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Biomedical subjects

S Shippman

Publications and source records attributed to S Shippman.

10 recordsLinked to original sources
PubMed1999

Aniseikonia quantification: error rate of rule of thumb estimation.

PURPOSE: To find the error rate in quantifying aniseikonia by using "Rule of Thumb" estimation in comparison with proven space eikonometry. METHODS: Study 1: 24 adult pseudophakic individuals were measured for anisometropia, and astigmatic interocular difference. Rule of Thumb quantification for prescription was calculated and compared with aniseikonia measurement by the classical Essilor Projection Space Eikonometer. Study 2: parallel analysis was performed on 62 consecutive phakic patients from our strabismus clinic group. RESULTS: Frequency of error: For Group 1 (24 cases): 5 ( or 21 %) were equal (i.e., 1% or less difference); 16 (or 67% ) were greater (more than 1% different); and 3 (13%) were less by Rule of Thumb calculation in comparison to aniseikonia determined on the Essilor eikonometer. For Group 2 (62 cases): 45 (or 73%) were equal (1% or less); 10 (or 16%) were greater; and 7 (or 11%) were lower in the Rule of Thumb calculations in comparison to Essilor eikonometry. Magnitude of error: In Group 1, in 10/24 (29%) aniseikonia by Rule of Thumb estimation was 100% or more greater than by space eikonometry, and in 6 of those ten by 200% or more. In Group 2, in 4/62 (6%) aniseikonia by Rule of Thumb estimation was 200% or more greater than by space eikonometry. CONCLUSION: The frequency and magnitude of apparent clinical errors of Rule of Thumb estimation is disturbingly large. This problem is greatly magnified by the time and effort and cost of prescribing and executing an aniseikonic correction for a patient. The higher the refractive error, the greater the anisometropia, and the worse the errors in Rule of Thumb estimation of aniseikonia. Accurate eikonometric methods and devices should be employed in all cases where such measurements can be made. Rule of thumb estimations should be limited to cases where such subjective testing and measurement cannot be performed, as in infants after unilateral cataract surgery.

Adult↗
PubMed1999

A study of aniseikonia and Knapp's law using a projection space eikonometer.

PURPOSE: Knapp's Law, which states that anisometropias due to varying abnormal axial lengths between eyes would not result in inequality in relative retinal image size, provided the correcting spectacle lens was placed at the far point of the eye, has been shown to fall short in clinical practice in several studies using "direct comparison eikonometry". To test these findings using space eikonometry and to further elucidate this Law's clinical applicability, the following study was conducted. METHODS: Thirteen patients with suspected axial anisometropia of at least 4 Diopters were identified, selected and examined. Cycloplegic refraction, A-scan ultrasonic ocular biometry and Essilor Projection Space Eikonometry were performed. RESULTS: Ten of the thirteen patients had their anisometropia due primarily to ocular axial length differences. Of these ten, seven (70%) had detectable levels of aniseikonia and 3 (30%) demonstrated no aniseikonia. The other three patients whose aniso-metropia was due to combined axial and refractive components, all had aniseikonia. CONCLUSION: As a geometric optics theory, Knapp's Law stands on its own merits. However, in clinical practice, reduction in retinal element density in high myopia limits its applicability. Such patients often do have significant aniseikonia which can produce ocular referable complaints and/or interfere with binocular vision.

Adolescent↗
PubMed1999

Aniseikonia in relation to strabismus, anisometropia and amblyopia.

PURPOSE: To study the interrelationships among these four entities which are critical to binocular vision and its precision. SUBJECTS AND METHODS: 102 selected patients (for their ability to have stereoscopic depth perception, a requisite for space eikonometry) were evaluated. Patient testing included stereoscopic testing, Essilor Projection Space Eikonometry, ultrasonic echographic axial length measurements and orthoptic evaluation. Aniseikonia was measured on the Essilor Projection Space Eikonometer. RESULTS: 1. Anisometropia alone was correlated with a marked increase in amblyopia, a moderate increase in aniseikonia and no noteworthy increase in strabismus. Statistical analysis (chi square ratio) showed that persons with elevated anisometropic values had a 4.4 fold increased risk of aniseikonia (p=.003). 2. Aniseikonia alone was not responsible for marked variations in strabismus. 3. Amblyopia was correlated with increases in anisometropia and aniseikonia. 4. Adding aniseikonia to anisometropia produced a possible increase in strabismus and a great increase in amblyopia (using Fisher's Exact Test, 2-tailed). 5. Spearman correlations of the "absolute values" (the mean of the mathematical difference between the two eyes of anisometropia and amblyopia) were as follows: anisometropia (abs) vs. aniseikonia r=.294, p=.006; anisometropia (abs) vs. amblyopia (abs) 4=.555, p=<.001; amblyopia (abs) vs. aniseikonia r=.234, p=.02. CONCLUSIONS: Aniseikonia per se does not appear to have a major causal role in amblyopia or strabismus, but anisometropia does for amblyopia. This role is greatly augmented by aniseikonia and this combination may then produce strabismus.

Amblyopia↗
PubMed1983

Relationship of heterophoria to stereopsis.

Eighty patients with 6/7.5 (20/25) or better visual acuity in each eye noted differences in stereoacuity with crossed and uncrossed disparity. Esophoric patients who perceived a difference were more likely to have greater stereoacuity with uncrossed disparity, and exophoric patients who perceived a difference were more likely to have greater stereoacuity with crossed disparity. Asymmetry of Panum's area may be a factor in this phenomenon.

Esotropia↗
PubMed1983

Paradoxical inferior oblique muscle overaction with A-pattern esotropia.

The presence of overacting inferior oblique muscles in A-pattern esotropia is a rarely documented finding. During the last three decades, three basic schools of thought have evolved to explain A and V patterns. In certain cases an individualized approach synthesizing these three theories is needed. We saw two patients with paradoxical A-pattern esotropia with inferior oblique muscle overaction. Both cases were treated surgically by weakening both inferior oblique muscles with recession and supraplacement of both medial rectus muscles. The synthesis of these two approaches resulted in good postoperative alignment.

Child, Preschool↗
PubMedDate not supplied

Antipodean squint.

Strabismic cases which are exotropic fixing with one eye, and esotropic fixing with the other eye are rare and a result of anisometropia, unequal accommodation, paresis or restriction, and previous ocular muscle surgery. Three cases of antipodean squint are reported without known etiology factor. An extensive survey of experts in the field of strabismus was unable to document other similar cases where a cause could not be determined.

Accommodation, Ocular↗
PubMedDate not supplied

Accommodative esotropia in adults.

The accommodative convergence/accommodation (AC/A) ratio is thought to be fixed throughout life. We present 11 patients who, in adulthood, show a situational increase in their AC/A ratio. Since all patients had a history of accommodative esotropia with and without a nonaccommodative component, we feel the situational increase in the AC/A ratio is in response to the additional effort needed to correct the patients' facultative hyperopia. These patients demonstrate the importance that all adults with acute onset of commitant esotropia and a history of accommodative esotropia should wear full correction before a prism is incorporated into their glasses or surgical intervention is considered.

Accommodation, Ocular↗