patients scheduled to have cataract surgery. The tests were repeated 6 weeks after surgery. RESULTS: The mean FDS outcome measures improved after cataract surgery, with increased peak height (P=.001) and decreased peak width (P=.001). Improvement in signal strength (integral of signal within +/-1.5 diopters of the point of best focus) strongly correlated with improvement in peak height (R(2)=.88, P<.0001) and photographic cataract grade (R(2)=.72, P<.0001). The mean BCVA improved from 20/50 to 20/26 (P<.0001). The improvement in BCVA correlated more closely with FDS signal strength (R(2)=.44, P=.001) than with cataract grade (R(2)=.25, P=.06). CONCLUSIONS: Improvement in FDS outcome measures correlated with cataract severity and improvement in visual acuity. This objective approach may be useful in long-term studies of cataract progression.

Aged↗

PubMed2005

The dragged-fovea diplopia syndrome: clinical characteristics, diagnosis, and treatment.

PURPOSE: To identify the clinical characteristics of the dragged-fovea diplopia syndrome, to introduce a simple diagnostic test that aids in the evaluation of such patients, and to provide a simple treatment option to improve the diplopia in some of these patients. DESIGN: Retrospective, observational case series. PARTICIPANTS: Ninety-five affected eyes in 83 consecutive patients seen between January 1, 1993, and August 9, 2004, who were diagnosed with the dragged-fovea diplopia syndrome at one institution. METHODS: We reviewed the records of 222 patients who have been seen in the Krieger Children's Eye Center at The Wilmer Institute since 1993 with a diagnosis of maculopathy, internal limiting membrane, or dragged fovea. We collected ocular findings and history for those patients who reported binocular diplopia that was not amenable to prism therapy and not secondary to acquired strabismus. MAIN OUTCOME MEASURES: We recorded the presence of metamorphopsia on Amsler grid testing or other clinical evidence of macular wrinkling, response to prism trial, response to the small-field central fusion test (lights on-off test), and response to partial occlusion with Scotch Satin tape (3M Co., St. Paul, MN). RESULTS: Ninety-five affected eyes in 83 patients met the criteria for inclusion in the study. All patients who were tested with the lights on-off test (n = 69) responded positively, demonstrating rapid central fusion with room lights off, and recurrence of central diplopia with peripheral fusion with room lights on. Forty-six patients (of 64 tested) were receptive to monocular occlusion with Scotch Satin tape. CONCLUSIONS: The dragged-fovea diplopia syndrome consists of central diplopia in the presence of peripheral fusion, secondary to dragging of the fovea in one or both eyes by retinal disease. The central diplopia cannot be eliminated by prism therapy or eye muscle surgery. The lights on-off test has proved pathognomonic for this syndrome, and many patients have benefited from partial monocular occlusion with Scotch Satin tape.

Adult↗

PubMed2005

Postoperative adjustable surgery of the superior oblique tendon.

PURPOSE: To describe a surgical procedure for loosening or tightening the superior oblique (SO) tendon that enables bedside adjustment following the surgery, with surgical outcome reported. METHODS: A permanent suture separates the two cut ends of the SO tendon, with a sliding noose for adjustment. The noose is accessed by having the patient look up or straight ahead, not down, during adjustment at the bedside. Records of 17 patients who underwent this surgery between June 2000 and January 2003 were reviewed and analyzed for outcome. RESULTS: Seventeen patients, 18 eyes, mean age 43.7 years (range 5.9 to 71 years) had SO surgery with postoperatively adjustable sutures. Twelve eyes of 11 patients had a loosening procedure, and six eyes had a tightening procedure. Seven of the patients had had precious eye muscle surgery, four having had previous surgery on the same SO tendon. All but one patient returned for the follow-up examination, ranging from 1.5 to 7 months postoperatively. Torsional imbalances in 12 patients improved in all but two. In four patients with a preoperative A pattern, the A pattern improved from 16 PD to 0 PD on average. In eight patients with vertical misalignment in straight ahead gaze who had no other cyclovertical muscle surgery simultaneously, the mean reduction was 7 PD. All patients except one had improvement in preoperative symptoms. CONCLUSION: Both loosening and tightening procedures can be performed successfully using a postoperative adjustment technique for the SO tendon.

Adolescent↗

PubMed2005

A small-incision muscle hook for the Parks cul-de- sac approach for strabismus surgery.

BACKGROUND: One of Dr. Marshall Parks' most valuable contributions to strabology was his cul-de-sac ("fornix") approach to strabismus surgery. This approach provides better comfort, faster healing and less conjunctival scarring than previous approaches. Tearing of the conjunctiva can occur, however, especially in older patients with thin and friable conjunctival tissues. METHODS: To facilitate the cul-de-sc approach through a small incision, especially in older patients, I designed a new "small-incision" muscle hook. RESULTS: A new sharp second bend combined with sharpening of the bend in the heel (creating literally an "S" bend) in the Jameson style eye muscle hook enables burying of the knee or heel of the hook in the wound, allowing reflection of the conjunctiva over the ball or toe of the hook without tearing. I have used and treasured this hook for over six years, routinely using the cul-de-sac approach to strabismus surgery in both children and adults. CONCLUSIONS: This new small- incision muscle hook complements the cul-de-sac approach to strabismus surgery by allowing the use of a smaller incision while significantly decreasing the risk of conjunctival tearing.

