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Biomedical subjects

D L Guyton

Publications and source records attributed to D L Guyton.

At least 19 recordsLinked to original sources
PubMed1995

Inferior oblique muscle injury from local anesthesia for cataract surgery.

BACKGROUND: Vertical rectus muscle injury is commonly cited as a cause of strabismus after cataract surgery. Injury to the inferior oblique muscle or nerve as a complication of cataract surgery has not been described previously. METHODS: Four patients without pre-existing strabismus who had diplopia after cataract surgery were studied. Analysis included prism and cover testing, Lancaster red-green testing, and fundus torsion assessment. RESULTS: Three patients had a delayed-onset hypertropia with fundus extorsion in the eye that underwent surgery, which is consistent with inferior oblique muscle overaction secondary to presumed contracture. The fourth patient had an immediate-onset hypotropia with fundus intorsion in the eye that underwent surgery, which is consistent with inferior oblique muscle paresis. Damage to a vertical rectus muscle or "unmasking" of a pre-existing superior oblique muscle paresis could not explain the history and findings in this group of four patients. CONCLUSION: The inferior oblique muscle contracture observed in three patients may have been caused by local anesthetic myotoxicity, whereas the paresis observed in one patient may have been due to mechanical trauma or anesthetic toxicity directly to the nerve innervating the muscle. Inferior oblique muscle or nerve injury should be considered as another possible cause of postoperative strabismus, especially when significant fundus torsion accompanies a vertical deviation.

Aged↗
PubMed1995

Quantification of the Brückner test for strabismus.

PURPOSE: To measure quantitatively the change in the coaxial fundus reflex with varying degrees of ocular misalignment. METHODS: The coaxial fundus reflex was imaged with a charge coupled device camera under conditions of simulated ocular misalignment ranging from 0 degrees to 7 degrees of fixation eccentricity. The effects of refractive error and pupil size were controlled. Average gray scale brightness values were calculated for each bright pupil image after some image processing was performed on the raw images. RESULTS: A reliable, sharply delineated, minimum brightness at foveal fixation was observed. CONCLUSIONS: It is estimated that this technique can be automated to detect the presence of 2 degrees to 3 degrees of ocular misalignment based on the difference in brightness of the bright pupil images between the two eyes.

Adult↗
PubMed1991

Optimal astigmatism to enhance depth of focus after cataract surgery.

A small amount of myopic astigmatism can enhance the depth of focus of the pseudophakic eye, optimally providing at least 20/30 visual acuity for both near and distance fixation. For given spherocylindrical refractive errors and fixation distances, the cross-sectional area of Sturm's conoid at the retina was calculated for a schematic eye. These data were used to determine the optimal astigmatic error needed to obtain maximum depth of focus and least theoretical blur for any given spherical equivalent refractive error. Optimal depth of focus was obtained when the plus cylindrical component equaled negative sphere - 0.25 diopters. The near and distance visual acuities of ten pseudophakic patients with induced refractive errors were highly correlated with this model. Low myopic astigmatism after cataract surgery may represent an alternative to multifocal intraocular lenses by providing spectacle independence.

Astigmatism↗
PubMed1991

Disconjugate adaptation to long-standing, large-amplitude, spectacle-corrected anisometropia.

A 12-yr-old anisometropic patient had worn corrective eyeglasses (right eye, -0.50 +1.50 x 125; LE, -9.75 +2.50 x 60) for 7 yr, and then changed to contact lenses. Eye movements were recorded before and after the change to contact lenses using binocular search coils. In habitual spectacle viewing, the patient showed disconjugate adaptation. During monocular viewing, for example, ocular alignment changed by as much as 4 degrees during a 20 degrees saccade. Also, during monocular viewing, with either eye, placing the spectacle lens in front of the eye caused an increase in the disconjugate adaptive response compared with viewing without lenses. This finding emphasizes the context specificity of adaptive responses. After switching to contact lenses, the patient still wore his spectacles for 20-40 min each day. Although there was little residual disconjugate adaptation for vertical saccades, he showed considerable adaptation for horizontal saccades, especially for gaze changes that required divergence. The persistence of a partial state of disconjugate adaptation allowed the patient to use immediate, disparity-induced, horizontal vergence to aid ocular alignment in either the contact-lens-viewing or the spectacle-viewing condition. A more complete reversion to conjugacy occurred after nine days of exclusive use of his contact lenses. Then, in a short-term experiment, two minutes of binocular viewing through the eyeglasses induced a considerable reversion toward the previous state of disconjugate adaptation (up to 1.25 degrees of vergence change during monocular viewing). Finally, the waveform of the adapted (to spectacles) intrasaccadic vergence change with monocular viewing was similar to the waveform of the unadapted intrasaccadic vergence change during binocular refixations between targets that required a combined saccade and vergence. This finding suggests a common mechanism for adaptation to spectacle-corrected anisometropia and for normal binocular vergence-saccade interactions.

