Anatomy & Physiology
Occupational & Environmental Medicine
Several reproducible themes have been noted in the analysis of beautiful eyes. The palpebral fissure should be almond shaped and symmetrical between the two sides, with the highest point of the upper eyelid at the medial limbus and the lowest point of the lower eyelid at the lateral limbus. Canthal angles should be sharp, especially at the lateral canthus, which should lie 2 to 4 mm superior to the medial canthus. The horizontal dimension of the palpebral fissure is 25 to 30 mm, whereas its vertical dimension is approximately 10 mm. Vertical palpebral asymmetry may indicate the presence of true ptosis of the eyelid, which would necessitate ptosis repair. The upper eyelid orbicularis muscle should be smooth and flat, and the upper eyelid crease should be crisp. The upper lid crease should lie between 8 and 12 mm from the lid margin in a white patient. A more inferior position of the upper lid crease gives a heavy and tired appearance to the eye. Excessive lid folds—that is, tissue that prolapses over the upper eyelid crease—should be minimal to avoid an aged and tired look. The upper lid margin should cover 1 to 2 mm of the superior limbus, whereas the lower lid margin should lie at the inferior limbus or 1 mm below it. Note should be made of excessive skin, muscle, and orbital fat; the pinch test helps determine the degree of excess lid skin that is present. The snap test helps determine the degree of lower lid laxity and is useful in preoperative planning; the lower eyelid is distracted from the globe, and an audible snap should be heard if the eyelid is not significantly lax. Additionally, a ptotic lacrimal gland must be recognized for potential correction at surgery. Excessive lateral skin hooding may require skin excision beyond the lateral orbital rim, and prolonged wound healing would be expected in this area of greater skin thickness—a point that must be relayed to the patient before surgical intervention.
The lower eyelid should closely appose the globe without the lid drooping away from the globe (ectropion) or in toward the globe (entropion). Excessive lower eyelid laxity should be recognized with the snap test, and when present, a lid-shortening/lid-tightening procedure should be performed in conjunction with blepharoplasty. Exophthalmos and enophthalmos should be recognized: neither is favorable, and each may represent an underlying disorder. Visual acuity should be evaluated, as should the presence of a Bell phenomenon. Absence of the Bell phenomenon places the patient at increased risk for development of postoperative corneal abrasions if temporary or permanent lagophthalmos occurs after surgery. If the patient exhibits signs of a dry eye, the Schirmer test should be performed, and caution should be used in deciding on surgical intervention.
Upper Eyelid Ptosis
The ptotic eyelid is often masked by dermatochalasis, so preoperative attention should be given to identifying and classifying upper eyelid ptosis. Blepharoplasty alone of the ptotic lid may lead to an unfavorable cosmetic result and a need for additional surgery. The most common cause for eyelid ptosis is secondary to acquired involutional changes, although the patient should also be assessed for myogenic, neurogenic, and mechanical causes as well as for pseudoptosis.
The degree of ptosis can be quantified by the margin-reflex distance (MRD). This is the distance between the central corneal light reflex and the upper lid margin, usually around 3 to 4.5 mm. Asymmetry between lids is not uncommon and is usually reflected in the MRD. Normally, the upper lid margin should rest about 1 mm below the tangent of the superior limbus. The light should be held between the examiner’s eyes (coaxial to the examiner’s observation axis), and the examiner’s eyes should be level with those of the patient. The light should not be too bright, or the patient may squint and the result will be an artificially low measurement. The highest point in the upper lid is just medial to midline near the medial limbus, and it has a greater curvature than the lower lid margin, whose lowest point is near or at the midline. In addition to the MRD, the central interpalpebral distance, which is another measure of comparison between lids, should also be recorded. Normally 8 to 10 mm, the central interpalpebral distance is the distance from the upper lid margin and the lower lid margin at their highest points. A patient with ptosis of the upper lid and retraction of the lower lid may also have “normal” palpebral fissure measure.
The levator function is helpful in distinguishing the potential etiologies of the ptosis as well as in planning surgery. It is assessed by measuring the excursion of the upper lid margin in extreme downgaze to extreme upgaze. The brow should be fixated by the examiner to prevent recruitment of the frontalis.
Normal function is usually greater than 12 mm. Levator shortening procedures potentially have a good pro
Source: Cummings Otolaryngology, 6E (2015)
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