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D L Guyton

Publications and source records attributed to D L Guyton.

At least 19 recordsLinked to original sources
PubMed2001

Photographic reproduction of out-of-focus and distorted ocular imagery.

The necessary settings and parameters were determined for ordinary camera and lens systems to faithfully reproduce out-of-focus and distorted imagery as it falls upon the retina of the human eye. Theoretic considerations of both geometric and physical optics were used to calculate the "relative blur" and distortion produced by refractive error added to ordinary camera lenses as opposed to refractive error in an arbitrary thick-lens optical system bounded by air and fluid (i.e. the eye). In both the camera and the eye, "relative blur" was determined to be directly proportional to dioptric defocus and to aperture size, and effectively independent of the focal length. Distortion of imagery was also found to be independent of the focal length. Photographs corroborate the theoretic findings. A given amount of relative blur, however, appeared somewhat greater when recorded on photographic film than when appreciated by the human eye. The Stiles-Crawford effect, the chromatic aberration of the eye, and neural processing probably each contribute to this difference. Previous investigators have grossly exaggerated blur and distortion in photographs intended to simulate ocular imagery and have drawn misleading conclusions from their results.

Humans↗
PubMed2001

An adjustable superior oblique tendon spacer with the use of nonabsorbable suture.

PURPOSE: Philip Knapp described a method, sometimes referred to as the "chicken suture,"of securing a loose nonabsorbable suture to the cut ends of the superior oblique tendon to facilitate future reversal. The purpose of this study is to describe a modification of Knapp's technique to achieve partial, reversible, and intraoperatively adjustable superior oblique weakening. METHODS: The superior oblique tendon was exposed, 2 polyester nonabsorbable sutures were placed 4 mm apart, and the tendon was cut. With the use of a slip knot, the cut ends of the tendon were separated by 2 to 8 mm. Tendon separation was adjusted intraoperatively according to the exaggerated traction test and, in some cases, fundus torsion. Medical records of all patients who underwent surgery with this technique were reviewed and the outcomes tabulated. RESULTS: Twelve patients (16 eyes) were treated for superior oblique overaction and 3 patients (3 eyes) for Brown syndrome. Follow-up was 2 to 46 months (mean, 17 months). Mean superior oblique overaction improved from +1.3 before surgery to +0.3 after surgery, mean A pattern improved from 20 PD to 2 PD, and fundus intorsion improved from +1.2 to +0.3. In Brown syndrome, the mean elevation in adduction improved from -3.8 to -1.0. One patient from each group developed an overcorrection. None of the patients developed recurrence. The patients with Brown syndrome continued to improve over a 1-year period. CONCLUSIONS: The superior oblique tendon suture spacer is effective, intraoperatively adjustable, and technically easier to perform than a silicone expander procedure. This technique should be considered as an alternative for patients requiring superior oblique weakening.

Adolescent↗
PubMed2001

Superior oblique overaction from local anesthesia for cataract surgery.

Traumatic superior oblique dysfunction from cataract surgery appears to be rare, with only 3 reported cases of postoperative Brown syndrome and 1 reported case of postoperative superior oblique weakness. We are not aware of any prior reports of superior oblique overaction occurring after cataract surgery. We describe a patient with acquired superior oblique overaction as a cause of vertical strabismus after cataract surgery. Ocular torsion analysis was essential in localizing the malfunction to the superior oblique muscle. The most likely etiology is myotoxicity from inadvertent intramuscular injection of local anesthetic before cataract surgery.

Anesthesia, Local↗
PubMed2000

Perception of Purkinje vessel shadows and foveal granular pattern as a measure of potential visual acuity.