Adaptation, Ocular↗
PubMed1990

Rapid determination of intraocular lens tilt and decentration through the undilated pupil.

The apparent optical axis of an implanted intraocular lens (IOL) can be located by alignment of the examiner's hand light with the third and fourth Purkinje images from the front and back surfaces of the IOL. Tilt of the IOL can be estimated (or measured with an arc perimeter) by the angle between the apparent optical axis and the patient's line of sight (actual tilt approximately 0.85 x apparent tilt). Decentration of the IOL is easily detected, equal to the distance of the IOL optical axis from the center of the pupil. This simple technique can be used through the natural pupil with posterior chamber IOLs, providing the optical axis of the malpositioned IOL still passes through the pupil.

Humans↗
PubMed1990

A primate model of anterior segment ischemia after strabismus surgery. The role of the conjunctival circulation.

Fornix conjunctival incisions in strabismus surgery may provide partial protection against anterior segment ischemia by preserving the perilimbal conjunctival-Tenon's circulation, which is disrupted with limbal conjunctival incisions. Six adult cynomolgus monkeys underwent tenotomies of three or four rectus muscles by making limbal conjunctival incisions in one eye and fornix incisions in the other. Iris fluorescein angiography and slit-lamp biomicroscopy were used to monitor changes. The eyes that had limbal incisions exhibited more severe anterior segment ischemic changes than the eyes that had fornix incisions in every instance of four rectus muscle surgery.

Animals↗
PubMed1990

Esotropia following bilateral lateral orbital decompressions for Graves' disease.

A 48-year-old woman with mild Graves' orbitopathy underwent bilateral lateral orbital decompressions through preauricular hairline incisions by a general plastic surgeon. Immediately postoperatively she developed marked left orbital and eyelid edema and incapacitating diplopia due to a large angle esotropia and severe bilateral abduction deficits. Examination 13 months later revealed normal visual acuities and a 90 prism diopter esotropia. She underwent complex strabismus surgery with resultant orthophoria in primary and down gaze. Four years later, a thin section computed tomographic scan revealed severe attenuation of both lateral rectus muscles with incarceration of the muscle bellies into the lateral osteotomy sites. This case demonstrates a rare, but avoidable, complication of orbital surgery for Graves' disease.

Esotropia↗
PubMed1989

Aphakic reading adds. An error in traditional teaching.

It is traditionally taught in ophthalmic optics that the "effective" bifocal add is greater than the prescribed add in aphakic spectacles. Because the reading segment is fabricated on the front surface of the lens, the added back vertex power is significantly greater than the prescribed add. It is taught that the effective power should be measured at the back surface. The authors explain informally why the effective add is, in truth, exactly equal to the prescribed add and not equal to the difference in back vertex power between the top and bottom segments. Practitioners who prescribe spectacles by the traditional teaching may leave their aphakic patients with suboptimal reading vision.

Aphakia↗
PubMed1989

Dark-rearing interference with emmetropization in the rhesus monkey.

Dark rearing has been shown to protect against the development of lid-suture myopia in monkeys and tree shrews. Dark-reared monkeys and cats, with or without lid suture, are significantly hyperopic in comparison to light-reared controls. The time course of refractive change during dark rearing has only been systematically investigated in chicks, with hyperopia increasing from 14 to 42 days after hatching. Longitudinal refractions of dark-reared monkeys have not been reported previously. Five infant rhesus monkeys were dark reared with their mothers from the first day of life until 58 to 161 days of age. Cycloplegic retinoscopies were performed at 2-week intervals and were compared with cross-sectional data from 18 normal monkeys at ages 1 to 81 days. The normal monkeys typically had hyperopic refractions from +4 to +8 diopters at birth with an average refraction of +2.8 diopters between 30 and 81 days of age, compared with an average refraction of +5.3 diopters between 30 and 81 days of age for the monkeys raised in darkness (difference significant at P less than 0.05). Three of the dark-reared animals retained an average of 7.0 diopters of hyperopia. Darkness thus slowed or interrupted the normal loss of hyperopia in three of the five experimental subjects, and may be useful for creating model hyperopic animals on the order of +5 to +8 diopters.