Equipment Design↗

PubMed2004

Strabismus following posterior segment surgery.

Persistent diplopia following posterior segment surgery is not uncommon. There are several causes of postoperative strabismus, some of which are preventable. Knowledge of the possible causes, proper evaluation, and appropriate treatment can eliminate or at least reduce the morbidity from this unwelcome postoperative surprise.

Humans↗

PubMed2004

Substrates of negative accommodation.

Negative accommodation refers to a unique phenomenon, sparsely documented in rare individuals, whereby evanescent increases in vision (described as "flashes" of clear vision) accompany a decrease in the overall plus power of the eye. Complementing less than a handful of dated studies, a few recent personal communications from eye care clinicians claim to have objectively assessed negative accommodation (e.g., by retinoscopy). Whereas negative accommodation may explain informal accounts claiming occasional improved visual acuity in uncorrected myopes, its mode of operation is not established. We sketch a potential mechanism by which negative accommodation may operate, if it exists.

Accommodation, Ocular↗

PubMed2003

Automated detection of ocular alignment with binocular retinal birefringence scanning.

We previously developed a retinal birefingence scanning (RBS) device to detect eye fixation. The purpose of this study was to determine whether a new binocular RBS (BRBS) instrument can detect simultaneous fixation of both eyes. Control (nonmyopic and myopic) and strabismic subjects were studied by use of BRBS at a fixation distance of 45 cm. Binocularity (the percentage of measurements with bilateral fixation) was determined from the BRBS output. All nonstrabismic subjects with good quality signals had binocularity >75%. Binocularity averaged 5% in four subjects with strabismus (range of 0-20%). BRBS may potentially be used to screen individuals for abnormal eye alignment.

Automation↗

PubMed2003

Transient central retinal artery occlusion after posterior sub-Tenon's anesthesia.

Two cases of transient central retinal artery occlusion were observed preoperatively after uneventful sub-Tenon's infusion of local anesthetic for cataract surgery and intraocular lens implantation. In these eyes, the retinal circulation reperfused spontaneously before surgery and there were no visual sequelae. A third case was observed in an eye after strabismus surgery with sub-Tenon's anesthesia. The patient was left with profound visual loss in this eye. The cause of this complication is unknown, but possible factors include mechanical pressure from the bolus of the anesthetic solution or localized vasoconstriction from the anesthetic, producing a decrease in ocular blood flow. Suggestions to avoid this problem include not inserting the cannula too posteriorly, not injecting forcibly against resistance, and using the minimum volume of anesthetic possible.

Adult↗

PubMed2003

Astigmatism induced by simultaneous recession of both horizontal rectus muscles.

PURPOSE: Changes have been reported in the refractive state of the eye after various types of strabismus surgery. This study investigates the effect of large simultaneous recession of both horizontal rectus muscles on the refractive state of the eye. METHODS: Twenty-six eyes (13 patients) were refracted 1 to 2 weeks before and 6 to 8 weeks after large horizontal rectus muscle recessions for the purpose of damping nystagmus. The preoperative refraction was mathematically subtracted from the postoperative refraction, and the induced refractive changes were averaged and statistically analyzed. The relation between the amount of recession and the induced astigmatism was also investigated. RESULTS: A statistically significant change in astigmatism in the with-the-rule direction was induced with this procedure (+ 0.70 diopter cylinder, axis 90.0 degrees, P <.0002). With the narrow range of amounts of recession performed, there was no demonstrable relation between the amount of recession and the amount of induced astigmatism. CONCLUSIONS: Recession of both horizontal rectus muscles, the same as has been reported for recession of one horizontal rectus muscle and recession-resection surgery on both horizontal rectus muscles, tends to induce a change in astigmatism in the with-the-rule direction.

Adolescent↗

PubMed2003

Primary position and listing's law in acquired and congenital trochlear nerve palsy.

PURPOSE: In ocular kinematics, the primary position (PP) of the eye is defined by the position from which movements do not induce ocular rotations around the line of sight (Helmholtz). PP is mathematically linked to the orientation of Listing's plane. This study was conducted to determine whether PP is affected differently in patients with clinically diagnosed congenital (conTNP) and acquired (acqTNP) trochlear nerve palsy. METHODS: Patients with unilateral conTNP (n = 25) and acqTNP (n = 9) performed a modified Hess screen test. Three-dimensional eye positions were recorded with dual search coils. RESULTS: PP in eyes with acqTNP was significantly more temporal (mean: 21.2 degrees ) than in eyes with conTNP (6.8 degrees ) or healthy eyes (7.2 degrees ). In the pooled data of all patients, the horizontal location of PP significantly correlated with vertical noncomitance with the paretic eye in adduction (R = 0.59). Using a computer model, PP in acqTNP could be reproduced by a neural lesion of the superior oblique (SO) muscle. An additional simulated overaction of the inferior oblique (IO) muscle moved PP back to normal, as in conTNP. Lengthening the SO and shortening the IO muscles could also simulate PP in conTNP. CONCLUSIONS: The temporal displacement of PP in acqTNP is a direct consequence of the reduced force of the SO muscle. The reversal of this temporal displacement of PP, which occurs in some patients with conTNP, can be explained by a secondary overaction of the IO muscle. Alternatively, length changes in the SO and IO muscles, or other anatomic anomalies within the orbit, without a neural lesion, may also explain the difference in location of PP between conTNP and acqTNP.