PURPOSE: To compare perception of 2 entoptic phenomena, the Purkinje vessel shadows and the foveal granular pattern, as measures of retinal visual acuity using a transscleral illumination technique that bypasses the anterior segment. SETTING: Retinal Vascular Center and General Eye Clinic, Wilmer Ophthalmological Institute, Johns Hopkins Hospital, Baltimore, Maryland, USA. METHODS: Both eyes of 85 patients with clear ocular media, many with retinal disease, were tested for perception of these entoptic phenomena. Also, retinal visual acuity was measured with a Potential Acuity Meter through the current refractive correction. RESULTS: Of 114 eyes with retinal acuity of 20/40 or better, 99% perceived the Purkinje vessel shadows and 86% perceived the foveal granular pattern. Of 45 eyes with retinal acuity of 20/80 or worse, 73% perceived the Purkinje vessel shadows and 4% perceived the foveal granular pattern. CONCLUSION: Perception of the Purkinje vessel shadows does not distinguish between good and poor retinal acuity, whereas nonperception of the vessel shadows strongly suggests poor acuity. Perception of the foveal granular pattern, on the other hand, provides a positive indication of good retinal acuity and will likely prove to be predictive of good vision after removal of significant media opacity.

Cataract↗
PubMed2000

Anesthetic myotoxicity as a cause of restrictive strabismus after scleral buckling surgery.

PURPOSE: To explore the possibility that anesthetic myotoxicity may play a role in restrictive strabismus following scleral buckling procedures. METHODS: The authors performed a retrospective study of patients who presented with strabismus following scleral buckling procedures. Details were sought regarding the scleral buckling procedure, including type and route of anesthesia. The types of strabismus were compiled, as were relevant findings at strabismus surgery. The contributing vitreoretinal surgeons were surveyed regarding the usual type and route of anesthesia used for their scleral buckling procedures. RESULTS: Over 90% of scleral buckling procedures resulting in significant strabismus were performed under local anesthesia. Of the 17 patients on whom strabismus surgery was performed, 14 had positive forced ductions. A hypodeviation of the buckled eye was the most common presentation. CONCLUSION: Based on the types, patterns, and amounts of strabismus encountered after scleral buckling procedures, and the similarity of these findings to cases of strabismus following retrobulbar anesthesia for cataract procedures, the authors propose that local anesthetic myotoxicity is often the primary cause of strabismus occurring after scleral buckling procedures for retinal detachment.

Anesthesia, Local↗
PubMed2000

Strabismus after retinal detachment surgery.

Strabismus after retinal detachment surgery is temporary in most cases. Long-term diplopia, however, is seen in 5% to 25% of patients. In most cases the cause is restrictive strabismus due to adhesions, muscle fibrosis, or scarring involving the buckling material. Deviations due to direct muscle injury and "sensory" deviations due to poor vision also occur. Nonsurgical treatments include prisms and botulinum toxin injections. Surgical intervention using adjustable sutures is successful in most cases.

Humans↗
PubMed2000

Dissociated vertical deviation: etiology, mechanism, and associated phenomena. Costenbader Lecture.

PURPOSE: The etiology and mechanism of dissociated vertical deviation (DVD) are explored. METHODS: In 6 young adults with DVD, the simultaneous horizontal, vertical, and torsional eye movements for both eyes were recorded by using dual-coil scleral search coils. Analysis of the simultaneous vertical and torsional movements that occurred during the DVD response identified the primary muscles acting in the vergences and versions involved. RESULTS: Typically, both horizontal and cyclovertical latent nystagmus developed upon occlusion of either eye. A cycloversion/vertical vergence then occurred, with the fixing eye intorting and tending to depress and the covered eye extorting and elevating. Simultaneously, upward versions occurred for the maintenance of fixation, consisting of various saccades and smooth eye movements, and this led to further elevation of the eye behind the cover. The cyclovertical component of the latent nystagmus became partially damped as the DVD developed. CONCLUSIONS: In patients with an early onset defect of binocular function, the occlusion of one eye, or even concentration on fixing with one eye, produces unbalanced input to the vestibular system. This results in latent nystagmus with a cyclovertical component, sometimes only seen with magnification. A normal, oblique-muscle-produced, cycloversion/vertical vergence then comes into play, occurring in an exaggerated form in the absence of binocular vision, probably as a learned response. This cycloversion/vertical vergence helps damp the cyclovertical nystagmus (a cyclovertical "nystagmus blockage" phenomenon), aiding vision in the fixing eye. But this mechanism also produces unavoidable and undesirable elevation and extorsion of the fellow eye, which we call DVD.

Adolescent↗
PubMed1999

Vertical fusional vergence: the key to dissociated vertical deviation.