Aging↗
PubMed1988

Monocular diplopia accompanying ordinary refractive errors.

Monocular diplopia is commonly encountered in ophthalmic practice. We discovered that it could be induced in nine (82%) of 11 normal eyes with ordinary spherical or astigmatic defocus of the retinal image. Possible mechanisms responsible for this effect include retinal processing, diffraction effects, and spherical aberration. By employing geometric blur circle theory and using a simple optical model to photograph the effect, we concluded that monocular diplopia in the setting of ordinary refractive error is secondary to relatively minor optical irregularity such as spherical aberration. Contour enhancement properties of the retina probably accentuate this effect. Ordinary refractive error should therefore not be overlooked or discounted in patients with monocular diplopia.

Adult↗
PubMed1988

Ocular torsion: sensorimotor principles.

Eye movements are basically limited to two degrees of freedom, as described by Donders' and Listing's laws. Complex patterns of innervation maintain the geometric constancy of the retinal meridians, presumably via visual feedback acting through orientation-specific neurons in the cortex. Interactions between torsional and vertical movements of the eyes can be demonstrated by stimulating ocular torsion and detecting secondary vertical deviations. Geometric considerations show that significant peripheral disparities occur with convergence and eye movements, dictating large Panum's fusional areas in the periphery. Good visual acuity in man must thus be limited to the fovea, but the large peripheral Panum's fusional areas allow sensory cyclofusion of up to 8 degrees. In addition, motor cyclofusion occurs in the presence of large-field stimuli, further helping to minimize problems from torsional diplopia both in normal individuals and in patients with ocular motor pareses.

Convergence, Ocular↗
PubMed1988

Comparison of hang-back medial rectus recession with conventional recession.

Hang-back recession is commonly used for adjustable strabismus surgery and surgery for dissociated vertical deviation. The authors have begun to use the hand-back technique for routine recessions as well, to simplify the procedure and to lessen the risk of scleral perforation. In 49 consecutive children undergoing conventional bilateral medial rectus recession and 31 consecutive children undergoing hang-back recession, the success rate (+/- 10 prism diopters [PD]) was 80% in the conventional group and 74% in the hang-back group at 6 weeks. The dose-response curves were nearly identical. These results confirm that hang-back recessions for infantile and acquired esotropia are a predictable alternative to conventional strabismus surgery.

Child↗
PubMed1988

The Wilmer Information System. A classification and retrieval system for information on diagnosis and therapy in ophthalmology.

The Wilmer Information System is a computerized medical information system used for the storage and retrieval of data pertaining to patient demographics, diagnosis, and therapy. The heart of the system is an expandable, hierarchical code based on International Classification of Diseases, 9th Revision (ICD-9) diagnosis codes and Physicians' Current Procedural Terminology procedure codes. Customized coding sheets containing highly specific diagnosis and procedure codes have been designed for each subspecialty area in ophthalmology. Interactive database management software facilitates data entry and retrieval. The system can be used to search for patients who meet very specific criteria, or to produce cumulative visit reports and summary statistics.

Computers↗
PubMed1987

Centering corneal surgical procedures.

Currently used methods for centering corneal surgical procedures emphasize the visual axis of the eye but do not define it properly. We obtained the best optical result by centering the surgical procedure on the line of sight and entrance pupil of the eye, not on the visual axis. We found an error of 0.5 to 0.8 mm in currently used methods of marking the visual axis, which arose from the use of the corneal light reflex as a sighting point or from inadvertent monocular sighting in techniques requiring binocular sighting. Proper centering requires the patient to fixate on a point that is coaxial with the surgeon's sighting eye, and the cornea is marked at the point in line with the center of the patient's entrance pupil, ignoring the corneal light reflex.

Cornea↗
PubMed1987

Intraocular lens style and refraction in eyes treated with silicone oil.

The comparatively high refractive index of silicone oil significantly alters the refractive power of the human eye when it is placed into the vitreous cavity during retinal reattachment surgery. If cataract extraction and intraocular lens (IOL) implantation are subsequently performed, significant refractive errors result with most IOL styles if standard formulas are used to determine lens power. Thick-lens optical analysis of four IOL styles showed that the meniscus style yields the smallest difference between predicted (Binkhorst, Sanders-Retzlaff-Kraff formulas) and actual postoperative refraction. This IOL style also minimizes the change in refractive error that accompanies subsequent alterations in the contents of the vitreous cavity, including removal of silicone oil and replacement with balanced salt solution.

Eye↗