Ptosis is an abnormal drooping of the upper eyelid. Normally, upper lid covers about upper one sixth of the cornea, i.e., 2mm. Therefore, in this case. it covers more than 2mm.
Types of Ptosis
A. Congenital ptosis
It is associated with congenital weakness(maldevelopment) of the levator palpebrae superioris(LPS) muscle.
Characteristic features of congenital ptosis
- Drooping of one or both upper lids more often since birth of variable severity (mild, moderate, or severe).
- Lid crease is either diminished or absent.
- Lad lag on downgaze (i.e., ptotic lid is higher than the normal) due to tethering effect of abnormal LPS muscle. This is in contrast to acquired ptosis in which ptotic lid is lower than the normal in downgaze also.
- LPS function may be poor, fair or good depending upon the degree of weakness
B. Acquired Ptosis
Depending upon the cause it can be neurogenic. myogenic, aponeurotic or mechanical.
1. Neurogenic ptosis
It is caused by innervational defects such as:
- Third nerve palsy
- Horner’s syndrome,
- Ophthalmoplegic migraine, and
- Multiple sclerosis.
Horner’s syndrome, occuring due to oculo-sympathetic paresis, is characterized by classic triad of:
- Mild ptosis (due to paralysis of Muller’s muscles),
- Miosis (due to paralysis of dilator pupillae), and
- Reduced ipsilateral sweating (anhydrosis),
- Other features include mild enophthalmos, loss of cilio-spinal reflex, heterochromia, i.e., ipsilateral iris is lighter in color, pupil is slow to dilate, and there occurs slight elevation of the lower eyelid.
2. Acquired myogenic ptosis
It occurs due to acquired disorders of the LPS muscle or of the myoneural junction. It may be seen in patients with myasthenia gravis, dystrophia myotonica, ocular myopathy, oculopharyngeal muscular dystrophy and following trauma to the LPS, muscle thyrotoxicosis, and Lambert-Eaton myasthenia syndrome.
3. Aponeurotic ptosis
It develops due to defects of the levator aponeurosis in the presence of a normal functioning muscle. It includes:
- Involutional (senile) ptosis,
- Postoperative ptosis (which is rarely observed after cataract and retinal detachment surgery),
- Due to aponeurotic weakness associated with blepharochalasis, and
- Traumatic dehiscence or disinsertion of the aponeurosis.
4. Mechanical ptosis
It may result due to excessive weight on the upper lid as seen in patients with lid tumours, multiple chalazia and lid oedema. It may also occur due to scarring (cicatricial) as seen in patients with ocular pemphigoid and trachoma.
Following scheme may be adopted for work up of a patient:
It should include age of onset, family history, history of trauma, eye surgery and variability in degree of the ptosis.
1. Exclude pseudoptosis (simulated ptosis) on inspection. Its common causes are:
- Ipsilateral conditions such a microphthalmos, phthisis bulbi, enophthalmos, prosthesis, brow ptosis, dermatochalasis, and hypotropia.
- Contralateral conditions include: eyelid retraction, high myopia, and proptosis.
2. Observe the following points in each case:
- Whether ptosis is unilateral or bilateral. Causes of bilateral ptosis include congenital ptosis, myasthenia gravis, myotonic dystrophy, Kearns Sayre syndrome, Lambert-Eaton myasthenic syndrome, and chronic progressive external ophthalmoplegia.
- Function of orbicularis oculi muscle.
- Eyelid crease is present or absent.
- Jaw-winking phenomenon is present or not.
- Associated weakness of any extraocular muscle.
- Bell’s phenomenon (up and outrolling of the eyeball during forceful closure) is present or absent.
3. Measurement of amount (degree) of ptosis
- In unilateral cases, difference between the vertical height of the palpebral fissures of the two sides indicates the degree of ptosis.
- In bilateral cases it can be determined by measuring the amount of cornea covered by the upper lid and then subtracting 2 mm. Ptosis is graded depending upon its amount as:
- Mild ptosis: 2mm
- Moderate ptosis: 3mm
- Severe ptosis: 4mm
4. Marginal reflex distance (MRD)
It refers to the distance between the upper lid margins and corneal light reflex (of a pen torch held in front, on which patient is looking). Normal value of MRD is 4-5 mm.
5. Assessment of levator function
It is determined by the lid excursion caused by LPS muscle (Burke’s method). Patient is asked to look down, and thumb of one hand is placed firmly against the eyebrow of the patient (to block the action of frontalis muscle) by the examiner. Then the patient is asked to look up and the amount of upper lid excursion is measured with a ruler held in the other hand by the examiner. Levator function is graded as follows:
- Normal: 15mm
- Good: 8mm or more
- Fair: 5-7mm
- Poor: 4mm or less
6. Special investigations
Those required in patients with acquired ptosis are as follows:
- Tensilon test is performed when myasthenia is suspected. There occurs improvement of ptosis with intravenous injection of edrophonium (Tensilon) in myasthenia.
- Phenylephrine test is carried out in patients suspected of Horner’s syndrome.
- Neurological investigations may be required to find out the cause in patient with neurogenic ptosis.
7. Photographic record
Photographic record of the patient should be maintained for comparision. Photographs should be taken in primary position as well as in up and down gazes.
It almost always needs surgical correction. In severe posis, surgery should be performed at the earliest to prevent stimulus deprivation amblyopia. However, amild and moderate one, surgery should be delayed until the age of 34 years, when accurate measurements are possible. Congenital ptosis can treated by any of the following operations:
1. Tarso-conjunctivo-Mullerectomy (Fasanella-servat operation)
It is performed in cases having mild one (1.5- 2mm) and good levator function. In it, upper lid is everted and the upper tarsal botder along with its attached Muller’s muscle and conjunctiva are resected.
2. Levator resection
It is a very commonly performed operation for moderate and severe grades. It is contraindicated in patients having severe ptosis with poor levator function.
Amount of levator resection required
Generally, Most of the surgeons find it out by adjusting the lid margin in relation to cornea during operation on the table in individual case. However, a rough estimate in different grades of ptosis can be made:
Moderate: Depending on the level of LPS function the amount of LPS to be resected is as below:
- Good function: 16-17 mm (minimal)
- Fair function: 18-22 mm (moderate)
- Poor function: 23-24 mm (maximum)
Severe: Fair levator function: 23-24 mm (maximum LPS resection)
Levator muscle may be resected by either conjunctival or skin approach.
i. Conjunctival approach (Blaskowics’ operation)
This technique is comparatively easy but not suitable for large amount of resection. In it LPS muscle is exposed by an incision made through the conjunctiva near the upper tarsal border, after the upper lid is doubly everted over a Desmarre’s lid retractor.
ii. Skin approach (Everbusch’s operation):
It is a more frequently employed technique. Thus, it allows comparatively better exposure of the LPS muscle through a skin incision along the line of future lid crease.
3. Frontalis sling operation (Brow suspension)
This is performed in patients having severe one with no levator function. In this operation, lid is anchored to the frontalis muscle via a sling. Fascia lata (best material) or some non-absorbable material (e.g., supramide suture, silicon rod) may he be used as sling.
Treatment of acquired ptosis
- Treat the underlying cause wherever possible.
- Conservative treatment should be carried out and surgery deferred at least for 6 months in neurogenic ptosis.
- Surgical procedures (when required) for acquired ptosis are essentially the same as described for congenital ptosis. However, the amount of levator resection required is always less than the congenital one of the same degree. Further, in most cases the simple Fasanella-Servat procedure is adequate.
For more information follow the link (https://en.wikipedia.org/wiki/Ptosis_(eyelid))