OBJECTIVES: To test the previous findings of Enright that disparity-induced vertical vergence is mediated primarily by the oblique muscles, and to relate this normal eye movement pattern to the eye movement pattern seen in subjects with dissociated vertical deviation. METHODS: Sixteen normal volunteers underwent 55 measurements of the cycloversion associated with prism-induced vertical vergence using an afterimage apparatus. A Vernier scale measured the direction and magnitude of the torsional shift that occurred with recovery of fusion on removal of a 3- or 4-prism diopter prism. RESULTS: Of the 55 trials, the directions of torsional shift were consistent with the oblique muscles being the primary mediators of vertical fusional vergence in 51 (93%) (P = .03 using a binomial distribution). The mean +/- SD value of torsional shift was 1.15 degrees+/-0.76 degrees in the expected direction. CONCLUSIONS: Vertical fusional vergences in this study were produced primarily by the oblique extraocular muscles. The eye movement patterns of these vertical vergences in normal subjects are qualitatively similar to those seen in recordings of patients with dissociated vertical deviation. Dissociated vertical deviation thus seems to be an exaggeration of a normally occurring eye movement pattern. The cyclovertical component of dissociated vertical deviation may help stabilize the fixing eye by damping vertical nystagmus, while the accompanying hypertropia is an incidental and undesirable side effect.

Adolescent↗
PubMed1999

The Lancaster red-green test before and after occlusion in the evaluation of incomitant strabismus.

BACKGROUND: Patients with incomitant strabismus can often fuse in a limited area of gaze. Prolongation of neurologically learned fusional vergence tone ("vergence adaptation") in and near this area can result in misleading measurements with standard clinical measures of strabismus. Monocular occlusion for at least 30 minutes eliminates most of the effect of vergence adaptation. The Lancaster red-green test provides an elegant and convenient map of incomitant strabismus. We investigated the efficacy of the Lancaster red-green test before and after monocular occlusion for the investigation of incomitant strabismus. METHODS: We retrospectively studied the results of the Lancaster red-green test in 6 patients with incomitant vertical strabismus in whom we suspected that vergence adaptation might be distorting the pattern of deviation. The test was performed before and after monocular occlusion for 30 to 60 minutes, and the preocclusion and postocclusion results were compared. RESULTS: In the 6 cases studied, the Lancaster red-green test showed at least a 5-PD increase in the hyperdeviation, after monocular occlusion. The increases were mostly in primary gaze and downgaze, which tended to regularize the pattern of deviation. CONCLUSIONS: The combination of monocular occlusion and the Lancaster red-green test is useful for uncovering the effect of vergence adaptation. Such results may often simplify the planning of surgical correction because the incomitance usually decreases after monocular occlusion, making it less likely that surgery will worsen the alignment in the area previously fused. We recommend that monocular occlusion should be considered when planning surgery or even prism correction for incomitant deviations, especially when the initial Lancaster red-green test shows an unexpected incomitant pattern where there is fusion in 1 direction of gaze but not in others.

Adult↗
PubMed1999

Mathematical modeling of retinal birefringence scanning.

Retinal birefringence scanning (RBS) is a new technique that is used to detect the fixation of the eye remotely and noninvasively. The method is based on analysis of polarization changes induced by the retina. In this study, the principles of RBS were mathematically modeled to facilitate a better understanding of the origins of the signals obtained. Stokes vector analysis and Mueller matrix multiplication were augmented with Poincaré sphere representation. The cornea was modeled as a linear retarder. The foveal area was modeled as a radially symmetric birefringent medium. The model accurately predicted the frequency and phase of RBS signals obtained during central and paracentral fixation. The signal that indicates central fixation during RBS likely results from a combination of the radial birefringence of the Henle fibers and the overlying corneal birefringence.

Birefringence↗
PubMed1999

The use of (a)symmetry of the rest position of the eyes under general anesthesia or sedation-hypnosis in the design of strabismus surgery: A favorable pilot study in 51 exotropia cases.