Adaptation, Ocular↗

PubMed2002

Motor mechanisms of vertical fusion in individuals with superior oblique paresis.

PURPOSE: We wanted to determine the mechanisms of motor vertical fusion in patients with superior oblique paresis and to correlate these mechanisms with surgical outcomes. METHODS: Ten patients with superior oblique paresis underwent 3-axis, bilateral, scleral search coil eye movement recordings. Eye movements associated with fusion were analyzed. RESULTS: Six patients had decompensated congenital superior oblique paresis and 4 had acquired superior oblique paresis. All patients with acquired superior oblique paresis relied predominantly on the vertical rectus muscles for motor fusion. Patients with congenital superior oblique paresis were less uniform in their mechanisms for motor fusion: 2 patients used predominantly the oblique muscles, 2 patients used predominantly the vertical recti, and 2 patients used predominantly the superior oblique in the hyperdeviated eye and the superior rectus in the hypodeviated eye. The last 2 patients developed the largest changes in torsional eye alignment relative to changes in vertical eye alignment and were the only patients to develop symptomatic surgical overcorrections. CONCLUSION: There are 3 different mechanisms for vertical fusion in individuals with superior oblique paresis, with the predominant mechanism being the vertical recti. A subset of patients with superior oblique paresis uses predominantly the superior oblique muscle in the hyperdeviated paretic eye and the superior rectus muscle in the fellow eye for fusion. This results in intorsion of both eyes, causing a large change in torsional alignment. The consequent cyclodisparity, in addition to the existing vertical deviation, may make fusion difficult. The differing patterns of vertical fusional vergence may have implications for surgical treatment.

Adolescent↗

PubMedDate not supplied

Automated detection of ocular focus.

We characterize objectively the state of focus of the human eye, utilizing a bull's eye photodetector to detect the double-pass blur produced from a point source of light. A point fixation source of light illuminates the eye. Fundus-reflected light is focused by the optical system of the eye onto a bull's eye photodetector [consisting of an annulus (A) and a center (C) of approximately equal active area]. To generate focus curves, C/A is measured with a range of trial lenses in the light path. Three human eyes and a model eye are studied. In the model eye, the focus curve showed a sharp peak with a full width at half maximum (FWHM) of +/-0.25 D. In human eyes, the ratio C/A was >4 at best focus in all cases, with a FWHM of +/-1 D. The optical apparatus detects ocular focus (as opposed to refractive error) in real time. A device that can assess focus rapidly and objectively will make it possible to perform low-cost, mass screening for focusing problems such as may exist in children at risk for amblyopia.

Diagnosis, Computer-Assisted↗

PubMedDate not supplied

Pediatric Vision Screener 1: instrument design and operation.

We develop the Pediatric Vision Screener (PVS) to automatically detect ocular misalignment (strabismus) and defocus in human subjects. The PVS utilizes binocular retinal birefringence scanning to determine when both eyes are aligned, with a theoretical accuracy of <1 deg. The device employs an autoconjugate, bull's-eye detector-based system to detect focus. The focus and alignment pathways are separated by both wavelength and data acquisition timing. Binocular focus and alignment are detected in rapid alternating sequence, measuring both parameters in both eyes in <0.5 sec. In this work, the theory and design of the PVS are described in detail. With objective, automated measurement of both alignment and focus, the PVS represents a new approach to screening children for treatable eye disease such as amblyopia.

Adult↗

PubMedDate not supplied

Pediatric Vision Screener 2: pilot study in adults.

Amblyopia is a form of visual impairment caused by ocular misalignment (strabismus) or defocus in an otherwise healthy eye. If detected early, the condition can be fully treated, yet over half of all children with amblyopia under age 5 escape detection. We developed a Pediatric Vision Screener (PVS) to detect amblyopia risk factors. This instrument produces a binocularity score to indicate alignment and a focus score to indicate focus. The purpose of this study is to assess the performance of the PVS by testing adults who were fully cooperative for testing. The study group includes 40 subjects (20 controls, 20 patients) aged 22 to 79 years. 12 patients had constant strabismus (8 to 50Delta), and eight had variable strabismus (12 to 55Delta). All controls had binocularity scores >50%. Binocularity was <50% in 11/12 patients. The patient with binocularity >50% had a well-controlled intermittent exotropia and was not at risk for amblyopia. Focus scores were highly sensitive for good focus but not specific. The PVS shows high sensitivity and specificity for detection of strabismus in adults. Future studies will determine whether this performance can be achieved in preschool children, who are at greatest risk for vision loss.

Adult↗