BACKGROUND AND PURPOSE: Studies support techniques of intraoperative adjustment under general anesthesia, of eye muscle surgery, based upon the rest position (deviation) to improve surgical results. None, however, have examined the (a)symmetry, per se, of the rest position and its influence on surgical outcomes. METHODS: Retrospective/prospective patient chart data and photographs taken of patients under anesthesia were judged for (a)symmetry of deviation and correlated with (a)symmetry of surgery performed on 51 exotropic patients. Two groups were compared: "matched" (symmetrical surgery for symmetrical deviations and asymmetrical surgery for asymmetrical deviations) and "opposite" in which the reverse was performed. RESULTS: Sensory results were "statistically significantly" better (p=0.027), the need for postoperative adjustment of adjustable sutures was "statistically significantly" less (p=0.031) and the motor results tended to be improved (p=0.237) ("clinically/medically significant") when surgery was "matched" to the deviation under anesthesia. CONCLUSION: Use of the (a)symmetry of deviations under anesthesia can improve surgical results. Therefore, the final decision as to which muscles to operate on might best be delayed until the time of surgery when that (a)symmetry can be observed. This pilot study should be confirmed by a proper completely prospective randomized study.

Adolescent↗
PubMed1998

Vertical location of the corneal light reflex in strabismus photography.

OBJECTIVE: To improve the clinical documentation of strabismus by mathematically predicting and clinically verifying the location of a fixation target that produces a vertically centered corneal light reflex (first Purkinje image) in clinical photographs of the eye using a standard photographic flash unit. MATERIALS AND METHODS: Mathematical modeling of the corneal light reflex during clinical photography was based on the schematic eye. Clinical photographs were taken using a range of fixation targets located between the center of the camera lens and the center of the flash. Image quality was also assessed subjectively. RESULTS: Optimum vertical centration of the corneal light reflex was predicted and produced when the fixation target was located one fifth of the distance from the center of the flash to the center of the camera lens. Placement of the flash below, rather than above, the camera lens provided more uniform illumination of the patient's eyes and face. Decreasing the distance between the camera lens and the flash minimized the severity of these artifacts. CONCLUSIONS: A poorly positioned corneal light reflex makes it difficult to identify the fixing eye in photographs of patients with strabismus, especially when vertical strabismus is present. Adoption of the aforementioned protocol will reproduce the appearance of coaxially viewed corneal light reflexes and provide much-needed standardization for strabismus case presentation.

Blinking↗
PubMed1998

Masked bilateral superior oblique muscle paresis. A simple overcorrection phenomenon?

OBJECTIVE: This study aimed to determine a mechanism by which the masked bilateral superior oblique muscle paresis phenomenon may be explained. DESIGN: A retrospective study of the authors' patients with the preoperative diagnosis of a unilateral superior oblique muscle paresis was performed. Patients in whom an apparent contralateral superior oblique muscle paresis developed after surgery (masked bilateral superior oblique muscle paresis) were compared with those patients in whom this condition did not develop. PARTICIPANTS: One hundred eight patients participated. RESULTS: Of the 108 patients studied, 30 (27.7%) patients had signs of an apparent superior oblique muscle paresis develop in the contralateral eye after surgery. In comparing those patients in whom an apparent contralateral superior oblique muscle paresis did develop after surgery with those patients in whom this finding did not develop, no significant differences were found in the age at surgery; etiology (traumatic vs. nontraumatic); average hyperdeviations in primary gaze, ipsilateral and contralateral gazes, and ipsilateral and contralateral head tilts; average V pattern; inferior and superior oblique muscle function; extorsion on double Maddox rod testing; and objective fundus extorsion. CONCLUSION: Analysis of the authors' data showed that a surgical overcorrection of a unilateral superior oblique muscle paresis can masquerade as an apparent contralateral superior oblique muscle paresis. This is caused by a persistence of the head tilt and side gaze misalignment pattern from the original superior oblique muscle paresis.

Adult↗
PubMed1998

Dissociated vertical deviation: an exaggerated normal eye movement used to damp cyclovertical latent nystagmus.

PURPOSE: Dissociated vertical deviation (DVD) has eluded explanation for more than a century. The purpose of this study has been to elucidate the etiology and mechanism of DVD. METHODS: Eye movement recordings of six young adults with DVD were made with dual-coil scleral search coils under various conditions of fixation, illumination, and head tilt. Horizontal, vertical, and torsional eye movements were recorded for both eyes simultaneously. Analyses of the simultaneous vertical and torsional movements occurring during the DVD response were used to separate and identify the component vergence and version eye movements involved. RESULTS: Typically, both horizontal and cyclovertical latent nystagmus developed upon occlusion of either eye. A cycloversion then occurred, with the fixing eye intorting and tending to depress, the covered eye extorting and elevating. Simultaneously, upward versions occurred for the maintenance of fixation, consisting variously of saccades and smooth eye movements, leading to further elevation of the eye behind the cover. The cyclovertical component of the latent nystagmus became partially damped as the DVD developed. CONCLUSIONS: In patients with an early-onset defect of binocular function, the occlusion of one eye, or even concentration on fixing with one eye, produces unbalanced input to the vestibular system. This results in latent nystagmus, sometimes seen only with magnification. The cyclovertical component of the latent nystagmus, when present, is similar to normal vestibular nystagmus induced by dynamic head tilting about an oblique axis. Such vestibular nystagmus characteristically produces a hyperdeviation of the eyes. In the case of cyclovertical latent nystagmus, the analogous hyperdeviation will persist unless corrected by a vertical vergence. A normal, oblique-muscle-mediated, cycloversion/vertical vergence is called into play. This occurs in the proper direction to correct the hyperdeviation, but it occurs in an exaggerated form in the absence of binocular vision, probably as a learned response. The cycloversion/vertical vergence helps damp the cyclovertical nystagmus (a cyclovertical "nystagmus block-age" phenomenon), aiding vision in the fixing eye. But this mechanism also produces unavoidable and undesirable elevation and extortion of the fellow eye, which we call DVD.

Adaptation, Physiological↗
PubMed1997

Full-time atropine, intermittent atropine, and optical penalization and binocular outcome in treatment of strabismic amblyopia.

OBJECTIVE: The purpose of the study is to evaluate the monocular and binocular outcome of three types of "penalization" (blurring of the sound eye) treatment of amblyopia: traditional full-time atropine or optical penalization and a new intermittent atropine regimen involving atropine instillation 1 to 3 days a week. DESIGN: The study design was a retrospective study. PARTICIPANTS: A total of 163 patients with strabismic amblyopia treated by full-time atropine (n = 38), intermittent atropine (n = 73), or optical (n = 52) penalization participated. MAIN OUTCOME MEASURES: Logarithm of the minimum angle of resolution (logMAR) visual acuity, and binocularity index were determined. RESULTS: All three forms of penalization produced statistically significant mean reduction in amblyopia (1.7-2.7 logMAR lines) and mean improvement in binocularity by the end-of-treatment or long-term follow-up visit or both, with minimal mean loss after discontinuation or slight mean improvement on these measures at long-term mean follow-up of 1.9 to 4 years across groups. Few patients achieved high-grade stereoacuity. Compliance was high. Comparable efficacy was found for all three treatment groups after controlling for age, depth of amblyopia, and binocularity at the initial visit. Initial-visit amblyopia depth was strongly and significantly associated with amblyopia depth at both post-treatment visits. Pretreatment and post-treatment binocularity showed a similar strong relationship. Surprisingly, however, there was no consistent or significant association found between depth of amblyopia and binocularity in any visit combination. Post-treatment measures of these two variables also were not associated with initial-visit age or refractive error at any clinically significant level. Mean treatment duration was 1.1 to 2.9 years and was not found to be associated with visual outcome. Amblyopia reversal was found in one (full-time atropine) case at a clinically important level. CONCLUSIONS: The authors confirmed previous reports of penalization's efficacy as a primary treatment of moderate amblyopia (20/100 or better acuity) and, in some cases, relatively severe amblyopia (>20/100) and also confirmed its ability to significantly improve mean binocularity. Amblyopia and binocularity appear to respond to treatment independently and, within the postinfancy age range of the sample studied, the responses appear to be independent of initial-visit age. The high acceptability to patients and parents of atropine penalization, and particularly of the intermittent regimen introduced here, suggests the need for prospective-study-based re-evaluation of the relative merits of penalization and occlusion as the standard of care for mild-to-moderate amblyopia.

Accommodation, Ocular↗